Question

我们正在将实体框架纳入我的应用程序中。我已经将很多简单的存储过程转换为linq查询但是这个给我带来麻烦，我不确定我哪里出错了。我的大脑变成了果冻，我无法使它发挥作用。我将非常感谢您的帮助，请耐心等待。

我的SQL是：

SELECT ...
FROM tblProjectAssignment 
INNER JOIN tblProjectAssignmentCollection 
   ON tblProjectAssignment.AssignmentID = tblProjectAssignmentCollection.AssignmentID 
RIGHT OUTER JOIN tblCEQRPhaseIIUsers 
   ON tblProjectAssignment.UserID = tblCEQRPhaseIIUsers.UserID 
LEFT OUTER JOIN tblCEQRAccessUserRole 
   ON tblCEQRPhaseIIUsers.UserRoleTypeID = tblCEQRAccessUserRole.UserRoleTypeID

我需要帮助将上面的内容转换为linq查询。我知道DefaultIfEmpty()用于外连接，但是我运行查询时得到的结果不正确。所以，我需要的是tblCEQRPhaseIIUsers以使所有结果与其他表中的相应结果无关。以下查询的行为与所有表都具有内部联接一样。

var query = from PATable in db.tblProjectAssignments
            from PACTable in db.tblProjectAssignmentCollections.Where(la => la.AssignmentID == PATable.AssignmentID)
            from UserTable in db.tblCEQRPhaseIIUsers.Where(la => la.UserID == PATable.UserID).DefaultIfEmpty()
            from UserRoleTable in db.tblCEQRAccessUserRoles.Where(la => la.UserRoleTypeID == UserTable.UserRoleTypeID).DefaultIfEmpty()
            where (UserTable.FirstName.ToLower().Contains(search.FirstName.Trim().ToLower()) || search.FirstName == null)
            where (UserTable.LastName.ToLower().Contains(search.LastName.Trim().ToLower()) || search.LastName == null)
            where (PACTable.CEQRNumber.ToLower().Contains(search.CEQRNumber.Trim().ToLower()) || search.CEQRNumber == null)
            where (PACTable.ProjectName.ToLower().Contains(search.ProjectName.Trim().ToLower()) || search.ProjectName == null)
            where (PATable.IsActive == true)
            where (UserTable.IsActive == true)
            select new
            {
                AssignmentID = PATable.AssignmentID,
                UserID = PATable.UserID,
                FirstName = UserTable.FirstName,
                MiddleName = UserTable.MiddleName ?? string.Empty,
                LastName = UserTable.LastName,
                UserRole = UserRoleTable.UserRoleName,
                CEQRNumber = PACTable.CEQRNumber,
                ProjectName = PACTable.ProjectName,
                CollectionID = PACTable.CollectionID,
                EmailAddress = UserTable.EmailAddress,
                AssignmentIsActive = PACTable.IsActive
            };

Answer 1

问题是您无法在right joins中linq执行此操作。好消息是您可以重写查询以避免使用right join。您可以通过重新排列表格并使用left joins来实现此目的。

目前你正在这样做：

select ...
from [MainTable] m
inner join [InnerTable] i on m.Num = i.Num
right join [RightTable] r on m.Num = r.Num
left join [LeftTable] l on r.Num = l.Num

这应该等同于：

select... 
from [RightTable] r 
left join [LeftTable] l on r.Num = l.Num
left join [MainTable] m on m.Num = r.Num
left join [InnerTable] i on m.Num = i.Num

现在您的查询没有right joins，您应该可以编写linq查询

linq左右连接

1 个答案: