Left outer join in LINQ query

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LEFT OUTER JOIN in LINQ

How to make LINQ query with left outer joins?

Just type *c# linq left outer join* in google and get at least [How to: Perform Left Outer Joins (C# Programming Guide)](http://msdn.microsoft.com/en-us/library/vstudio/bb397895.aspx) — horgh, Jan 29 '13 at 05:29
@KonstantinVasilcov Now, now, Konsty - be nice to new commers. You should give him an appropriate link [like this one](http://bit.ly/WuihEC). Don't you agree? — Konrad Viltersten, Jan 29 '13 at 07:29
@KonradViltersten 81 of reputation is fair enough to be already aware of the rules of this site. I guess I had given him all I was expected to. — horgh, Jan 29 '13 at 07:41
@KonstantinVasilcov I suspect you missed my point. Click the link and see what I meant. :) — Konrad Viltersten, Jan 29 '13 at 08:03
Related post - [Linq join iquery, how to use defaultifempty](https://stackoverflow.com/q/19293844/465053) — RBT, Mar 07 '19 at 05:26

score 10 · Accepted Answer · answered Jan 29 '13 at 05:23

You can use Enumerable.DefaultIfEmpty Method for left outer join.

You may see: How to: Perform Left Outer Joins (C# Programming Guide) - MSDN

Consider the following example from MSDN,

class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

class Pet
{
    public string Name { get; set; }
    public Person Owner { get; set; }
}

Left outer join query can be:

var query = from person in people
            join pet in pets on person equals pet.Owner into gj
            from subpet in gj.DefaultIfEmpty()
            select new { person.FirstName, PetName = (subpet == null ? String.Empty : subpet.Name) };

score 4 · Answer 2 · answered Jan 29 '13 at 05:25

4

 var query = (from t1 in Context.Table1
              join t2temp in Context.Table2 on t1.Id equals t2.Id into tempJoin
              from t2 in tempJoin.DefaultIfEmpty()
              select ...);

answered Jan 29 '13 at 05:25

Felix

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Left outer join in LINQ query

2 Answers2