SQL查询到LINQ表达式

本文关键字：表达式 LINQ 查询 SQL | 更新日期: 2023-09-27 18:04:52

无法将以下查询转换为LINQ表达式。你能帮我吗?

 SELECT Employee_Id_FK from TimeRegistrations as tr
  JOIN Employees em ON tr.Employee_Id_FK = em.id
  JOIN Managers m  ON em.Manager_Id_FK = m.id
  WHERE m.id = 4

这是我目前为止写的:

var result = from t in DB.TimeRegistrations
     join Employees  in DB.TimeRegistrations on t.Employee_Id_FK equals Employees.id
     join Managers in DB.Managers on .....          ;
// Display results.
foreach (var r in result)
{
Console.WriteLine(r);
}

SQL查询到LINQ表达式

如果您的数据库有外键:

 var result =from t1 in DB.TimeRegistrations
     join t2 in t1.Employees 
     join t3 in t2.Managers 
     where t3.id == "4"
     select t1

如果没有

 var result =from t1 in DB.TimeRegistrations
     join t2 in DB.Employees on t1.Employee_Id_FK equals t2.id
     join t3 in DB.Managers on t2.id equals t3.Manager_Id_FK 
     where t3.id == "4"
     select t1

然而更短的方式将是:

 var result = DB.Managers.Find(4).Employees.SelectMany(e=>e.TimeRegistrations)

或者不是直接的方式:

 var result = DB.TimeRegistrations
                .Where(t=>t.Employees.Any(e=>e.Managers.Any(m=>m.id == 4)))
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