Question

I have two tables that are not related using a foreign key but should be joinable. The relation (not FK) is one-to-many. Example:

Parent <- 1-to-many -> Child

1. I would like to query parents while joining children, even if they don’t have children (left join?).
2. I would like to select a parent while manually setting the children property through some action

Sample:

    using(var context = new Test.Models.Ef.Entities())
    {
        var products = from p in context.Parent
                join c in context.Child on p.key equals c.parentkey
                select new {Parent = p, Child = c};
    } 

Questions:

1. How do I “left join” the context.Child table in the above example?
2. How do I “group” the children by parent, while manually selecting it’s children in a property?
   • Pseudo: select p => p.Children = select c group by p

Answer 1

var products = from p in context.Parent
            join c in context.Child on p.key equals c.parentkey
            into pc select new { p, pc }

This executes a GroupJoin, which translates to an outer join.