ASP.NET Debugging : Linq

ASP.NET Troubleshooting

Tom — Tue, 24 Mar 2009 19:31:03 GMT

So with how long ASP.NET has been out for now, I am really curious to know how people go about tracking down issues in their project.

I’d like to know things like:

How do you know there is a problem
What tools do you use to confirm that the problem really is a problem
How do you gather data about the problem
How do you determine if the problem is your code or something else (like the network, hard drive failure, etc)
If the problem is your code, how do you ensure your fix resolves the problem (how do you test the fix)

If there are any others, I’d also like to hear them.

Also, if you do anything in the Cloud now, I’d love to hear how you troubleshoot that. And it can be from any cloud service provider.

And have any of these things changed with some of the new ways to program that have come out. For example, AJAX, MVC, Silverlight, IE8, jQuery, etc.

Linq exception

Tom — Wed, 25 Feb 2009 18:44:15 GMT

If you have done much programming with Linq and using the relationships between tables, you may come across the following exception:

System.Data.Linq.ForeignKeyReferenceAlreadyHasValueException
Operation is not valid due to the current state of the object.

This is basically telling you that you have a Relationship between two tables and you are trying to update the link to point to something else.

In my case, I had something like:

Table1

ID
nvarchar

Table2

ID
Table1ID

And I was setting Table1ID, which maps to Table1’s ID to 0. So if you want to delete an entry, just remove the row in Table1 and Table2 will be updated with the delete.

Linq features to make smaller code

Tom — Fri, 12 Dec 2008 17:50:53 GMT

I have been working on some code that involves using Linq to query a database and came across something that I thought was really useful. So here is the situation:

We have a query that we want to be able to sort in multiple ways. This will allow the user to click on columns and sort by it. That kind of thing. The first way that I did this was to do something like the following:

if (sortmethod.CompareTo("date") == 0)
{
    var c = from p in db.ProductSales
            from t in db.Products
           where (t.Id == p.ProductId)
           group t by t into g
           orderby g.Count() descending
           select g;
} else {
    var c = from p in db.ProductSales
            from t in db.Products
           where (t.Id == p.ProductId)
           group t by t into g
           orderby g.Key
           select g;
}

This can get very long if you have multiple things that someone can sort by. So after doing some digging around, I found an alternative way that you can do this which is much shorter and much easier to follow:

var c = from p in db.ProductSales
            from t in db.Products
            where (t.Id == p.ProductId)
            group t by t into g
            select g;

switch (sortmethod)
{
    case "date":
        c = c.OrderByDescending(g => g.Count());
        break;
    default:
        c = c.OrderBy(g => g.Key);
        break;
}

As you can see, this now allows us to just do the sorting based on what the user wants but the rest of the query doesn’t have to be redone. This can save a lot of code and effort for development and testing. Plus, you can imagine if there is a change to the database, in the first method, you would have to change the Linq query for each sort. Where in the second method, you change it once and that is all.

Hope this is useful and happy coding.

Linq – Do we need another way to access databases?

Tom — Mon, 20 Oct 2008 13:00:00 GMT

This was the question that was burning on my mind when I first heard about Linq. I was skeptical and didn’t think it was something that we needed. But after having started to use this new language, I have quickly become a believer.

Linq stands for language-integrated query and that is exactly what it is, it allows for rich metadata, compile-time syntax checking, static typing and IntelliSense on things that used to be imperative code. This is not only a huge win from the error perspective, but also from the ease of use one.

For example, here is a sample query which includes populating an array to store the data:

     using System;

    using System.Linq;

    using System.Collections.Generic;

    class app {

      static void Main() {

        string[] names = { "Burke", "Connor", "Frank", 

                           "Everett", "Albert", "George", 

                           "Harris", "David" };

        IEnumerable<string> query = from s in names 

                                   where s.Length == 5

                                   orderby s

                                   select s.ToUpper();

        foreach (string item in query)

          Console.WriteLine(item);

      }

    }

You can see where we query the data, you just simply do something like “from s in names where s.Length == 5 orderby s select s.ToUpper();” This clearly is close enough to SQL that anyone with experience with SQL programming will understand it and get used to doing this, but this means that if there is a typo, or any other problem in the query, you will find it at compile time.

Linq to SQL

For SQL, there are some specific things built into Linq. You can read all about it here. The main thing to know is that there is a DataContext object which does most of the interaction for you. If you are in Visual Studio and create a Linq to SQL object in there, you can point it to any/all of your tables and then access them in a very Object Oriented manner. And when you are done changing/inserting things into the database, simply call DataContextInstance.SubmitChanges() and it will take care of updating things.

This is a very powerful and intuitive language and I am just starting to wrap my head around it. Hope that this makes you want to try it out also and see what you think.