Question

I am trying to reproduce the following SQL query in Linq and need some help please.

select
   dbo.Documents.DocId, 
   dbo.Documents.ReykerAccountRef, 
   dbo.Documents.ReykerClientId DocClientID,
   CAAs.ClientId CAAClientIDCheck,
   ClientData.FullName ClientFullName, 
   CAAs.IFAId,  
   AdvisorData.FullName AdvisorFullName
from dbo.Documents
left join 
  dbo.CAAs on dbo.Documents.ReykerAccountRef = dbo.CAAs.AccountRef
left join 
  dbo.hmsProfileDatas AS ClientData
on 
  dbo.CAAs.ClientId = ClientData.ReykerClientID
left join 
  dbo.hmsProfileDatas AS AdvisorData
on 
  dbo.CAAs.IFAId = AdvisorData.ReykerClientID

I am trying to link to the same table twice, once for a client fullname and the other for an Advisor fullname.

The basic sql I want to produce in linq is

select table1.*,table2.*,a.Fullname, b.Fullname
from table1
left join
   table2 on table1.t2Id = table2.Id
left join
   table3 AS a 
on 
   table2.t3Id1 = table3.id1
left join
   table3 AS b 
on 
   table2.t3Id2 = table3.id2

So table one is joined to table2 and table2 has 2 foreign keys (t3Id1 and t3Id2) to table3 to different fields (id1 and id2).

This is what I have tried following some guidance, but it’s not returning anything! What’s going wrong?

        var results3 = from doc in DataContext.Documents
                       from caa
                           in DataContext.CAAs
                           .Where(c => c.AccountRef == doc.ReykerAccountRef)
                           .DefaultIfEmpty()
                       from cpd
                           in DataContext.hmsProfileDatas
                           .Where(pdc => pdc.ReykerClientID == caa.ClientId)
                           .DefaultIfEmpty()
                       from apd
                           in DataContext.hmsProfileDatas
                           .Where(pda => pda.ReykerClientID == caa.IFAId)
                           .DefaultIfEmpty()
                       select new DocumentInList()
                                  {
                                      DocId = doc.DocId,
                                      DocTitle = doc.DocTitle,
                                      ReykerDocumentRef = doc.ReykerDocumentRef,
                                      ReykerAccountRef = doc.ReykerAccountRef,
                                      ClientFullName = cpd.FullName,
                                      AdvisorFullName = apd.FullName,
                                      DocTypeId = doc.DocTypeId,
                                      DocTypes = doc.DocTypes,
                                      DocDate = doc.DocDate,
                                      BlobDocName = doc.BlobDocName,
                                      UploadDate = doc.UploadDate,
                                  };

Answer 1

I hope I understood your example correctly. Here’s another simple example, that should give what you need:

    private class User
    {
        public int UserId;
        public string Name;
        public int GroupId;
        public int CollectionId;
    }

    public class Group
    {
        public int GroupId;
        public string Name;
    }

    public class Collection
    {
        public int CollectionId;
        public string Name;
    }

    static void Main()
    {
        var groups = new[] { 
            new Group { GroupId = 1, Name = "Members" },
            new Group { GroupId = 2, Name = "Administrators" } 
        };
        var collections = new[] { 
            new Collection { CollectionId = 1, Name = "Teenagers" },
            new Collection { CollectionId = 2, Name = "Seniors" } 
        };
        var users = new[] { 
            new User { UserId = 1, Name = "Ivan", GroupId = 1, CollectionId = 1 },
            new User { UserId = 2, Name = "Peter", GroupId = 1, CollectionId = 2 },
            new User { UserId = 3, Name = "Stan", GroupId = 2, CollectionId = 1 },
            new User { UserId = 4, Name = "Dan", GroupId = 2, CollectionId = 2 },
            new User { UserId = 5, Name = "Vlad", GroupId = 5, CollectionId = 2 },
            new User { UserId = 6, Name = "Greg", GroupId = 2, CollectionId = 4 },
            new User { UserId = 6, Name = "Arni", GroupId = 3, CollectionId = 3 },
        };

        var results = from u in users
                      join g in groups on u.GroupId equals g.GroupId into ug
                      from g in ug.DefaultIfEmpty()
                      join c in collections on u.CollectionId equals c.CollectionId into uc
                      from c in uc.DefaultIfEmpty()
                      select new { 
                          UserName = u.Name, 
                          GroupName = g != null ? g.Name : "<No group>",
                          CollectionName = c != null ? c.Name : "<No collection>"
                      };
    }

It produces two join over one table to get data from other two tables.
Here’s the output:

Ivan    Members         Teenagers
Peter   Members         Seniors
Stan    Administrators  Teenagers
Dan     Administrators  Seniors
Vlad    <No group>      Seniors
Greg    Administrators  <No collection>
Arni    <No group>      <No collection>