How to query associations in Linq to Entity framework in .NET Ria Services

linq-to-entities, wcf-ria-services

Solution

Your GetItems looks fine to me. You could also do:

public IQueryable<Item> GetItems(int folderID)
{
    return this.Context.FolderItems
                       .Where(fi => fi.ID == folderID)
                       .Select(fi => fi.Items);
}

Both should return the same thing.

Problem

I have just started with Linq and Linq to Entity Framewok. On top of that with the .NET Ria services. My problem is that I have 2 tables Folder and Item with a many to many relationsship using a third "connection" table FolderItem like this: (source: InsomniacGeek.com) In the .NET RIA Service domain service, I want to create a method that returns all Items for a given FolderID. In T-SQL , that would something like this: ``` SELECT * FROM Item i INNER JOIN FolderItem fi ON fi.ItemID = i.ID WHERE fi.FolderID = 123 ``` My Linq knowledge is limited, but I want to do something like this: ``` public IQueryable<Item> GetItems(int folderID) { return this.Context.Items.Where(it => it.FolderItem.ID == folderID); } ``` This is not the correct syntax, it gives this error: Cannot convert lambda expression to type 'string' because it is not a delegate type What is the correct way of doing this (with associations) ? Can I user the .Include("FolderItem") somehow? Please, method syntax only. PS. Here's how it would look like using a Query Expression: ``` public IQueryable<Item> GetItemsByFolderID(int folderID) { return from it in this.Context.Items from fi in it.FolderItem where fi.Folder.ID == folderID select it; } ``` The qeustion is, how would it look like using the Method Based Query Syntax?

Original source