How to join one row to every row in source table using LINQ

Question

I have the following table (table A):

ID | Data  |
1  | Data1 |
2  | Data2 |
3  | Data3 |
4  | Data4 |

I have table B that has 1 row :

DummyID | Dummy  |
1       | Dummy1 |

I have to join table A with table B in the following way:

ID | Data  |DummyID | Dummy  |
1  | Data1 |1       | Dummy1 |
2  | Data2 |1       | Dummy1 |
3  | Data3 |1       | Dummy1 |
4  | Data4 |1       | Dummy1 |

Obviously I can't use any ID in the on clause.

from item in context.TableA
join dummy in context.TableB on ? = ?
select new 
 {
  RowA=item,
  Dummy=dummy
 }

How could I do that with LINQ?

Answer 1

That's a cross join which you can get via Linq in the following way

from item in context.TableA
from dummy in context.TableB
select new 
 {
  RowA=item,
  Dummy=dummy
 }

Or the following in method syntax

context.TableA.SelectMany(
    item => context.TableB.Select(dummy => new { RowA = item, Dummy = dummy }));

Note that if TableB every has more than one row you'll end up with N times M rows where N is the number of rows in TableA and M is the number of rows in TableB.

Answer 2

No need to join at all.

from item in context.TableA
select new 
{
    RowA = item,
    Dummy = context.TableB.FirstOrDefault()
}

Having said that, I'd have to question why you're doing this. The idea of LINQ is to get your relational data into an object-oriented form. Why not just retrieve the TableB information once and do whatever processing you need to do in-memory? It would reduce the size of the payload you're transferring from the database back to the application.

Answer 3

Why do you want to use join. You want to use each item in your old sequence to create a different item in your new sequence. In LINQ you would use Enumerable.Select for this:

var dummy = context.Dummy.FirstOrDefault();
var newSequence = context.TableA
    .Select(itemInTableA =>
        new
        {
            RowA = itemInTableA,
            Dummy = dummy,
        });