CODEWITHSUNDEEP
linqc#-3.0subsonic-v3p2
Nesizer
Nesizer

Reputation: 3214

linq help - newbie

how come this work 

public IQueryable<Category> getCategories(int postId)  
{
      subnusMVCRepository<Categories> categories = new subnusMVCRepository<Categories>();
      subnusMVCRepository<Post_Category_Map> postCategoryMap = new  subnusMVCRepository<Post_Category_Map>();

      var query = from c in categories.GetAll()
                  join pcm in postCategoryMap.GetAll() on c.CategoryId equals pcm.CategoryId
                  where pcm.PostId == 1
                  select new Category
                  {
                    Name = c.Name,
                    CategoryId = c.CategoryId
                  };
       return query;
}

but this does not

public IQueryable<Category> getCategories(int postId)  
{
subnusMVCRepository<Categories> categories = new subnusMVCRepository<Categories>();
subnusMVCRepository<Post_Category_Map> postCategoryMap = new subnusMVCRepository<Post_Category_Map>();

    var query = from c in categories.GetAll()
                join pcm in postCategoryMap.GetAll() on c.CategoryId equals pcm.CategoryId
                where pcm.PostId == postId
                select new Category
                {
                    Name = c.Name,
                    CategoryId = c.CategoryId
                };
    return query;
  }

Upvotes: 0

Views: 224

Answers (2)

cosullivan
cosullivan

Reputation:

The issue is most likely in the implementation of the query provider.

pcm.PostId == 1

and

pcm.PostId == postId

actually have a big difference. In the expression tree the first is generated as a ConstantExpression which doesnt need to be evaulated.

With the second, the compiler actually generates an inner class here (this is the _DisplayClassX that you see). This class will have a property (will most likely be the same name as your parameter) and the expression tree will create a MemberAccessExpression which points to the auto-generated DisplayClassX. When you query provider comes accross this you need to Compile() the Lambda expression and evaluate the delegate to get the value to use in your query.

Hope this helps.

cosullivan

Upvotes: 3

Alexandre Brisebois
Alexandre Brisebois

Reputation: 6743

The problem is not the linq itself, you need to be sure that the context or provider object is able to fetch the data. try testing the 

subnusMVCRepository<Categories> categories = new subnusMVCRepository<Categories>();
subnusMVCRepository<Post_Category_Map> postCategoryMap = new subnusMVCRepository<Post_Category_Map>();

objects and see if they are populated or if they behaving as required.

you may want to search the generated code for c__DisplayClass1 and see what you can see there. some times the generated code dose some weird things.

when you step into you code check the locals and the variable values. this may also give you some clues.

Edit : Have you tried to return a List<> collection ? or an Enumerable type?

Edit : What is the real type of the item and query may not be iterable

Upvotes: 0

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