Whether I should write, simple join for common records? - asp.net-mvc

Question

I am developing an ASP.NET MVC application. I have two queries I want to get common records from those queries.
Am I suppose to write simple join to get the common records ?
var poList =
(from po in db.PurchaseOrders
where po.CompanyId == companyId &&
po.PartyId == partyId &&
(po.IsDeleted == false || po.IsDeleted == null)
select po into newPO
select new
{
Name = newPO.PONo,
Id = newPO.Id
});
var poList2 = (db.Employees.Where(x => x.Id == EmpID)
.SelectMany(x => x.Roles)
.SelectMany(x => x.Employees)
.Distinct()
.SelectMany(x => x.PurchaseOrders)
.Select(po => new { Name = po.PONo, Id = po.Id }));
I am trying to write the join but its asking for one more argument, how to write a simple join for common records ?
var finalPO = poList.Join(poList2).ToList();

Answer 1

You can use an overload of Join method to specify join conditions:
poList.Join(poList2, a => a.Name, b => b.Name, (a,b) => new { Name = b.PONo, Id = b.Id });

Answer 2

Union will give you all records from both:
http://msdn.microsoft.com/en-us/library/system.linq.enumerable.union.aspx
Join method will give you records that match on provided key, but requires more than just the two enumerables as parameters:
http://msdn.microsoft.com/en-us/library/bb534675.aspx

Answer 3

You don't need a join because you can apply the expressions in the first query to the "raw" result of the second one:
var poList2 = db.Employees.Where(x => x.Id == EmpID)
.SelectMany(x => x.Roles)
.SelectMany(x => x.Employees)
.Distinct()
.SelectMany(x => x.PurchaseOrders);
var result = from po in poList2
where po.CompanyId == companyId &&
po.PartyId == partyId &&
!po.IsDeleted
select po into newPO
select new
{
Name = newPO.PONo,
Id = newPO.Id
};
And if you need the result you originally intended to get from poList2:
var result2 = poList2.Select(po =>
{
Name = po.PONo,
Id = po.Id
};
So, generally speaking, you can do more with your query bodies if you postpone the projection to anonymous types.
Side note: I used !po.IsDeleted because I'd strongly recommend to make the field not nullable, with false as default value.