LEFT OUTER JOIN in LINQ

Question

How to perform left outer join in C# LINQ to objects without using join-on-equals-into clauses? Is there any way to do that with where clause? Corr

Answer 1

Simple solution for the LEFT OUTER JOIN:

var setA = context.SetA;
var setB = context.SetB.Select(st=>st.Id).Distinct().ToList();
var leftOuter  = setA.Where(stA=> !setB.Contains(stA.Id)); 

notes:

• To improve performance SetB could be converted to a Dictionary (if that is done then you have to change this: !setB.Contains(stA.Id)) or a HashSet
• When there is more than one field involved this could be achieve using Set operations and a class that implement: IEqualityComparer