LINQ: How to do JOIN using the linq extension method style on multiple fields?

Question

In the Join below, I'd like to use multiple fields to do the join rather than just one field.

var join = group.Join(procSums, g => g.DeptID, ps => ps.key.deptID, (g, ps)...

All examples Ive found use the query style to do this and I can't translate it.

Thanks!

Answer 1

You just have to Join based on new anonymous objects:

// ClasID is a placeholder, it could be any property you'd like
var join = group.Join(procSums,
                      g => new { g.DeptID, g.UnitLoc, g.Proc },
                      ps => new 
                            { 
                              DeptID = ps.key.deptID, 
                              UnitLoc = ps.key.unitLoc,
                              Proc = ps.key.procName 
                            },
                      (g, ps) => new { g, ps });

Answer 2

You need to pass lambda expressions that create anonymous types with the fields.
For example:

group.Join(procSums, g => new { g.DeptID, g.OtherField }, ps => new { ps.key.deptID, ps.key.OtherField }, ...)

The anonymous types must match exactly.