Join two tabales and get all values in left table using WHERE condision for right table value using Linq lambda.

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I have two tables Entity and EntityPoints

Entity table

VB

EntityId | Name
   1     | E1
   2     | E2
   3     | E3

EntityPoints Table

VB

EntityId | QId |Points

1        | 1   |100
1        | 2   |200
2        | 2   |350

my expected output is:

VB

Name | EntityId |QId  | Points
E1   |   1      | 2   | 200
E2   |   2      | 2   | 350
E3   |   3      |null | null

my problem is using this two tables how to get all Names in Entity table using where condition for EntityPoints Table QId ...
I try with following code but it not contain all Names of Entity table.How can I do it ?

C#

using (var db = new EntityContext())
{
    var PGEpoint = db.EntityPoints 
        .Join(db.Entity , p => p.EntityId , q => q.EntityId , (p, q) => new { p, q })
        .Where(w => w.p.QId == 2)
        .Select(m => new TestModel
        {
            pointGEID = m.q.EntityId ,
            PointGE_name = m.q.Name,
            Points = m.p.Points

        }).ToList();
    return PGEpoint;
}

Posted 7-May-15 2:50am

sachika_88

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Richard Deeming · Accepted Answer · 2015-05-07T04:23:00

Something like this should work:

C#

using (var db = new EntityContext())
{
    return db.Entity.GroupJoin(
        db.EntityPoints.Where(p => p.QId == 2),
        entity => entity.EntityId,
        point => point.EntityId,
        (entity, points) => new 
        { 
            entity, 
            point = points.FirstOrDefault() 
        })
        .Select(m => new TestModel
        {
            pointGEID = m.entity.EntityId,
            PointGE_name = m.entity.Name,
            Points = (m.point == null) ? default(int?) : m.point.Points
        })
        .ToList();
}

Queryable.GroupJoin method (MSDN)[^]
How to: Perform Left Outer Joins (C# Programming Guide)[^]