LINQ 查询删除包括在 where 子句中添加 `.Contains()` 时

Question

我有一个有点复杂的查询，我试图在 Linq（EntityFramework Core 2.1）中构建，我遇到了我无法理解的行为。 以下查询运行良好且看似高效：

var q = (
from n in TaskUpdates.Include(t => t.Status).Include("Task").Include("Task.Requirement").Include("User").Include("User.Employee")
where n.User.Employee.EmployeeNumber == 765448466
group n by n.UpdateDate into tu
select tu.OrderByDescending(t=>t.UpdateDate).FirstOrDefault()
)
.Select(x => x.Task.Requirement);

这可以按我的预期工作，执行我想要的所有连接，并在SELECT子句中包含预期的字段：

SELECT [t].[TaskUpdateID], [t].[Active], [t].[TaskId], [t].[Notes], [t].[StatusId], [t].[UpdateDate], [t].[UserId], [t.Task].[TaskID], [t.Task].[Active], [t.Task].[CreatedDate], [t.Task].[RequirementId], [t.Task].[UserId], [t.Task.Requirement].[RequirementID], [t.Task.Requirement].[Active], [t.Task.Requirement].[Description], [t.Task.Requirement].[Hours], [t.Task.Requirement].[Link], [t.Task.Requirement].[Name], [t.Task.Requirement].[RequirementTypeId], [t.Task.Requirement].[ExternalId], [t.Task.Requirement].[SortOrder], [t.Status].[StatusId], [t.Status].[Active], [t.Status].[IsComplete], [t.Status].[Title], [t.User].[UserId], [t.User].[Active], [t.User].[Created], [t.User].[EmployeeNumber], [t.User].[LastLogin], [t.User].[LastUpdated], [t.User.Employee].[EMPLOYEENUMBER], [t.User.Employee].[BEGINDATE], [t.User.Employee].[CITY], [t.User.Employee].[EMPLOYEETYPE], [t.User.Employee].[ENDDATE], [t.User.Employee].[FIRST_NAME], [t.User.Employee].[GENERATION_SUFFIX], [t.User.Employee].[STATUS], [t.User.Employee].[LAST_NAME], [t.User.Employee].[MIDDLE_NAME], [t.User.Employee].[MOBILE], [t.User.Employee].[ORGCODE], [t.User.Employee].[PHONE_NUMBER], [t.User.Employee].[PRIMARYEMAIL], [t.User.Employee].[STATE], [t.User.Employee].[STREET], [t.User.Employee].[TITLE], [t.User.Employee].[ZIPCODE], [t.User.Employee].[BUILDING], [t.User.Employee].[ROOM]
FROM [TaskUpdates] AS [t]
INNER JOIN [Tasks] AS [t.Task] ON [t].[TaskId] = [t.Task].[TaskID]
LEFT JOIN [Requirements] AS [t.Task.Requirement] ON [t.Task].[RequirementId] = [t.Task.Requirement].[RequirementID]
INNER JOIN [Status] AS [t.Status] ON [t].[StatusId] = [t.Status].[StatusId]
INNER JOIN [Users] AS [t.User] ON [t].[UserId] = [t.User].[UserId]
INNER JOIN [DirectoryPeople] AS [t.User.Employee] ON [t.User].[EmployeeNumber] = [t.User.Employee].[EMPLOYEENUMBER]
WHERE [t.User.Employee].[EMPLOYEENUMBER] = 765448466
ORDER BY [t].[UpdateDate]
GO

（我正在使用 LINQPad 来试验这个查询并获得 SQL。）特别是，结尾的.Select(...)方法正确地从查询中返回了Requirement object。

让我感到困惑的是，如果我想让这个查询返回多个员工的数据，并且我像这样更改where子句：

var employeeNumbers = new int[] { 765448466 };

var q = (
from n in TaskUpdates.Include(t => t.Status).Include("Task").Include("Task.Requirement").Include("User").Include("User.Employee")
//where n.User.Employee.EmployeeNumber == 765448466
where employeeNumbers.Contains(n.User.Employee.EmployeeNumber)
group n by n.UpdateDate into tu
select tu.OrderByDescending(t=>t.UpdateDate).FirstOrDefault()
)
.Select(x => x.Task.Requirement);

这完全按照我的预期更改了生成的 SQL WHERE子句，但它现在完全忽略了from子句中的Include ：

SELECT [t].[TaskUpdateID], [t].[Active], [t].[TaskId], [t].[Notes], [t].[StatusId], [t].[UpdateDate], [t].[UserId]
FROM [TaskUpdates] AS [t]
INNER JOIN [Users] AS [t.User] ON [t].[UserId] = [t.User].[UserId]
INNER JOIN [DirectoryPeople] AS [t.User.Employee] ON [t.User].[EmployeeNumber] = [t.User.Employee].[EMPLOYEENUMBER]
WHERE [t.User.Employee].[EMPLOYEENUMBER] IN (765448466)
ORDER BY [t].[UpdateDate]
GO

（仅在执行where时需要加入），最终.Select(...)的结果现在返回null 。

这是已知的行为，有或没有解释吗？ 我是否错误地使用了Include指令，或者是否有更好的方法/位置让他们使用 go 来解决这个问题？

Answer 1

我不能确定原因，我怀疑 EF 正在使用包含的不同翻译路径并且缺少包含，但是正如您所看到的，它根本没有翻译 GroupBy，所以它绝对可以重新设计以匹配更多的EF风格。

TaskUpdates
  .Include(x => x.Task)
      .ThenInclude(x => x.Requirement)
  .Where(x => employeeNumbers.Contains(x.User.Employee.EmployeeNumber))
  .ToList()
  .GroupBy(x => x.UpdateDate)
  .Select(x => new {
      UpdateDate = x.Key,
      FirstRequirement = x.First().Task.Requirement
  })
  .ToList();

This should translate the statements before the first ToList into SQL, populate the results in-memory and allow C# to do the groupby and aggregates on the whole object which SQL would be unable to do.