Linq-to-SQL：如何对子选择执行计数

Question

我仍在设法弄清楚如何正确使用LINQ-to-SQL，而不仅仅是编写自己的存储过程。

在代码中，将一个userId传递到该方法中，然后LINQ使用它从与该userId匹配的GroupTable表中获取所有行。 GroupUser表的主键是GroupUserId ，它是Group表中的外键。

    /// <summary>
    /// Return summary details about the groups a user belongs to
    /// </summary>
    /// <param name="userId"></param>
    /// <returns></returns>
    public List<Group> GroupsForUser(int userId)
    {
        DataAccess.KINv2DataContext db = new DataAccess.KINv2DataContext();
        List<Group> groups = new List<Group>();

        groups = (from g in db.Groups
                  join gu in db.GroupUsers on g.GroupId equals gu.GroupId
                  where g.Active == true && gu.UserId == userId
                  select new Group
                  {
                      Name = g.Name,
                      CreatedOn = g.CreatedOn
                  }).ToList<Group>();


        return groups;
    }
}

这可以正常工作，但是我还想返回组中用户的总数以及该组所有权下的联系人总数。

伪代码嗨！

    /// <summary>
    /// Return summary details about the groups a user belongs to
    /// </summary>
    /// <param name="userId"></param>
    /// <returns></returns>
    public List<Group> GroupsForUser(int userId)
    {
        DataAccess.KINv2DataContext db = new DataAccess.KINv2DataContext();
        List<Group> groups = new List<Group>();

        groups = (from g in db.Groups
                  join gu in db.GroupUsers on g.GroupId equals gu.GroupId
                  where g.Active == true && gu.UserId == userId
                  select new Group
                  {
                      Name = g.Name,
                      CreatedOn = g.CreatedOn,
                      // ### This is the SQL I would write to get the data I want ###
                      MemberCount = ( SELECT COUNT(*) FROM GroupUser AS GU WHERE GU.GroupId = g.GroupId ),
                      ContactCount = ( SELECT COUNT(*) FROM Contact AS C WHERE C.OwnerGroupId = g.GroupId )
                     // ### End of extra code ###
                  }).ToList<Group>();


        return groups;
    }
}

Answer 1

我在SQL中写的LINQ版本似乎可以解决问题，但我认为这行不通！

    /// <summary>
    /// Return summary details about the groups a user belongs to
    /// </summary>
    /// <param name="userId"></param>
    /// <returns></returns>
    public static List<Group> GroupsForUser(int userId)
    {
        DataAccess.KINv2DataContext db = new DataAccess.KINv2DataContext();
        List<Group> groups = new List<Group>();

        groups = (from g in db.Groups
                  join gu in db.GroupUsers on g.GroupId equals gu.GroupId
                  where g.Active == true && gu.UserId == userId
                  select new Group
                  {
                      GroupId = g.GroupId,
                      Name = g.Name,
                      CreatedOn = g.CreatedOn,
                      ContactCount = (from c in db.Contacts where c.OwnerGroupId == g.GroupId select c).Count(),
                      MemberCount = (from guu in db.GroupUsers where guu.GroupId == g.GroupId 
                                     join u in db.Users on guu.UserId equals u.UserId
                                     where u.Active == true 
                                     select gu ).Count()
                  }).ToList<Group>();

        return groups;
    }