Linq to SQL Stored Procedures with Multiple Results

Question

We have followed the approach below to get the data from multiple results using LINQ To SQL

CREATE PROCEDURE dbo.GetPostByID
(
    @PostID int
)
AS
    SELEC         


        

Answer 1

Heya dude - does this work?

IEnumerable<Post> posts;
IEnumerable<Category> categories;

using (BlogContext ctx = new BlogContext(...))
{
    ctx.DeferredLoadingEnabled = false; // THIS IS IMPORTANT.
    IMultipleResults results = ctx.GetPostByID(...);
    posts = results.GetResult<Post>().ToList();
    categories = results.GetResult<Category>().ToList();
}
// Now we need to associate each category to the post.
// ASSUMPTION: Each post has only one category (1-1 mapping).
if (posts != null)
{
    foreach(var post in posts)
    {
        int postId = post.PostId;
        post.Category = categories
            .Where(p => p.PostId == postId)
            .SingleOrDefault();
    }
}

Ok. lets break this down.

First up, a nice connection inside a using block (so it's disposed of nicely).

Next, we make sure DEFERRED LOADING is off. Otherwise, when u try and do the set (eg. post.Category == blah) it will see that it's null, lazy-load the data (eg. do a rountrip the database) set the data and THEN override the what was just dragged down from the db, with the result of there Where(..) method. phew! Summary: make sure deferred loading is off for the scope of the query.

Last, for each post, iterate and set the category from the second list.

does that help?

EDIT

Fixed it so that it doesn't throw an enumeration error by calling the ToList() methods.

Answer 2

Just curious, if a Post have have one or many Categories, is it possible to instead of using the for loop, to load the Post.PostCategories with the list of Categories (one to many), all in one shot, using a JOIN?

var rslt = from p in results.GetResult<Post>()
           join c in results.GetResult<Category>() on p.PostId = c.PostID
           ...
           p.Categories.Add(c)

Answer 3

Scott Guthrie (the guy who runs the .Net dev teams at MS) covered how to do this on his blog some months ago much better than I ever could, link here. On that page there is a section titled "Handling Multiple Result Shapes from SPROCs". That explains how to handle multiple results from stored procs of different shapes (or the same shape).

I highly recommend subscribing to his RSS feed. He is pretty much THE authoritative source on all things .Net.