LINQ to SQL multiple tables left outer join

C#MysqlSqlLinqEntity Framework

C# Problem Overview


I have this query in SQL, and I want it to implement it in LINQ using Entity Framework, but how can I apply multiple tables left outer joins?

SELECT d.bookingid,
       d.labid,
       d.processid,
       p.prid,
       p.prno,
       d.DestinationBranchID,
       d.SendStatus
FROM   dc_tpatient_bookingd d
       LEFT OUTER JOIN dc_tpatient_bookingm m ON d.bookingid = m.bookingid
       LEFT OUTER JOIN dc_tpatient p ON p.prid = m.prid
       LEFT OUTER JOIN dc_tp_test t ON d.testid = t.testid
       LEFT OUTER JOIN dc_tp_groupm gm ON t.groupid = gm.groupid
       LEFT OUTER JOIN dc_tpanel pn ON m.panelid = pn.panelid
       LEFT OUTER JOIN dc_tp_organization og ON og.orgid = m.clientid
       LEFT OUTER JOIN dc_tp_ward w ON w.wardid = m.wardid
       LEFT OUTER JOIN dc_tp_branch tb ON tb.BranchID = m.BranchID
WHERE  d.processid = 6
       AND ( ( m.branchId = 1
               AND d.DestinationBranchID = 0 )
              OR ( d.DestinationBranchID = 1
                   AND d.sendstatus = 'R' ) )
       AND d.testid IN (SELECT testid
                        FROM   dc_tp_test
                        WHERE  subdepartmentid = 13)
       AND date_format(m.enteredon, '%Y/%m/%d') BETWEEN '2013/06/15' AND '2013/06/15'
GROUP  BY m.bookingid
ORDER  BY d.priority DESC,
       m.bookingid ASC

C# Solutions


Solution 1 - C#

Here is how left outer joins are implemented with LINQ. You should use GroupJoin (join...into syntax):

from d in context.dc_tpatient_bookingd
join bookingm in context.dc_tpatient_bookingm
     on d.bookingid equals bookingm.bookingid into bookingmGroup
from m in bookingmGroup.DefaultIfEmpty()
join patient in dc_tpatient
     on m.prid equals patient.prid into patientGroup
from p in patientGroup.DefaultIfEmpty()
// ... other joins here
where d.processid == 6 &&
      ((m.branchId == 1 && d.DestinationBranchID == 0) ||
       (d.DestinationBranchID == 1 && d.sendstatus == "R"))
// ... other conditions here
orderby d.priority descending, m.bookingid
select new {
   d.bookingid,
   d.labid,
   d.processid,
   p.prid,
   p.prno,
   m.bookingid // need for grouping
} into x
group x by x.bookingid into g
select g

This query joins three tables. You can join the rest of the tables the same way.

Solution 2 - C#

This is multiple left join sample with null checking (preventing null reference exception). Thnx to Nick!

void Main()
{
	var data = DataAccess.GetData();
	var res = 
		from m in data.Movies
		join ma in data.MovieActor on m.Id equals ma.MovieId into mma
		from ma in mma.DefaultIfEmpty()
		join p in data.People on (ma == null ? 0 : ma.ActorId) equals p.Id into pma
		from p in pma.DefaultIfEmpty()
		orderby m.Name
		select new {
			Movie = m.Name,
			Actor = p != null ? p.Name + " as " + ma.Name : ""
		};
	foreach (var el in res)
	{
		Console.WriteLine($"{el.Movie} - {el.Actor}");
	}
}

public class DataAccess
{
	public static Data GetData()
	{
		var list = new Data
		{
			Movies = new List<Movie>{
			 new Movie{ Id = 1, Name= "Raiders of the Lost Ark", Year = 1981},
			 new Movie{ Id = 2, Name= "Blade Runner", Year = 1982},
			 new Movie{ Id = 3, Name= "Star Wars: Episode IV - A New Hope", Year = 1977},
			 new Movie{ Id = 4, Name= "Total Recall", Year = 1990},
			 new Movie{ Id = 5, Name= "The Fugitive", Year = 1993},
			 new Movie{ Id = 6, Name= "Men in Black", Year = 1997},
			 new Movie{ Id = 7, Name= "U.S. Marshals", Year = 1998},
			 new Movie{ Id = 8, Name= "Batman", Year = 1989},
			 new Movie{ Id = 9, Name= "A Few Good Men", Year = 1992},
			 new Movie{ Id = 10, Name= "Tropic Thunder", Year = 2008},
			 new Movie{ Id = 11, Name= "Minority Report", Year = 2002},
			 new Movie{ Id = 12, Name= "The Fifth Element", Year = 1997},
			 new Movie{ Id = 13, Name= "District 9", Year = 2009},
			 new Movie{ Id = 14, Name= "12 Monkeys", Year = 1995},
			},
			People = new List<Person>{
		 		new Person{ Id = 1, Name = "Harrison Ford"},
		 		new Person{ Id = 2, Name = "Tommy Lee Jones"},
		 		new Person{ Id = 3, Name = "Will Smith"},
		 		new Person{ Id = 4, Name = "Michael Keaton"},
		 		new Person{ Id = 5, Name = "Will Smith"},
		 		new Person{ Id = 6, Name = "Jack Nicholson"},
		 		new Person{ Id = 7, Name = "Tom Cruise"}
		 	},
			MovieActor = new List<MovieActor>{
				new MovieActor{ MovieId = 1, ActorId = 1, Name = "Indy"},
				new MovieActor{ MovieId = 2, ActorId = 1, Name = "Rick Deckard"},
				new MovieActor{ MovieId = 3, ActorId = 1, Name = "Han Solo"},
				new MovieActor{ MovieId = 5, ActorId = 1, Name = "Dr. Richard Kimble"},
				new MovieActor{ MovieId = 5, ActorId = 2, Name = "Samuel Gerard"},
				new MovieActor{ MovieId = 6, ActorId = 2, Name = "Kay"},
				new MovieActor{ MovieId = 7, ActorId = 2, Name = "Samuel Gerard"},
				new MovieActor{ MovieId = 6, ActorId = 3, Name = "Jay"},
				new MovieActor{ MovieId = 8, ActorId = 4, Name = "Batman / Bruce Wayne"},
				new MovieActor{ MovieId = 8, ActorId = 6, Name = "Joker / Jack Napier"},
				new MovieActor{ MovieId = 9, ActorId = 6, Name = "Col. Nathan R. Jessep"},
				new MovieActor{ MovieId = 9, ActorId = 7, Name = "Lt. Daniel Kaffee"},
				new MovieActor{ MovieId = 10, ActorId = 7, Name = "Les Grossman"},
				new MovieActor{ MovieId = 11, ActorId = 7, Name = "Chief John Anderton"}
			}
			
		};
		return list;
	}
}

public class Data
{
	public List<Movie> Movies = new List<Movie>();
	public List<Person> People = new List<Person>();
	public List<MovieActor> MovieActor = new List<MovieActor>();
}

public class Person
{
	public int Id { get; set; }
	public string Name { get; set; }
}

public class Movie
{
	public int Id { get; set; }
	public string Name {get; set;}
	public int Year { get; set; }
}

public class MovieActor
{
	public int MovieId { get; set; }
	public int ActorId { get; set; }
	public string Name { get; set; } // appearance as
}

Attributions

All content for this solution is sourced from the original question on Stackoverflow.

The content on this page is licensed under the Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license.

Content TypeOriginal AuthorOriginal Content on Stackoverflow
QuestionEhsan SajjadView Question on Stackoverflow
Solution 1 - C#Sergey BerezovskiyView Answer on Stackoverflow
Solution 2 - C#Zoran BosnjakView Answer on Stackoverflow