Question

I am working on making an entity framework project more scalable to suit our requirements. The project uses an EDMX file, Entity Framework, and .NET 4.0. The project has globally setup lazy loading.

Basically, I have 2 tables:

Product
  ProductId

ProductVariant
  ProductVariantId
  ProductId

I have a situation where there will be hundreds of thousands of related rows in ProductVariant for a given Product. So I would like to remove the navigation property for ProductVariant and make a query to lookup only the most pertainant data, rather than all of the related data.

However, most of the code does something like:

if (Product.HasVariants) { [Loop Through Variants And Do Something] }

Which I will change to:

if (Product.HasVariants) { [Lookup Subset of Variants from DB And Do Something] }

HasVariants is a method that currently looks like this:

public bool HasVariants()
{
    return this.Variants.Count > 0;
}

Variants is a navigation property. What I would like to do is create a lookup query with a field indicating whether any related data exists in the variants table rather than calling the database every time the code does this check.

This is how I would accomplish this in a stored procedure:

CREATE Procedure GetProduct
  @ProductId
AS

Declare @HasVariants bit

Set @HasVariants = EXISTS(Select ProductVariantId 
                          From ProductVariant 
                          Where ProductId = @ProductId)

SELECT ProductId, <Other Fields>, @HasVariants AS HasVariants
FROM Product
WHERE ProductID = @ProductID

Return

Note the presence of the HasVariants field, which I would use in the HasVariants method instead of the collection.

My question is how do I accomplish the same thing (a lookup field from a related table) using an EDMX based model? I want to do this without using SQL statements in the code, but if the solution involves making HasVariants into a navigation property (possible?) it is acceptable. I already understand how to write a query to execute on demand, what I am looking for is a way to make the entity framework cache the HasVariants property the same way it does for the rest of the product data.

Forgive me if I didn’t provide enough information. I am new to the Entity Framework and I am really not sure what is needed to answer this question.

Answer 1

If you want to duplicate your stored procedure you will need to create a new class and implement something like this:

public IQueryable<ProductWithHasVariant> GetProduct(DBContext context, int productId)
{
  return from p in context.Products
         where p.ProductId == productId
         select new ProductWithHasVariant
         {
           p.ProductId,
           HasVariants = p.Variants.Any(),
           .
           .
           .
         };
}