实体框架4.3，使用联接

Question

I am having some issues doing joins in EF using my service layer. Whenever I try to do a join I get the following error:

" "

I have spent countless hours trying to figure this out. Most of the articles I have seen deal with joining entity sets from different contexts. However this is happening to me using the same DB. What am I doing wrong?

Example code:

 public virtual IList<ProductVariantAttribute> GetProductVariantAttributes(int ProductID)
     {
         var query = from pva in _productVariantAttributeRepository.Table
                     join b in _productAttributeRepository.Table on pva.ProductAttributeID equals b.ProductAttributeID
                     where pva.ProductID == ProductID
                     select pva;

         var productVariantAttributes = query.ToList();
        return productVariantAttributes;
    }

Answer 1

This has nothing to do with databases. It has everything to do with instances of ObjectContext .

You are referencing two different repositories in your query. I guess each of them is wrapping an EntityContext. This will cause this message.

It is also an anti-pattern. I recommend that you open exactly one EntityContext per HTTP-request or per WCF call or whatever your unit of work is.