I am kind of lost between Join and GroupJoin. Which way is the right way to do INNER JOIN? On one hand Join is doing the right job, but I have to call Distinct. On the other hand GroupJoin is grouping by itself, but gives me empty RHS. Or there is a better way?
using System;
using System.Linq;
public class Foo
{
public string Name { get; set; }
public Foo(string name)
{
Name = name;
}
}
public class Bar
{
public Foo Foo { get; set; }
public string Name { get; set; }
public Bar(string name, Foo foo)
{
Foo = foo;
Name = name;
}
}
public class Program
{
public static Foo[] foos = new[] { new Foo("a"), new Foo("b"), new Foo("c"), new Foo("d") };
public static Bar[] bars = new[] { new Bar("1", foos[1]), new Bar("2", foos[1]) };
public static void Main(string[] args)
{
#if true
var res = foos.Join(
bars,
f => f,
b => b.Foo,
(f, b) => f
)
.Distinct();
#else
var res = foos.GroupJoin(
bars,
f => f,
b => b.Foo,
(f, b) => new { f, b }
)
.Where(t => t.b.Any())
.Select(t => t.f);
#endif
foreach (var r in res)
Console.WriteLine(r.Name);
}
}
Thanks!
The key to understanding this is to look at the types of the parameters for that last lambda you're passing in.
For Join
, the b
will be a single bar
, and you will get a row for every bar
that has a match.
While for GroupJoin
, the b
will be a collection of bar
, and you will get a single row for every foo
that has a match.
Both perform an inner join, but if you're looking for SQL's INNER JOIN
, the Join
method is what you want.
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