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You've reached the internet home of Chris Sells, Program Manager in the Distributed Systems Group at Microsoft. This site is targeted at the Windows developer. Enjoy.



Thursday, Aug 26, 2010, 7:12 AM

The Downside Of Working At Home

I've been working at home off and (mostly) on for 16 years...

From theoatmeal.com. Recommended!

21 comments



Sunday, Aug 8, 2010, 8:19 AM

Why can't it all just be messages?

My mobile device is driving me crazy.

I have an iPhone 4.0. Normally when it's driving me crazy, it's standard stuff like the battery life sucks or that the iOS 4.0.1 update didn't fix the proximity detection or stop emails I send via Exchange from just disappearing into the ether.

This time, it's something else and I can't blame the iPhone; I think all modern smart phones have the same problem. The problem is that I constantly have to switch between apps to see my messages. Here are screenshots for 5 of the messaging clients I use reguarly:

Voicemail Exchange Email SMS/MMS Facebook Twitter

This list doesn't include real-time messages like IM, or notifications like Twitter or RSS. I'm just talking about plain ol' async messaging. We used to think of it as "email," but really voicemail, email, SMS, MMS, Facebook messages and Twitter Direct Messages are all the same -- they are meant to queue up until you get to them.

Now, some folks would argue that SMS/MMS aren't meant to be queued; they're meant to be seen and handled immediately. Personally, I find it annoying that there is a pop-up for every single text or media messages I get on my phone and there seems to be no way to turn that off. On the other hand, if I want that to happen for other types of messages, e.g. voicemail, I can find no way to turn it on even if I want to. Why are text messages special, especially since most mobile clients let you get over the 160 character limit and will just send them one after the other for you anyway?

iOS 4 takes a step in the right direction with the "universal" inbox:

iOS4 "universal" inbox

Here I've got a great UI for getting to all my email messages at once, but why can't it handle all my messages instead?

super-universal inbox

Not only would this put all my messages in one place at one time, but it would unify up the UI and preferences across the various messaging sources. Do you want your text messages to quietly queue up like email? Done. Do you want your voicemail to pop to the front like an SMS? Done. Do you want the same swipe-to-delete gestures on your voicemail as you have with your email? Done!

Maybe someone with some experience on the new Windows Phone 7 can tell me that there is a "messaging" hub that manages all this for me. Since they're already doing things like bringing facebook pictures into the "pictures" hub (or whatever they call it), that doesn't seem completely out of the realm of possibility. If that's the case, I'll say again what I've been saying for a while -- I can't wait for my Windows Phone 7!

15 comments



Friday, Jun 18, 2010, 11:43 AM

David Ramel Asks About Interviewing at Microsoft

David Ramel from 1105media.com is writing an article that includes the Microsoft interviewing process and he send me some questions:

[David] How would you succinctly sum up the Microsoft interview process as compared to those of other tech companies?

[Chris] MS does some things similarly to other high-tech companies I've worked with, e.g. having each interviewer focus on an aspect or aspects, e.g. team skills, people skills, technical skills, etc., expecting a candidate to ask questions, communicating between interviewers to push more on one area or another, etc. The riddle questions are a uniqueness at Microsoft (at least they were when I last interviewed), but theyire pretty rare these days. Coding on the whiteboard also seems pretty unique to Microsoft (myself, I prefer the keyboard : ).

[David] How has the Microsoft interview process changed over time? (Microsoft seems to have shaken up the tech interview process some years ago with those brain-teasing puzzle� questions, but now seem to be much more technically-oriented and job-specific. Just wondering about your thoughts on this observation.)

[Chris] While I have had them, puzzle questions were rare even when I was interviewed 7 years ago. Since then, I haven't run into many people that use them. However, when they are used, an interviewer is often looking for how a candidate works through an issue as much as the solution that they come up with. In an ever changing world, being able to learn and adapt quickly is a huge part of how successfully you can be in the tech industry at all and at Microsoft specifically. I prefer technical design questions for these kinds of results, however, and it seems that most 'softies agree.

[David] What would you say was the biggest factor in your being offered a job at Microsoft?

[Chris] I had a reputation outside of MS before I interviewed, but that almost didn't matter. If I hadn't done well during the interview, I would not have been offered the job. When in doubt, a team generally prefers to turn away a good candidate rather than to risk taking on a bad one, so if there's anything wrong, team fit, technical ability, role fit, etc., a candidate won't get an offer.

[David] What's the single most important piece of advice you can offer to those preparing for a Microsoft job interview?

[Chris] You asked for just one, but I'm going to give you two anyway. : )

  1. If you need more information to answer a question, ask for it. Thatis how the real-world works and many questions are intentionally vague to simulate just this kind of interaction.
  2. Try to answer non-technical questions based on your personal experience, e.g. instead of saying "here's how I would deal with that situation,"� say "I had a similar situation in my past and hereis how I dealt with it."� This is a style of interviewing known as behavioral� and even if your interviewer doesn't phrase his questions in that way, e.g. "give me an example of how you dealt with a situation like blah,"� it's helpful and impressive if you can use your own history to pull out a positive result.

[David] Could you please share any other observations you have on the Microsoft interview process that may not be covered in your site or the Jobsblog?

[Chris] I run a little section of my web site dedicated to the MS interviewing process and the thing I will tell you is this: don't prepare. Be yourself. If you're not a fit for MS, no amount of preparation in the days before an interview will help and if you are a fit, that will come through in the interview. Also, make sure you ask questions. Working at Microsoft isn't just a job, it's a way of life, so make sure you're sure you want the team and the job for which you're interviewing.

[David] Does MS provide training for interviewers? If so, what do they stress most?

[Chris] I'm sure MS does provide training for interviewing, but Iive never been to it. At Intel, I learned the behavioral interviewing technique, which Iive used in every interview since, both as an interviewer and as a job candidate.

[David] Do you have standard questions, or do you tailor them to the situation? If the latter, is it usually tailored for team fit, to a specific open position, particular skills, etc.?

[Chris] I have once standard technique question and a few standard behavioral interview questions. The technical question is to ask them what their favorite technology is and/or what they consider themselves to be an expert� in and then drill in on their understanding. If they can answer my questions deeply, this shows passion about technology and the ability to learn something well, both of which are crucial for success at MS.

My behavioral interviewing questions are things like "Tell me about a time when youive been in conflict with a peer. How did you resolve it? What was the result? What did you learn?"� and "Tell me about a time when you had much too much work to do in the time you were given. How do you resolve that issue? What was the result? What did you learn?"� The core idea of behavioral interviewing is that past behavior indicates future behavior, so instead of asking people things like "How would you deal with such-and-such?�" you ask them "How did you dealt with such-and-such in the past?"� This forces them to find a matching scenario and you get to see if they way they dealt with the issue in real life matches what you want from a team mate in that job.

[David] How would you describe the kinds of coding questions you ask? A couple of real examples would be perfect!

[Chris] I don't often ask coding questions, but when I have, I let them use a keyboard. I hate coding on the board myself as it's not representative of how people actually code, so I don't find it to be a good indicator of what people will actually do. I guess I even use behavioral techniques for technical questions, now that I think about it. : )

2 comments



Sunday, May 23, 2010, 8:40 PM

Spurious MachineToApplication Error With VS2010 Deployment

Often when I'm building my MVC 2 application using Visual Studio 2010, I get the following error:

It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS.

On the internet, this error seems to be related to having a nested web.config in your application. I do have such a thing, but it's just the one that came out of the MVC 2 project item template and I haven't touched it.

In my case, this error in my case doesn't seem to have anything to do with a nested web.config. This error only started to happen when I began using the web site deployment features in VS2010 which by itself, rocks (see Scott Hanselman's "Web Deployment Made Awesome: If You're Using XCopy, You're Doing It Wrong" for details).

 If it happens to you and it doesn't seem to make any sense, you can try to fix it with a Build Clean command. If you're using to previous versions of Visual Studio, you'll be surprised, like I was, not to find a Clean option in sparse the Build menu. Instead, you can only get to it by right-clicking on your project in the Solution Explorer and choosing Clean.

Doing that, however, seems to make the error go away. I don't think that's a problem with my app; I think that's a problem with VS2010.

6 comments



Thursday, May 20, 2010, 6:11 PM

a whole new sellsbrothers.com

The new sellsbrothers.com implementation has been a while in the making. In fact, I've had the final art in my hands since August of 2005. I've tried several times to sit down and rebuild my 15-year-old sellsbrothers.com completely from scratch using the latest tools. This time, I had a book contract ("Programming Data," Addison-Wesley, 2010) and I needed some real-world experience with Entity Framework 4.0 and OData, so I fired up Visual Studio 2010 a coupla months ago and went to town.

The Data Modeling

The first thing I did was design my data model. I started very small with just Post and Comment. That was enough to get most of my content in. And that lead to my first principle (we all need principles):

thou shalt have no .html files served from the file system.

On my old site, I had a mix of static and dynamic content which lead to all kinds of trouble. This time, the HTML at least was going to be all dynamic. So, once I had my model defined, I had to import all of my static data into my live system. For that, I needed a tool to parse the static HTML and pull out structured data. Luckily, Phil Haack came to my rescue here.

Before he was a Microsoft employee in charge of MVC, Phil was well-known author of the SubText open source CMS project. A few years ago, in one of my aborted attempts to get my site into a reasonable state (it has evolved from a single static text file into a mish-mash of static and dynamic content over 15 years), I asked Phil to help me get my site moved over to SubText. To help me out, he built the tool that parsed my static HTML, transforming the data into the SubText database format. For this, all I had to do was transform the data from his format into mine, but before I could do that, I had to hook my schema up to a real-live datastore. I didn't want to have to take old web site down at all; I wanted to have both sites up and running at the same time. This lead to principle #2:

thou shalt keep both web sites running with the existing live set of data.

And, in fact, that's what happened. For many weeks while I was building my new web site, I was dumping static data into the live database. However, since my old web site sorting things by date, there was only one place to even see this old data being put in (the /news/archive.aspx page). Otherwise, it was all imperceptible.

To make this happen, I had to map my new data model onto my existing data. I could do this in one of two ways:

  1. I could create the new schema on my ISP-hosted SQL Server 2008 database (securewebs.com rocks, btw -- highly recommended!) and move the data over.
  2. I could use my existing schema and just map it on the client-side using the wonder and beauty that was EF4.

Since I was trying to get real-world experience with our data stack, I tried to use the tools and processes that a real-world developer has and they often don't get to change the database without a real need, especially on a running system. So, I went with option #2.

And I'm so glad I did. It worked really, really well to change names and select fields I cared about or didn't care about all from the client-side without ever touching the database. Sometimes I had to make database changes and when that happened, I has careful and deliberate, making the case to my inner DB administrator, but mostly I just didn't have to.

And when I needed whole new tables of data, that lead to another principle:

build out all new tables in my development environment first.

This way, I could make sure they worked in my new environment and could refactor to my heart's content before disturbing my (inner) DB admin with request after request to change a live, running database. I used a very simple repository pattern in my MVC2 web site to hide the fact that I was actually accessing two databases, so when I switched everything to a single database, none of my view or controller code had to change. Beautiful!

Data Wants To Be Clean

And even though I was careful to keep my schema the same on the backend and map it as I wanted in my new web site via EF, not all of my old data worked in my new world. For example, I was building a web site on my local box, so anything with a hard-coded link to sellsbrothers.com had to be changed. Also, I was using a set of <a name="tag" ? elements to reference specific posts in my static HTML that just didn't scale to my dynamic ID-based permalinks, so data had to be "cleaned."

To do this cleaning, I used a combination of LINQPad, SSMS and EF-based C# code to perform data cleaning tasks. This yielded two tools that I'm still using:

  1. BlogEdit: An unimagintively named general-purpose post and comment creation and editing tool. I built the first version of this long before WPF, so kept hacking on it in WinForms (whose data binding sucks compared to WPF, btw) as I needed it to have new features. Eventually I gave this tool WYSIWIG HTML editing by shelling out to Expression Web, but I need real AtomPub support on the site so I can move to Windows Live Writer for that functionality in the future.
  2. BulkChangeDatabaseTable: This was an app that I'd use to run my questions to find "dirty" data, perform regular expression replaces with and then -- and this is the best part -- show the changes in WinDiff so I could make sure I was happy with the changes before commiting them to the database. This extra eyeballing saved me from wrecking a bunch of data.

During this data cleaning, I applied one simple rule that I adopted early and always regretted when I ignored:

thou shalt throw away no data.

Even if the data didn't seem to have any use in the new world, I kept it. And it's a good thing I did, because I always, always needed it.

For example, when I ran Phil's tool to parse my static web pages, he pulled out the <a name="tag" /> tags that went with all of my static posts. I wasn't going to use them to build permalinks, why did I need them?

I'll tell you why: because I've got 2600 posts in my blog from 15 years of doing this, I cross-link to my own content all the live-long day and a bunch of those cross-links are to, you guessed it, to what used to be static data. So, I have to turn links embedded in my content of the form "/writing/#footag" into links of the form "/posts/details/452". But how do I look up the mapping between "footag" and "452"? That's right -- I actually went to my (inner) DB admin and begged him for a new column on my live database called "EntryName" where I tucked the <a name="tag" /> data as I imported the data from Phil's tool, even though I didn't know why I might need it. It was a good principle.

Forwarding Old Links

And how did I even figure out I had all those broken links? Well, I asked my good friend and web expert Kent Sharkey how to make sure my site was at least internally consist before I shipped it and he recommended Xenu Link Sleuth for the job. This lead to another principle:

thou shalt ship the new site with no broken internal links.

Which was followed closely by another principle:

thou shalt not stress over broken links to external content.

Just because I'm completely anal about making sure every link I ever pass out to the world stays valid for all eternity doesn't mean that the rest of the world is similiarly anal. That's a shame, but there's nothing I can do if little sites like microsoft.com decide to move things without a forwarding address. I can, however, make sure that all of my links worked internally and I used Xenu to do that. I started out with several hundred broken links and before I shipped the new site, I had zero.

Not all of that was changing old content, however. In fact, most of it wasn't. Because I wanted existing external links out in the world to find the same content in the new place, I had to make sure the old links still worked. That's not to say I was a slave to the old URL format, however. I didn't want to expose .aspx extensions. I wanted to do things the new, cool, MVC way, i.e. instead of /news/showTopic.aspx?ixTopic=452 (my old format), I wanted /posts/details/452. So, this lead to a new principle:

thou shalt built the new web site the way you want and make the old URLs work externally.

I was using MVC and I wanted to do it right. That meant laying out the "URL space" the way it made sense in the new world (and it's much nicer in general, imo). However, instead of changing my content to use this new URL schema, I used it as a representative sample of how links to my content in the real-world might be coming into my site, which gave me initial data about what URLs I needed to forward. Ongoing, I'll dig through 404 logs to find the rest and make those URLs work appropriately.

I used a few means of forwarding the old URLs:

  1. Mapping sub-folders to categories: In the old site, I physically had the files in folders that matched the sub-folders, e.g. /fun mapped to /fun/default.aspx. In the new world, /fun meant /posts/details/?category=fun. This sub-folder thing only works for the set of well-defined categories on the site (all of which are entries in the database, of course), but if you want to do sub-string search across categories on my site you can, e.g. /posts/details/?category=foo.
  2. Kept sub-folder URLs, e.g. /tinysells and /writing: I still liked these URLs, so I kept them and built controllers to handle them.
  3. Using the IIS URL Rewriter: This was the big gun. Jon Galloway, who was invaluable in this work, turned me onto it and I'm glad he did. The URL Rewriter is a small, simple add-in to IIS7 that lets you describe patterns and rules for forwarding when those patterns are matched. I have something like a dozen patterns that do the work to forward 100s of URLs that are in my own content and might be out in the world. And it works so, so well. Highly recommended.

So, with a combination of data cleaning to make my content work across both the old site and the new site under development, making some of my old URLs work because of conventions I adopted that I wanted to keep and URL rewriting, I had a simple, feature-complete, 100% data-driven re-implementation of sellsbrothers.com.

What's New?

Of course, I couldn't just reimplement the site without doing something new:

The Room for Improvement

As always, there's a long list of things I wish I had time to do:

Luckily, with the infrastructure I've got in place now, laying in these features over time will be easy, which was the whole point of doing this work in the first place.

Where are we?

All of this brings me back to one more principle. I call it Principle Zero:

thou shalt make everything data-driven.

I'm living the data-driven application dream here, people. When designing my data model and writing my code, I imagined that sellsbrothers.com was but one instance of a class of web applications and I kept all of the content, down to my name and email address, in the database. If I found myself putting data into the code, I figured out where it belonged in the database instead.

This lead to all kinds of real-world uses of the database features of Visual Studio, including EF, OData, Database projects, SQL execution, live table-based data editing, etc. I lived the data-driven dream and it yielded a web site that's much faster and runs on much less code:

Do the math and that's 100+% of the content and functionality for 10% of the code. I knew I wanted to do it to gain experience with our end-to-end data stack story. I had no idea I would love it so much.

9 comments



Tuesday, May 11, 2010, 3:53 PM

Entity Framework 4.0 POCO Classes and Data Services

If you've flipped on the POCO (Plain Ol' CLR Objects) code generation T4 templates for Entity Framework to enable testing or just 'cuz you like the code better, you might find that you lack the ability to expose that same model via Data Services as OData (Open Data). If you surf to the feed, you'll likely see something like this:

The XML page cannot be displayed

Cannot view XML input using XSL style sheet. Please correct the error and then click the Refresh button, or try again later.

The following tags were not closed: feed. Error processing resource 'http://localhost:10749/MyODataEndpoint.svc/Posts'

 

There are two problems. The first problem is that we're not reporting the problem very well. You can't see what's happening in IE8 with a simple View Source, as apparently IE won't show malformed XML. Instead, you have to use Fiddler or some other tool (I'm a big tcpTrace fan) to see the actual error in the HTTP response:

 

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<feed ...>
<title type="text">Posts</title>
<id>http://localhost:8080/MyODataEndpoint.svc/Posts</id>
<updated>2010-05-11T22:48:13Z</updated>
<link rel="self" title="Posts" href="Posts" />
<m:error>
<m:code></m:code>
<m:message xml:lang="en-US">Internal Server Error. The type
'System.Data.Entity.DynamicProxies.Post_CF2ABE5AD0B93AE51D470C9FDFD72E780956A6FD7294E0B4205C6324E1053422'
is not a complex type or an entity type.</m:message>
</m:error>

 

It's in the creation of the OData feed that the error happens, so instead of clearing the response and just returning the error, we dump it into the middle of the output, making it very difficult to find. In this case, what we're telling you is that you've mistakenly left dynamic proxy creation on, which doesn't work with EF4 POCO objects and Data Services in .NET 4.0. To fix this, you need to override the CreateDataSource method in your DataService<T> derived class:

 
public class MyODataEndpoint : DataService<FooEntities> {
  public static void InitializeService(DataServiceConfiguration config) {
    ...
  }

  protected override sellsbrothersEntities CreateDataSource() {
    var dataSource = new FooEntities();
    dataSource.ContextOptions.ProxyCreationEnabled = false;
    return dataSource;
  }
}

 

This solution came from Shyam Pather, a Dev Manager on the EF team. He says that once you turn off proxy generation, you give up lazy loading and "immediate" change tracking. Instead, you'll get "snapshot" change tracking, which means the context won't be informed when the properites are changed, but the context still detects changes when you call DetectChanges() or SaveChanges(). For the internals of a Data Service, none of this matters, but any code you write in query interceptors, change interceptors, or service operations will have to be aware of this.

This limitations are only true when used from the OData endpoint, of course. The rest of your app will get proxy creation by default unless you turn it off.

0 comments



Friday, May 7, 2010, 3:40 PM

Working Hard: WhirlyBall

What my team does on an average Wednesday afternoon:

It was surprisingly fun.

2 comments



Thursday, May 6, 2010, 11:41 AM

We're taking OData on the Road!

We have a series of free, day-long events we're doing around the world to show off the beauty and wonder that is the Open Data Protocol. In the morning we'll be showing you OData and in the afternoon we'll help you get your OData services up and running. Come one, come all!

Your speakers are going to include Doug Purdy, so book now. Spots are going to go fast!

2 comments



Tuesday, Apr 20, 2010, 4:27 PM

SQL Server Modeling CTP (November 2009 Release 3) for Visual Studio 2010 RTM Now Available

Here's what Kraig has to say about the November 2010 SQL Server Model CTP that matches the RTM of Visual Studio 2010:

A update of the SQL Server Modeling CTP (November 2009) that's compatible with the official (RTM) release of Visual Studio 2010 is now available on the Microsoft Download Center.  This release is strictly an updated version of the original November 2009 CTP release to support the final release of Visual Studio 2010 and .NET Framework 4.

We highly recommend you uninstall and install in the following order.

  1. Uninstall any existing SQL Server Modeling CTP from Add and Remove Programs
  2. Uninstall Visual Studio 2010 and .NET Framework 4 Beta 2 or RC from Add and Remove Programs
  3. Install Visual Studio 2010 and .NET Framework 4
  4. Install the SQL Server Modeling November 2009 CTP Release 3.

If you are unable to uninstall SQL Server Modeling CTP from Add and Remove Programs for any reason, you can remove each component using the following command lines.  You need to run all three in order to completely remove SQL Server Modeling CTP so you can install the new CTP:

M Tools: Msiexec /x {B7EE8AF2-3DCC-4AFE-8BD2-5A6CE9E85B3A}

Quadrant: Msiexec /x {61F3728B-1A7D-4dd8-88A5-001CBB9D2CFA}

Domains: Msiexec /x {11DA75C8-10AB-4288-A1BB-B3C2593524A7}

Note: These steps will not remove the SQL Server Modeling CTP entry in Add and Remove Programs but you will be able to install the new CTP.

Thank you and enjoy Visual Studio 2010!

Kraig Brockschmidt
Program Manager, Data Developer Center

0 comments



Monday, Apr 5, 2010, 10:33 PM

The performance implications of IEnumerable vs. IQueryable

It all started innocently enough. I was implementing a "Older Posts/Newer Posts" feature for my new web site and was writing code like this:

IEnumerable<Post> FilterByCategory(IEnumerable<Post> posts, string category) {
  if( !string.IsNullOrEmpty(category) ) {
    return posts.Where(p => p.Category.Contains(category));
  }
}
...
  var posts = FilterByCategory(db.Posts, category);
  int count = posts.Count();
...

The "db" was an EF object context object, but it could just as easily been a LINQ to SQL context. Once I ran this code, it failed at run-time with a null reference exception on Category. "That's strange," I thought. "Some of my categories are null, but I expect the 'like' operation in SQL to which Contains maps to skip the null values." That should've been my first clue.

Clue #2 was when I added the null check into my Where expression and found that their were far fewer results than I expected. Some experimentation revealed that the case of the category string mattered. "Hm. That's really strange," I thought. "By default, the 'like' operation doesn't care about case." Second clue unnoticed.

My 3rd and final clue was that even though my site was only showing a fraction of the values I knew where in the database, it had slowed to a crawl. By now, those of you experienced with LINQ to Entities/SQL are hollering from the audience: "Don't go into the woods alone! IEnumerable kills all the benefits of IQueryable!"

See, what I'd done was unwittingly switched from LINQ to Entities, which takes my C# expressions and translates them into SQL, and was now running LINQ to Objects, which executes my expressions directly.

"But that can't be," I thought, getting hot under the collar (I was wearing a dress shirt that day -- the girlfriend likes me to look dapper!). "To move from LINQ to Entities/SQL to LINQ to Objects, I thought I had to be explicit and use a method like ToList() or ToArray()." Au contraire mon fraire (the girlfriend also really likes France).

Here's what I expected to be happening. If I have an expression like "db.Posts" and I execute that expression by doing a foreach, I expect the SQL produced by LINQ to Entities/SQL to look like this:

select * from Posts

If I add a Where clause, I expect the SQL to be modified:

select * from Posts where Category like '%whatever%'

Further, if I do a Count on the whole thing, e.g.

db.Posts.Where(p => p.Contains(category)).Count()

I expect that to turn into the following SQL:

select count(*) from Posts where Category like '%whatever%'

And that's all true if I keep things to just "var" but I wasn't -- I was being clever and building functions to build up my queries. And because I couldn't use "var" as a function parameter, I had to pick a type. I picked the wrong one: IEnumerable.

The problem with IEnumerable is that it doesn't have enough information to support the building up of queries. Let's take a look at the extension method of Count over an IEnumerable:

public static int Count<TSource>(this IEnumerable<TSource> source) {
  ...
  int num = 0;
  using (IEnumerator<TSource> enumerator = source.GetEnumerator()) {
    while (enumerator.MoveNext()) { num++; }
  }
  return num;
}

See? It's not composing the source IEnumerable over which it's operating -- it's executing the enumerator and counting the results. Further, since our example IEnumerator was a Where statement, which was in turn a accessing the list of Posts from the database, the effect was filtering in the Where over objects constituted from the following SQL:

select * from Posts

How did I see that? Well, I tried hooking up the supremely useful SQL Profiler to my ISP's database that was holding the data, but I didn't have permission. Luckily, the SQL tab in LinqPad will show me what SQL is being executed and it showed me just that (or rather, the slightly more verbose and more correct SQL that LINQ to Entities generates in these circumstances).

Now, I had a problem. I didn't want to pass around IEnumerable, because clearly that's slowing things down. A lot. On the other hand, I don't want to use ObjectSet<Post> because it doesn't compose, i.e. Where doesn't return that. What is the right interface to use to compose separate expressions into a single SQL statement? As you've probably guessed by now from the title of this post, the answer is: IQueryable.

Unlike IEnumerable, IQueryable exposes the underlying expression so that it can be composed by the caller. In fact, if you look at the IQueryable implementation of the Count extension method, you'll see something very different:

public static int Count<TSource>(this IQueryable<TSource> source) {
  ...
  return source.Provider.Execute<int>(
    Expression.Call(null,
      ((MethodInfo) MethodBase.GetCurrentMethod()).
      MakeGenericMethod(
        new Type[] { typeof(TSource) }),
        new Expression[] { source.Expression }));
}

This code isn't exactly intuitive, but what's happening is that we're forming an expression which is composed of whatever expression is exposed by the IQueryable we're operating over and the Count method, which we're then implementing. To get this code path to execute for our example, we simply have to replace the use of IEnumerable with IQueryable:

IQueryable<Post> FilterByCategory(IQueryable<Post> posts, string category) {
  if( !string.IsNullOrEmpty(category) ) {
    return posts.Where(p => p.Category.Contains(category));
  }
}
...
  var posts = FilterByCategory(db.Posts, category);
  int count = posts.Count();
...

Notice that none of the actual code changes. However, this new code runs much faster and with the case- and null-insensitivity built into the 'like' operator in SQL instead of semantics of the Contains method in LINQ to Objects.

The way it works is that we stack one IQueryable implementation onto another, in our case Count works on the Where which works on the ObjectSet returned from the Posts property on the object context (ObjectSet itself is an IQueryable). Because each outer IQueryable is reaching into the expression exposed by the inner IQueryable, it's only the outermost one -- Count in our example -- that causes the execution (foreach would also do it, as would ToList() or ToArray()).

Using IEnumerable, I was pulling back the ~3000 posts from my blog, then filtering them on the client-side and then doing a count of that.With IQueryable, I execute the complete query on the server-side:

select count(*) from Posts where Category like '%whatever%'

And, as our felon friend Ms. Stewart would say: "that's a good thing."

12 comments



Friday, Apr 2, 2010, 10:37 AM

College info for my sophomore

I went to a college planning sessions at my sons' high school not because I'm hung up on getting my Sophomore into a top school, but because I thought I'd get a jump on things. I learned I was actually behind.

For one, I learned that the high school has an online system that will do some amazing things:

That means that my son can answer questions about personality and interests and draw a straight line through to what he needs to do to get into a school so he can learn to do the jobs he'll like and be good at. Holy cow. We didn't have anything like that when I was a kid.

Further, the online system has two complete SAT and ACT tests in it, so, along with the PSAT that he's already taking, he can do a practice ACT, figure out which test he's best at (my 34 ACT score was way better than my 1240 SATs) and just take that test, since most schools these days take both SAT or ACT results.

This is all freely provided by the high school and, in fact, they have counseling sessions with the students at each grade level for them to get the most from this system.

It's no wonder that 93% of students from this high school go on to 4 or 2-year college degree programs.

That was the good part.

The scary part is that my eldest, half way through his Sophomore year, is essentially half-way through his high school career. Colleges only see their grades through the end of Junior year, since most college applications are due in the middle of January of their Senior year at the latest. I have to sit down with my son and have the conversation about how "even if you get a 4.0 from now on, the best grades you can have are..."

Is it just me or is the world moving faster with each passing day?

3 comments



Saturday, Mar 27, 2010, 1:53 PM

Updated the CsvFileTester for Jet 4.0

I was playing around building a tool to let me edit a database table in Excel, so I updated my CvsFileTester project to work in a modern world, including the 32-bit only Jet 4.0 driver you've probably go lying around on your HD.

Enjoy.

7 comments



Sunday, Mar 21, 2010, 1:40 PM

you may experience some technical difficulties

I've been futzing with the site and I've got more to do, so unexpected things may happen. Last weekend I screwed with the RSS generator and that caused a bunch of folks to see RSS entries again. This weekend I'm moving more of my static content into the database, so you may see a bunch of old stuff pop up.

Feel free to drop me a line if you see anything you think needs fixing. Thanks for your patience.

1 comment



Thursday, Mar 18, 2010, 7:59 AM

On Building a Data-Driven E-Commerce Site

The following is a preprint of an article for the NDC Magazine to be published in Apri.

 

It had been a long, hard week at work. I had my feet up when a friend called and popped the question: “Do you know how to build web sites?”

 

That was about a month ago and, after swearing to her that I spent my days helping other people build their web sites, so I should oughta know a thing or two about how to build one for her. After some very gentle requirements gathering (you don’t want a bad customer experience with a friend!), I set about designing and building bestcakebites.com, a real-world e-commerce site.

 

 

She didn’t need a ton of features, just some standard stuff:

·        Built on a technology I already knew so I could have the control I needed.

·        Listing a dozen or so products with pictures and descriptions.

·        A shopping cart along with, ideally, an account system so folks could check their order status or reorder easily.

·        Shipping, handling and tax calculation.

·        Taking payment.

·        Sending email notifications of successful orders to both the customer and the proprietor.

 

As it turns out, there are a bunch of ways to skin this particular cat, but because I was a busy fellow with a more-than-full-time job and a book I’m supposed to be writing, instead of falling prey to my engineering instinct to write my own website from scratch, I decided to see what was out there.

 

As it turns out, there’s quite a few e-commerce web site solutions in the world, several of them recommended by PayPal, as well as one that PayPal itself provides, if you don’t mind sending shoppers to their web site. And if fact, I did. Requirement #1 was that I needed complete control over the code and the look and feel of the site. I didn’t want to configure somebody else’s web site and risk going off of her chosen domain name or not being able to tweak that one little thing that meant the difference between #succeed and #fail. (Friend customers are so picky!)

 

The e-commerce solution I picked was the one I found on http://asp.net (I am a Microsoft employee after all): nopCommerce. It’s an open source solution based on ASP.NET and CSS, which meant that I had complete control when it wasn’t perfect (control I used a few times). It was far more than full-featured enough, including not only a product database, a shopping cart, shipping calculation and payment support, but also categories and manufacturers, blogs, news and forums, which I turned off to keep the web site simple (and to keep the administration cost low). Unexpected features that we ended up liking included product variants (lemon cake bites in sets of 8, 16 and 24 made up three variants, each with their own price, but sharing a description), product reviews, ratings and site-wide search.

 

The real beauty of nopCommerce, and the thing that has been the biggest boon, was that the whole thing is data-driven from SQL Server. To get started, I ran the template web site that was provided, it detected that it had no database from which to work and created and configured the initial database for me, complete with sample data. Further, not only was it all data-driven based on the products, orders and customers the way you’d expect, but also on the settings for the web site behavior itself.

 

For example, to get shipping working, I chose from a number of built-in shipping mechanisms, e.g. free, flat rate, UPS, UPSP, FedEx, etc., and plugged in my shipper information (like the user name and password from my free usps.com shipping calculation web service account)

 

With this configuration in place, the next order the site took, it used that shipper, pulling in the shipping information from the set of size and weight measurements on the ordered products (from the database), calling the web service as it was configured (also from the database) to pull in the set of shipping options from that shipper, e.g. Express Mail, Priority Mail, etc., augmenting the shipping prices with the per product handling changes, and letting the user pick the one they wanted. All I had to do was use the administration console, tag each product with size information and tell nopCommerce that I’d like USPS today, please.

 

Everything worked this way, including tax calculation, payment options (we chose PayPal Direct and Express so that folks with a credit card never left our site whereas folks with PayPal logged into their account on the familiar paypal.com), localization, whether to enable blogs, news, forums, etc. Most of the time when I wanted to make a change, it was just a matter of flipping the right switch in the database and not touching the code at all.

 

As one extreme example of where the data-driven nature really came through was on the order numbers generated by the site. During testing, I noticed that our order numbers were monotonically increasing from 1. Having ordered from a competitor’s site, their order number was only 103, clearly showing off what amateurs they were (and the order itself took a month to arrive after two pestering emails, so it was clear how amateur they really were). I didn’t want us to appear like newbies in our order-confirmation emails (which nopCommerce also generated for us), so I found the Nop_Order table, and used SQL to increase the identity column seed, which it was clear was the origin of the order number: 

DBCC CHECKIDENT (Nop_Order, RESEED, 10047)

From then on, every time an order came through, we protected experience simply because of the order number, which I changed without touching a line of code. If helping you “fake it ‘til you make it” isn’t enough reason to love a data-driven solution, I don’t know what is!

0 comments



Thursday, Mar 11, 2010, 11:21 AM

The incomplete list of impolite WP7 dev requests

In my previous list of WP7 user requests, I piled all of my user hopes and dreams for my new WP7 phone (delivery date: who the hell knows) onto the universe as a way to make good things happen. And all that’s fine, but I’m not just a user; like most of my readers, I’m also a developer and have a need to control my phone with code. I have a long list of applications I want to write and an even longer list of applications I want other developers to write for me.

 

Today at 1:30p is the first public presentations of how to do WP7 programming, so to affect the future, I have to get my feature requests for the Windows Phone 7 Series development environment posted now!

 

·        I want the legendary Microsoft tools for code editing, UI design, debugging, deployment, version control, add-ins, project management, etc. Please just let me install the “Windows Phone 7 Series SDK” and have Dev10 light up with new project and project item templates et al.

·        I definitely want to be able to write C#. Since Charlie’s mentioned Silverlight, it seems like I’ll be able to do just that.

·        I want to be able to mark a program as useful for background processing, e.g. I’m writing Pandora, and let that trigger a question for the user as to whether to allow it or not, ideally with a message like “Pandora would like to continue to run in the background using XX% of your battery. Is that OK?”

·        For most apps that would like to appear as if they’re running in the background, I want to register a bit of code to run when its own cloud-based notifications comes in, e.g. an new IM or sports score.

·        I want to be able to access data from built-in apps, e.g. contacts, appointments, etc.

·        Obvious things:

o   Notification when the user switches orientation

o   Access to the compass, GPS, network, camera, mic, etc.

o   Access to the network using TCP, HTTP, Atom, AtomPub and OData.

o   Low and high-level access to gestures

o   A nice set of build-in standard controls, including simple things like text box and more complicated things like map and route

o   Integration with existing apps, e.g. the ability to launch the map app from my own app at a specific location or to a specific route.

o   Ability to create custom controls/do custom drawing.

o   Serialization so I can keep user data between sessions. Notifications when my app is being whacked.

o   App-selected keyboards for specific tasks, e.g. entering a URL.

 

That doesn’t seem like a very big list. I must be missing something. : )

2 comments



Tuesday, Mar 9, 2010, 1:47 PM

Creating a Lazy Sequence of Directory Descendants in C#

My dear friend Craig Andera posted an implementation of a function that descends into a directory in a "lazy" manner, i.e. you get the first descendant back right away and not after all descendants have been calculated. His implementation was in Clojure, a Lisp variant that runs on the Java VM:

(import [java.io File])

(defn dir-descendants [dir]
  (let [children (.listFiles (File. dir))]
    (lazy-cat
     (map (memfn getPath) (filter (memfn isFile) children))
     (mapcat dir-descendants
      (map (memfn getPath) (filter (memfn isDirectory) children))))))

Craig was happy with this function because, even though it was a "mind-bender to write," it's easy to read and because C# "would almost certainly be at least somewhat more verbose."

Taking this as a challenge, I rewrote this program in C#, maintaining the laziness:

using System.IO;
using System.Collections.Generic;

namespace ConsoleApplication1 {
    class Program {
        static IEnumerable<string> GetDirectoryDecendants(string path) {
            foreach (var file in Directory.GetFiles(path)) { yield return file; }
            foreach (var directory in Directory.GetDirectories(path)) {
                foreach (var file in GetDirectoryDecendants(directory)) { yield return file; }
            }
        }
    }
}

The key hit here is the use of "yield return" which lets me return elements of an IEnumerable as I calculate them. This took me 5 minutes to write, my mind is straight and I find it fairly easy to read. I'll let you decide on the relative verbosity of each implementation.

18 comments



Tuesday, Mar 9, 2010, 11:25 AM

The incomplete list of impolite WP7 user feature requests

When I first moved from the combination of a dumb phone and a separate music player, I had modest requirements: phone calls, MP3 playback, calendar notifications, contact management, email, camera and solitaire. Even asking for only these seven things, my first smart phone was as life changing as my first laptop. I could do a great deal of my work while out and about, allowing me to have a much more productive work/personal life balance.

 

When I was first married, the word “love” didn’t seem big enough for what I felt for my bride. These days, the word “phone” doesn’t seem nearly big enough for the pocket-sized mobile device that I’m never without, like my wallet and my keys. Further, I expect my phone to replace my wallet and keys any day now, along with the Walkman, DVD player, TV, radio, book shelf, notepads, calculator, compass, alarm clock, wall calendar, newspaper, encyclopedia, dictionary, GameBoy, carpenter’s level, laptop, navigation device and landline it’s already replaced.

 

Now that I’ve been through several smart phones, including my favorites, the T-Mobile Dash and the iPhone 3G, I have a much longer, incomplete list of what I want from my Windows Phone 7 Series (and I know it’s incomplete because after I post this list, someone is going to remind me what vital things I missed : ).

 

·        A calculator. It’s surprising how useful this is, including the scientific features.

·        A battery that lasts at least 24 hours while I’m using Bluetooth, 3G, Wi-Fi, GPS, music and my apps. Oh, and please let me charge the thing with a standard connector (USB!) and let me use my phone while it’s recharging.

·        An easy, high-quality way to run the music through my car stereo. The Sells Brothers and I like to jam!

·        An easy way to switch back and forth to airplane mode. Or even better, can you make it so the device isn’t an FAA threat during takeoff and landing so I can stop reading the stupid magazine in the seat pocket in front of me for 5 minutes at the beginning and ending of my flights?

·        Great auto-correct on my hard or soft keyboard entry. This is really the only way that allows my big fingers and the lack of tactile feedback to even work with a phone keyboard.

·        Copy-paste: I can’t live w/o it anymore. Also, please include pasting into my phone during calls so I can stop memorizing 9-digit conference call IDs.

·        I’d really love intelligent integration of music, i.e. keep it playing when I switch apps and not just the built-in Zune player, but 3rd party music apps, too (aka Pandora). Also, let me pause, next, previous while my phone is locked or I’m in another app. Finally, make sure to stop music when I get a call and start it back up again when my call is over. I love that.

·        Full (!) calendar support:

o   Sync’ing with Exchange and not Exchange.

o   Recognition of phone numbers and addresses in my calendar appointments with links to dial/get directions.

o   Reply All to an appointment so that I can let folks know I’m running late.

o   Snooze on my meeting reminders (I can’t tell you how many times I’ve forgotten my meeting after the one and only 15 minute reminder).

o   Show my appointments on my home page instead of making me dig into some app.

·        Please provide a responsive UI, even if I haven’t rebooted in a week. Ideally I’d never have to reboot at all.

·        Wireless sync’ing to my PC. My house is bathed in Wi-Fi; why make me connect a wire?

·        Tethering so I can use my phone as a network connection for my PC. I’m paying for unlimited data – let me use it! And ideally make that wireless, too.

·        Turn-by-turn directions! This won’t be ready until I go off course and I hear “recalculating” from my phone piped through my car stereo with Pandora playing in the background.

·        There definitely needs to be an "app store" for phone apps, but also there needs to be a way to install apps from other sources without hacking my phone. Also, please let me install them on my SD card so I can take advantage of the extra memory.

·        Let me install extra memory!

·        Let me replace the battery! Batteries go bad over time and they need to be replaced on the go.

·        I need a great audio book listening experience (bookmarks!) and a great ebook reading experience (formats!).

·        I’d like some phone-wide search, including the ability to see where the result came from. I never want the email-only Contact from the list of everyone that I’ve ever received an email from – I want the real contact info that I’ve got cached on my phone.

·        Full contact lookup, both personal and corporate (Exchange).

·        Good camera (and flash): the one on my phone is the only one I ever use, as it’s the one I always have with me.

·        Bluetooth and voice dialing for hands free operation (required by state law in both Washington and Oregon, where I spend most of my time). Also, I’d love the same integration with my Jawbone that I have with my iPhone, i.e. volume control and battery indicator.

·        Apps I can’t live without:

o   Evernote: I’m willing to move my data into OneNote so long as I can sync between the web, my phone and my PC.

o   Social networking clients: IM, Twitter, an RSS/ATOM Feed Reader, YouTube and Facebook.

o   Converter for currency, distance, volume, etc.

o   A Compass.

o   A Flashlight. I have used the ambient life from my phone to get myself out of the forest in pitch blackness. Without it, I’m sure I would’ve been hacked to pieces by Jason or Michael Meyers.

o   TripIt, Movies, OpenTable, UrbanSpoon, Mint: I use these all the time.

o   Shazam: Before this app, I used to record snippets of songs and email them to my son would be charge me $.50/ea. to find the title and artist so I could grab them for my phone. Shazam has cut out the middle man and represents ~100% of the music I purchase these days.

o   Skype or some other good way to use my phone to do IP Telephony (or even IP Video Conferencing)

o   Tetris! I guess there are other casual games in the world, but that’s mine.

 

Because the WP7 hasn’t shipped yet, I can pile all of my hopes and dreams on it and, like everyone else not on the WP7 team, I have very little idea of whether my hopes will be fulfilled, but that doesn’t stop me from dreaming. So now it’s your turn – what did I miss? : )

 

P.S. I know that lots of phones have a subset of these features and I’m sure someone will tell me that, with the correct config, I can make their favorite phone do all these things. I know that’s going to happen because whenever I complain about a missing feature in the Visual Studio editor, some emacs guy says, “Oh, you can do that with Alt+Shift+Left Elbow in my editor!” I don’t care about what your phone can do. No phone’s UI has stirred me like the WP7’s UI. That’s the one I want to use, so that’s the phone I’m going to bang on ‘til my incomplete list is complete.

5 comments



Friday, Mar 5, 2010, 4:19 PM

"Deep Fried Bytes Podcast": Lars on SQL Server Modeling

Here's how the Deep Fried guys describe episode 45: "At PDC 2009, 'Oslo' was renamed to SQL Modeling and it left a lot of developers scratching their heads. What better way to sort it all out than to talk with someone deep into the stack. We sat down with Lars Corneliussen to see how this is all going to turn out and it what it means for developers. Definitely an interesting show as it paints a different picture about where things are going with 'M', 'M' Grammar, SQL modeling, Entity Framework, Quadrant and so on." Check it out!

0 comments



Thursday, Mar 4, 2010, 10:13 AM

SQL Server Modeling CTP (November 2009 Release 2)

An update of the SQL Server Modeling CTP (November 2009) that's compatible with Visual Studio 2010 RC has been released on the Microsoft Download Center. This release is strictly an updated version of the original November 2009 CTP release to support Visual Studio 2010 and .NET Framework 4 RC. It contains no other fixes outside of those required to work with the new RC. Enjoy!

1 comment



Wednesday, Mar 3, 2010, 5:21 PM

Please don't run apps in the background on my WP7 phone!

When I was but a wee lad, I learned that when it came to my computer, I was often going to be waiting on something, whether it was the CPU, the IO or the memory. Now that I'm all grown up and spending a great deal of time on handheld mobile devices, I've discovered a whole new thing I'm waiting on: charging the battery.

In the bad old days of DOS, I spent a disturbing amount of time working on my autoexec.bat and config.sys files to optimize the loading of drivers and TSRs (DOS programs that run in the background for you whippersnappers). Now, instead of optimizing for memory usage on my PC,  I spend my time optimizing for power consumption on my phone, e.g. turning off 3G and Bluetooth when I don't need them, turning down the polling frequency on my SMTP mail accounts and spreading power adapters everywhere in my world where I sit for more than 5 minutes. The single most important feature on my phone is that's it's on and the way power is managed on my iPhone means that this is often not the case. Sometimes I pine for my Windows Mobile Dash for just that reason; it ran for days instead of hours.

And as bad as this power situation is, it would be even worse if my phone ran more than one app at a time. I don't worry about random apps from the AppStore using too much memory or crashing; I worry about them eating my battery and killing my iPhone in the middle of a route to somewhere I've never been. By not allowing background apps to run, Apple is trying to do the right thing but (although my battery life still sucks). I don’t have personal experience with Google phones, but since they do allow background apps to run, I have to imagine battery life is an even bigger problem.

So, when I see people lobbying for background apps on the new Windows Phone 7 Series, all I can say is, you don't want it. What you want is for work to go on in the background for you without the cost in power.

Oh, I want to listen to my MP3s or Pandora while I answer my email like everyone else, but I don't want every financial/IM/email/social/sports app I download sucking down my battery life because it feels itself to be more important than everything else on my phone. I want those apps to notify me when something I care about happens but I don't want the processing to discover such events to happen on my phone - I want the processing to happen in the cloud.

You may recall my piece about how important storage in the cloud is for moble devices. Let's let somebody else scale and manage the storage so we can leverage it. In the same way, we want to leverage CPU and power in the cloud, saving local resources for cool graphics, twitch games and streaming my "Pink" channel.

Of course, if we're going to push the processing to the cloud, I'm going to need an efficient and easy way to write my WP7 apps to be notified so I can do the actual processing that needs to happen on the phone. And that all needs to happen while I'm navigating and playing my bad girls party mix.

I'm saving my WP7 phone battery for important things after all.

22 comments



Monday, Feb 22, 2010, 11:31 PM

Update for SQL Server Modeling CTP and Dev10 RC

We are currently preparing a release of the SQL Server Modeling November 2009 CTP that will install and operate with Visual Studio Release Candidate. We expect to make this release available the first week of March and will make an announcement here at that time.

We are also planning for another release of the November CTP that matches the final Visual Studio product (RTM) when that product becomes generally available.

0 comments



Monday, Feb 15, 2010, 2:23 PM

Windows Phone Series 7 Link Roundup

I was swamped this morning, so didn't get to see the Windows Phone Series 7 stuff live. When I did finally get to poke my head out, Scott Stanfield and Damir Tomicic had the list of links all set for me to follow. Thanks, guys!

Now I just have to let my AT&T contract run out and find a buyer for my iPhone. Can't wait!

0 comments



Tuesday, Feb 9, 2010, 5:55 PM

Entity Designer Database Generation Power Pack

If you like Model-First design in Entity Framework, you're going to love the Entity Designer Database Generation Power Pack. The original Database Generation feature in the Entity Designer in VS 2010 is extensible via Windows Workflows and T4 Templates. This Power Pack builds on these extensibility mechanisms and introduces the following:

Highly recommended. Enjoy!

2 comments



Sunday, Feb 7, 2010, 12:02 PM

Data Binding, Currency and the WPF TreeView

I was building a little WPF app to explore a hierarchical space (OData, if you must know), so of course, I was using the TreeView. And since I'm a big fan of data binding, of course I've got a hierarchical data source (basically):

abstract class Node {
  public abstract string Name { get; }
  public abstract IEnumerable<Node> { get; }
  public XDocument Document { get { ... } }
  public Uri Uri { get { ... } }
}

I then bind to the data source (of course, you can do this in XAML, too):

// set the data context of the grid containing the treeview and text boxes
grid.DataContext = new Node[] { Node.GetNode(new Uri(uri)) };
// bind the treeview to the entire collection of nodes
leftTreeView.SetBinding(TreeView.ItemsSourceProperty, ".");
// bind each text box to a property on the current node
queryTextBox.SetBinding(TextBox.TextProperty,
  new Binding("Uri") { Mode = BindingMode.OneWay });
documentTextBox.SetBinding(TextBox.TextProperty,
  new Binding("Document") { Mode = BindingMode.OneWay });

What we're trying to do here is leverage the idea of "currency" in WPF where if you share the same data context, then item controls like textboxes will bind to the "current" item as it's changed by the list control. If this was a listview instead of a treeview, that would work great (so long as you set the IsSynchronizedWithCurrentItem property to true).

The problem, as my co-author and the-keeper-of-all-WPF-knowledge Ian Griffiths reminded me this morning, is that currency is based on a single collection, whereas a TreeView control is based on multiple collections, i.e. the one at the root and each one at sub-node, etc. So, as I change the selection on the top node, the treeview has no single collection's current item to update (stored in an associated "view" of the data), so it doesn't update anything. As the user navigates from row to row, the "current" item never changes and our textboxes are not updated.

So, Ian informed me of a common "hack" to solve this problem. The basic idea is to forget about the magic "current node" and explicitly bind each control to the treeview's SelectedItem property. As it changes, regardless of which collection from whence the item came, each item control is updated, as data binding is supposed to work.

First, instead of setting the grid's DataContext to the actual data, shared with the treeview and the textboxes, we bind it to the currently selected treeview item:

// bind the grid containing the treeview and text boxes
// to point at the treeview's currently selected item
grid.DataContext = new Binding("SelectedItem") { ElementName = "leftTreeView" };

Now, because we want the treeview to in fact show our hierarchical collection of nodes, we set it's DataContext explicitly:

// set the treeview's DataContext to be the data we want it to show
leftTreeView.DataContext = new Node[] { Node.GetNode(new Uri(uri)) };

Now, the treeview will show the data we wanted it to show, as before, but as the user changes the selection, the treeview's SelectedItem property changes, which updates the grid's DataContext, which signals the textboxes, bound to properties on grid's DataContext (because the DataContext property is inherited and we haven't overridden it on the textboxes), and the textboxes are updated.

Or, in other words, the textboxes effectively have a new idea of the "current" item that meshes with how the treeview works. Thanks, Ian!

0 comments



Thursday, Feb 4, 2010, 9:01 PM

Telerik LINQ to M Refresh for Nov09 Modeling CTP

The Telerik LINQ to "M" implementation allows developers to use LINQ statements with blocks of "M" values, pure text or the results of a transformed DSL. With the new SQL Server Modeling November 2009 CTP there are some changes to the "M" specification, so Telerik has updated their core DLLs to accommodate these changes. Enjoy!

0 comments



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