pita pita - 17 days ago 9
ASP.NET (C#) Question

Multiple tables left join using Linq

I know the Linq's left join is similar like this:

var q=from e in db.Employes   
join o in db.Orders on e equals o.Emoloyee into ords  
from on in ords.DefautIfEmpty()
select new
{      
e.FirstName,     
e.LastName   
  };


then how about the multiple join? here is my code

var personalInfoQuery = from t in crnnsupContext.Tombstones
join p in crnnsupContext.ProvStates on t.ProvinceState equals p.ProvinceStateID
join n in crnnsupContext.NursingSchools on t.NursingSchool equals n.SchoolID
join i in crnnsupContext.InitialEducations on t.InitialEducation equals SqlFunctions.StringConvert((double)i.InitalEducationID, 1)
join g in crnnsupContext.tbl_GraduatedProvCountry on t.GradPovCountry equals g.id
where t.RegNumber == _username
select new CPersonalInfo
{
ProvState = p,
Tombstone = t,
NursingSchool = n,
InitialEducation = i,
GraduatedProvCountry = g,
};


each joined table could have "null" field. can any help me, thanks

Answer Source

Multi join should look quite similar - it gets quite verbose, but I would give this a try. You might need some null checking in the final where line too.

var personalInfoQuery = from t in crnnsupContext.Tombstones
                        join p in crnnsupContext.ProvStates on t.ProvinceState equals p.ProvinceStateID into group1
                        from g1 ini group1.DefaultIfEmpty()
                        join n in crnnsupContext.NursingSchools on g1.NursingSchool equals n.SchoolID into group2
                        from g2 in group2.DefaultIfEmpty()
                        join i in crnnsupContext.InitialEducations on g2.InitialEducation equals SqlFunctions.StringConvert((double)i.InitalEducationID, 1) into group3
                        from g3 in group3.DefaultIfEmpty()
                        join g in crnnsupContext.tbl_GraduatedProvCountry on g3.GradPovCountry equals g.id into group4
                        from g4 in group4.DefaultIfEmpty()
                        where g4 == null || g4.RegNumber == _username
                        select new CPersonalInfo
                        {
                            ProvState = p,
                            Tombstone = t,
                            NursingSchool = n,
                            InitialEducation = i,
                            GraduatedProvCountry = g,
                         };

There seems to be another way of doing outer joins as well but without having something to test it on I'm not even sure if it's possible to use it in this case - check out the answer on this post if you're interested: outer join in linq