The “X” property on “Y” could not be set to a 'null' value. You must set this property to a non-null value of type 'Int32'

Question

When I run my application and I click a specific button I get the error:

\"The \"X\" property on \"Y\" could not be set to a \'null\' value. You must set thi         


        

Answer 1

For future readers.

I got this error when I had a multiple result stored procedure.

As seen here:

http://msdn.microsoft.com/en-us/data/jj691402.aspx

If you try to access an item in the first-result, after doing a .NextResult, you may get this error.

From the article:

    var reader = cmd.ExecuteReader();

    // Read Blogs from the first result set
    var blogs = ((IObjectContextAdapter)db)
        .ObjectContext
        .Translate(reader, "Blogs", MergeOption.AppendOnly);   


    foreach (var item in blogs)
    {
        Console.WriteLine(item.Name);
    }        

    // Move to second result set and read Posts
    reader.NextResult();
    var posts = ((IObjectContextAdapter)db)
        .ObjectContext
        .Translate(reader, "Posts", MergeOption.AppendOnly);


    foreach (var item in posts)
    {
        Console.WriteLine(item.Title);
    }

Now, if before the line

foreach (var item in posts)

you put in this code

Blog foundBlog = blogs.FirstOrDefault();

I think you can simulate the error.

Rule of Thumb:

You still gotta treat this thing like a DataReader (fire-hose).

For my needs, I had to convert to a List<>.

So I changed this:

    foreach (var item in blogs)
    {
        Console.WriteLine(item.Name);
    }  

to this:

    List blogsList = blogs.ToList();
    foreach (var item in blogsList )
    {
        Console.WriteLine(item.Name);
    }  

And I was able to navigate the objects without getting the error.

Here is another way I encountered it.

    private void DoSomething(ObjectResult blogs, ObjectResult posts)
    {

    }

And then after this code (in the original sample)

foreach (var item in posts)
{
    Console.WriteLine(item.Title);
}

put in this code:

DoSomething(blogs,posts);

If I called that routine and started accessing items/properties in the blogs and posts, I would encounter the issue. I understand why, I should have caught it the first time.