LINQ JOIN和OUTER JOIN-如何将SQL转换为LINQ表达式
本文关键字:LINQ SQL 转换 表达式 JOIN OUTER JOIN- | 更新日期: 2023-09-27 18:25:04
我想将以下SQL查询转换为LINQ表达式(使用Entity Framework 6.1)。到目前为止,我还找不到一个可接受的LINQ表达式来产生类似的结果。如果您能将这个简单的SQL语句转换为LINQ express,我们将不胜感激。
SELECT AAG.Id AS GroupId,
A.Id AS ActivityId,
A.Title As Title,
CASE WHEN AA.CompletedOn IS NULL THEN CAST(1 AS bit) ELSE CAST(0 AS bit) END AS Completed,
COALESCE(AAG.PointValue, 0) + SUM(COALESCE(AQ.PointValue, 0)) AS PointTotal
FROM ActivityAssignmentGroup AAG
INNER JOIN ActivityAssignment AA ON AA.GroupId = AAG.Id
INNER JOIN Activity A ON AA.ActivityId = A.Id
LEFT OUTER JOIN ActivityQuestion AQ ON AQ.ActivityId = A.Id
WHERE AAG.AssignedToId = 6
GROUP BY AAG.Id, A.Id, A.Title, CASE WHEN AA.CompletedOn IS NULL THEN CAST(1 AS bit) ELSE CAST(0 AS bit) END, COALESCE(AAG.PointValue,0)
如果没有LEFT OUTER JOIN部分,下面的LINQ语句将部分完成,但我无法找到添加LEFT OUTER JOIN条件的适当语法:
var assignments = await (from g in db.AssignmentGroups.AsNoTracking().Where(x => x.AssignedToId == studentTask.Result.PersonId)
join aa in db.ActivityAssignments.AsNoTracking() on g.Id equals aa.GroupId
join a in db.Activities.AsNoTracking() on aa.ActivityId equals a.Id
select new ActivityListViewModel
{
Id = a.Id,
Points = g.PointValue ?? 0,
Title = a.Title,
GroupId = g.Id,
Complete = (aa.CompletedOn != null)
});
编辑:
谢谢你的回复,鲍勃。我尝试使用DefaultIfEmpty并查看实体框架生成的SQL查询结果,但没有成功。在发表这篇文章之前,这是我尝试的LINQ声明:
var assignments = from g in db.AssignmentGroups.AsNoTracking().Where(x => x.AssignedToId == studentTask.Result.PersonId)
join aa in db.ActivityAssignments.AsNoTracking() on g.Id equals aa.GroupId
join a in db.Activities.AsNoTracking() on aa.ActivityId equals a.Id
from aq in db.ActivityQuestions.Where(q => q.ActivityId == a.Id).DefaultIfEmpty()
group aq by new { ActivityId = aq.ActivityId, Title = a.Title, GroupId = g.Id, Points = g.PointValue ?? 0, Completed = (aa.CompletedOn != null) } into s
select new ActivityListViewModel
{
Id = s.Key.ActivityId,
Points = s.Key.Points + s.Sum(y => y.PointValue ?? 0), //g.PointValue ?? 0,
Title = s.Key.Title,
GroupId = s.Key.GroupId,
Complete = s.Key.Completed
};
当然,它也不起作用。结果是缺少Id(ActivityId)的项目。
您需要DefaultIfEmpty()将联接转换为左外部联接,MSDN中的文档到此
var assignments = await (from g in db.AssignmentGroups.AsNoTracking().Where(x => x.AssignedToId == studentTask.Result.PersonId)
join aa in db.ActivityAssignments.AsNoTracking() on g.Id equals aa.GroupId
join a1 in db.Activities.AsNoTracking() on aa.ActivityId equals a1.Id into a2
from a in a2.DefaultIfEmpty()
select new ActivityListViewModel
{
Id = a == null ? null : a.Id,
Points = g.PointValue ?? 0,
Title = a == null ? null : a.Title,
GroupId = g.Id,
Complete = (aa.CompletedOn != null)
});
只是为了结束循环(感谢Bob Vale)。。。下面的查询有效:
var assignments = from g in db.AssignmentGroups.AsNoTracking().Where(x => x.AssignedToId == studentTask.Result.PersonId)
join aa in db.ActivityAssignments.AsNoTracking() on g.Id equals aa.GroupId
join a in db.Activities.AsNoTracking() on aa.ActivityId equals a.Id
from aq in db.ActivityQuestions.Where(q => q.ActivityId == a.Id).DefaultIfEmpty()
group aq by new { ActivityId = a.Id, Title = a.Title, GroupId = g.Id, Points = g.PointValue ?? 0, Completed = (aa.CompletedOn != null) } into s
select new ActivityListViewModel
{
Id = s.Key.ActivityId,
Points = s.Key.Points + s.Sum(y => y.PointValue ?? 0), //g.PointValue ?? 0,
Title = s.Key.Title,
GroupId = s.Key.GroupId,
Complete = s.Key.Completed
};
问题是按条件分组,在我本应使用a.Id的情况下使用ag.ActivityId。