使用常规版本的 EF 6.x,我可以使用以下查询非常轻松地执行子查询:
var q = from u in db.User
let actions = from ua in db.UserActions
where ua.UserId == u.Id && ua.Approved
select ua
where u.Active
select new { User = u, Actions = actions.ToList() }
var result = await q.ToListAsync()
当我尝试在我的 ASP.NET Core 2.0 EntityFramework 驱动的应用程序中执行相同的代码时,我的应用程序只是卡住并且永远不会返回结果。
我尝试了一些变体,但一旦子查询作为初始查询的一部分执行后,所有变体都会挂起:
- 子查询(与上面相同,有一些变化)
- 左外连接
另一个子查询变体(也卡在执行上):
var q = from u in db.User
let actions = (from ua in db.UserActions
where ua.UserId == u.Id && ua.Approved
select ua).ToList()
where u.Active
select new { User = u, Actions = actions }
另一个子查询变体(也卡在执行上):
var q = from u in db.User
let actions = db.UserActions.Where(ua => ua.UserId == u.Id && ua.Approved)
where u.Active
select new { User = u, Actions = actions.ToList() }
左外连接的另一种变体(执行时也会挂起):
var forUserId = "test";
var q = from u in db.User
join ua in db.UserActions on u.Id equals ua.UserId into actions
from ua in action.DefaultIfEmpty()
where u.Active
select new { User = u, Actions = ua}
下面的代码有效,但很明显,子查询的执行被推迟了,一旦我们尝试访问 Action
属性,它就会启动另一个查询:
var q = from u in db.User
let actions = from ua in db.UserActions
where ua.UserId == u.Id && ua.Approved
select ua
where u.Active
select new { User = u, Actions = actions }
var result = await q.ToListAsync()
foreach (var r in result)
{
foreach(var a in r.Actions)
{
// extra database requests is executed for each result row
// .. process action.
}
}
如何执行子查询并获取实体列表,其中每个实体分配子实体列表,使用子查询接收?
最佳答案
我不确定。但是,您可以尝试“.ToList()”。
var q = (from u in db.User
join ua in db.UserActions on u.Id equals ua.UserId into actions
from ua in action.DefaultIfEmpty()
where u.Active
select new {u,ua}).ToList();
关于c# - Entity Framework .NET Core 2.0 查询在执行子查询时挂起,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45805182/