left outer join in lambda/method syntax in Linq [duplicate]

Question

Possible Duplicate:
How do you perform a left outer join using linq extension methods

I can't find a left outer join example of Linq lambda (with extension methods), at least, not a clear one.

Let's say I have the following table:

Parent {     PID     // PK }  Child {     CID     // PK     PID     // FK     Text } 

I want to join Parent with Child, and for every child missing, I want the default value for Text to be "[[Empty]]". How can I do this with linq lambda syntax?

I currently have the following:

var source = lParent.GroupJoin(     lChild,     p => p.PID,     c => c.PID,     (p, g) =>         new // ParentChildJoined         {             PID = p.PID;             // How do I add child values here?         }); 

Answer 1

You're close. The following will select PID, CID and Text for each child, and PID, CID = -1 and Text = "[[Empty]]" for each parent with no children:

var source = lParent.GroupJoin(     lChild,     p => p.PID,     c => c.PID,     (p, g) => g         .Select(c => new { PID = p.PID, CID = c.CID, Text = c.Text })         .DefaultIfEmpty(new { PID = p.PID, CID = -1, Text = "[[Empty]]" }))     .SelectMany(g => g); 

Answer 2

from p in Parent join c in Child on p.PID equals c.PID into g from c in g.DefaultIfEmpty() select new  {    p.PID,    CID = c != null ? (int?)c.CID : null, // Could be null    Text = c != null ? c.Text : "[[Empty]]" } 

With lambda:

class ChildResult {    public int PID { get; set; }    public int? CID { get; set; }    public string Text { get; set; } }  lParent.SelectMany(p => p.Childs.Any() ?   p.Childs.Select(c => new ChildResult() { PID = c.PID, CID = c.CID, Text = c.Text }) :   new [] { new ChildResult() { PID = p.PID, CID = null, Text = "[[Empty]]" } } );