LINQ method How to SelectMany with additional column from Parent class

Question

I have a class :

public class Parent
{
    public int ParentID { get; set; }
    public string ParentName { get; set; }
    public List<Child> Childs { get; set; }
}

public class Child
{
    public int ChildID { get; set; }
    public string ChildName { get; set; }
}

With Parent object, here's how I get all Childs value.

Parent obj = GetParent();
PrintExcel(obj.SelectMany(sm => sm.Childs);

But I also want to include ParentName value in the select command, how to achieve this?

With SQL query, I can do this

SELECT
    p.ParentName,
    c.ChildName
FROM
    Parent p
    INNER JOIN Child c ON
        p.ParentID = c.ParentID

Answer 1

Your LINQ example is flawed. Assuming you have a sequence of Parent (i.e. IEnumerable<Parent> or IQueryable<Parent>) called parents, you can access the parent inside the SelectMany at least in a two ways:

(A) Use Select inside the SelectMany:

parents.SelectMany(p => p.Childs.Select(c => new { p.ParentName, c.ChildName }))

(B) Use the SelectMany overload which allows you pass result selector:

parents.SelectMany(p => p.Childs, (p, c) => new { p.ParentName, c.ChildName })

And of course you can simply use the query syntax and let the compiler determine the correct method for you:

(from p in parents from c in p.Childs select new { p.ParentName, c.ChildName })