JOIN by LINQ in C#

Question

I need to make a Join by LINQ in two lists using codeList. List 1 must exist in the second list (list 2) and must be returned. How do I do that? Obs.: I never Join via LINQ in c#

Answer 1

you can do it this way.:

OUTER JOIN

var set1 = new HashSet<Entity1>();
var set2 = new HashSet<Entity2>();

var query =
    from entity1 in set1
    join entity2 in set2 on entity1.Codigo equals entity2.Codigo
    select new {
        Entity1 = entity1,
        Entity2 = entity2
    };

LEFT JOIN

var set1 = new HashSet<Entity1>();
var set2 = new HashSet<Entity2>();

var query =
    from entity1 in set1
    join entity2 in set2 on entity1.Codigo equals entity2.Codigo into lSet
    from entity2 in lSet.DefaultIfEmpty()
    select new {
        Entity1 = entity1,
        Entity2 = entity2
    };

Remembering that it is not possible to make a Right Join, at most you can make a Left Join reversing the order of collections.

RIGHT JOIN

var set1 = new HashSet<Entity1>();
var set2 = new HashSet<Entity2>();

var query =
    from entity2 in set2
    join entity1 in set1 on entity2.Codigo equals entity1.Codigo into rSet
    from entity1 in rSet.DefaultIfEmpty()
    select new {
        Entity1 = entity1,
        Entity2 = entity2
    };

Nor is it possible to do the Full Join in a simple way, you will have to make a Left Join and a "Right Join", then unite both.

FULL JOIN

var set1 = new HashSet<Entity1>();
var set2 = new HashSet<Entity2>();

var lQuery =
    from entity1 in set1
    join entity2 in set2 on entity1.Codigo equals entity2.Codigo into lSet
    from entity2 in lSet.DefaultIfEmpty()
    select new {
        Entity1 = entity1,
        Entity2 = entity2
    };

var rQuery =
    from entity2 in set2
    join entity1 in set1 on entity2.Codigo equals entity1.Codigo into rSet
    from entity1 in rSet.DefaultIfEmpty()
    select new {
        Entity1 = entity1,
        Entity2 = entity2
    };

var query = lQuery.Union(rQuery);