Как использовать .Count () в LINQ To SQL?

Question

Как я могу перевести этот запрос TSQL в LINQ To SQL?

Select p3.Alias, Count(p3.Alias) as [Count]  from Persons p1
INNER JOIN Addresses    a    ON  p1.Id       = a.Person
INNER JOIN Persons      p2   ON  a.CityX     = p2.Id
INNER JOIN ContrAgents  ca   ON  p2.Id       = ca.Slave
INNER JOIN Persons      p3   ON  ca.Master   = p3.Id
where p1.Type >9 and p1.Type<16 
group by  p3.Alias

Я хочу получить 2 вещи: data в p3.Alias ​​и data в p.Count().

List<cNumberOfObject> number = (from p1  in  vt.Persons 
                                            join a   in  vt.Addresses    on  p1.Id      equals  a.Person
                                            join p2  in  vt.Persons      on  a.CityX    equals  p2.Id
                                            join ca  in  vt.ContrAgents  on  p2.Id      equals  ca.Slave
                                            join p3  in  vt.Persons      on  ca.Master  equals  p3.Id
                                            where    p1.Type>9  &&  p1.Type<16
                                            group p3 by p3.Alias into p
                                            select new cNumberOfObject
                                            {
                                               // Subject = p3.Alias,
                                                Number  = p.Count()

                                            }).ToList();

Answer 1

Результатом group by является IGrouping . Вы можете получить доступ к значению столбца, сгруппировавшего ваши объекты, используя свойство Key в IGrouping:

var number = (from p1  in  vt.Persons 
              join a   in  vt.Addresses    on  p1.Id      equals  a.Person
              join p2  in  vt.Persons      on  a.CityX    equals  p2.Id
              join ca  in  vt.ContrAgents  on  p2.Id      equals  ca.Slave
              join p3  in  vt.Persons      on  ca.Master  equals  p3.Id
              where (p1.Type > 9 && p1.Type < 16)
              group p3 by p3.Alias into p
              select new cNumberOfObject
              {
                  Subject = p.Key, // The alias
                  Number  = p.Count()
              }).ToList()