Wie kann ich Left Join in Linq verwenden, die wir in SQL verwenden?

Question

Wie kann ich Links Join in Linq verwenden, dass ich SQL-Abfrage schreibe?

select 
    p.Name, p.Family, 
    E.EmployTypecode, E.employtypeName, E.EmplytyppeTye 
from 
    personnel as p 
left join 
    Employee as E on E.EmployTypecode = p.EmployTypecode 

Answer 1

Verwenden Stichwort Join statt LEFT JOIN und es ist zwingend erforderlich "IN" Schlüsselwort und "DefaultIfEmpty()" Methode zu verwenden, als rechte Tabelle Nullwert zurückgibt.

var query = from p in personnel 
       join e in Employee on p.EmployTypecode equals e.EmployTypecode into t 
       from nt in t.DefaultIfEmpty() 
       orderby p.Name 

    select new 
    { 
     p.Name, p.Family, 
     EmployTypecode=(int?)nt.EmployTypecode, // To handle null value if Employtypecode is specified as not null in Employee table. 
     nt.employtypeName, nt.EmplytyppeTye 
    }.ToList(); 

Answer 2

es wie folgt tun:

var query = 
from p in personnel 
join e in Employee 
    on p.EmployTypecode equals e.EmployTypecode 
into temp 
from j in temp.DefaultIfEmpty() 
select new 
{ 
    name = p.name, 
    family = p.family, 
    EmployTypecode = String.IsNullOrEmpty(j.EmployTypecode) ? "" : j.EmployTypecode, 
    ...... 
} 

Answer 3

var q=(
       from pd in dataContext.personnel 
       join od in dataContext.Employee 
        on pd.EmployTypecode equals od.EmployTypecode 
        into t 
       from rt in t.DefaultIfEmpty() 
       orderby pd.EmployTypecode 
       select new 
       { 
        EmployTypecode=(int?)rt.EmployTypecode, 
        pd.Name, 
        pd.Family, 
        rt.EmplytyppeTye 
       } 
     ).ToList(); 

Answer 4

Warum nicht SQL-Abfrage verwenden EF LIST zu konvertieren. In EF 6.1

Schreib

public class personnel 
    { 
     public String Name { get; set; } 
     public String Family { get; set; } 
     public String EmployTypecode { get; set; } 
     public String employtypeName { get; set; } 
     public String EmplytyppeTye { get; set; } 
    } 

List<personnel> personnels = dbentities.Database.SqlQuery<personnel>(@"select 
    p.Name, p.Family, 
    E.EmployTypecode, E.employtypeName, E.EmplytyppeTye 
from 
    personnel as p 
left join 
    Employee as E on E.EmployTypecode = p.EmployTypecode ").ToList();