LINQ 查询从由三个表连接的表中获取数据

Question

I have three tables.

1. organisationalUnit
2. user
3. Tasks

I want to return back data from the tasks table where the authorized user is in a particular department and the user too is in this department. For example, Sally is in the HR department. She wants to view Jim's tasks. Jim is also in the HR department with sally, therefore she is allowed to view his tasks. However, she should not be able to view John's tasks as he is in the sales department.

organisationalUnit
--------------------
ID     |     name
--------------------
1      |     HR
2      |     Sales




      Users
----------------------------------------
ID     |     name     |  OUID(FK)
----------------------------------------
4      |     Jim      |  1
5      |     Sally    |  1
6      |     John     |  2



      Tasks
----------------------------------------------
ID     |     TaskInfo           |  userID(FK)
-----------------------------------------------
1      |     Task for Jim       |     4
2      |     Task for john      |     5
3      |     Task for Sally     |     6

current LINQ code

public async Task<IEnumerable<TaskSchedule>> GetTasks(string RoleName)
{         
     // return back ou ID
     var OUObjReturned = _context.OrganisationalUnits.Where(o => o.Name == RoleName).ToList();
     var OUID = OUObjReturned[0].Id;

     // get users based on the OUID       
     var userObjects = _context.Users.Where(u => u.OUId == OUID).ToList();

     // returns back with an array of users that have the Organisational unit ID   
     var userIDFromObject = userObjects[0].Id;

     //need further code to query the task table to return back tasks based on userID


}

I am now stuck on what to do after I get back the list of users with their ids. Is there a better way to code up the LINQ query than the one I have done above?

The LING query should be able to return back a list of tasks based on the organisationalUnit ID being sent into the query first. In the case above, sending the organisationalUnit ID of 1, should return back task row 1 and 2 as jim and sally are in OUID 1.

Answer 1

Try the below linq:

var roleName = "HR";
var tasks = (from t in _context.Tasks
            join u in _context.Users on t.UserId equals u.Id
            join o in _context.OrganisationalUnits on u.OUID equals o.Id
            where o.Name == RoleName
            select t).ToList();

Below is the Test:

public class OrganisationalUnit
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
    [ForeignKey("OrganisationalUnit")]
    public int OUID { get; set; }
}

public class Task
{
    public int Id { get; set; }
    public string TaskInfo { get; set; }
    [ForeignKey("User")]
    public int UserId { get; set; }
}

Result:

Answer 2

public async Task<IEnumerable<TaskSchedule>> GetTasks(string RoleName)
{
   // Here you found the OU
   var OUObjReturned = await _context.OrganisationalUnits
    .Where(o => o.Name == RoleName)
    .FirstOrDefault();

   // Now get list of users id
   var userObjects = await _context.Users
    .Where(u => u.OUId == OUObjReturned.ID)
    .Select(u => u.ID)
    .ToListAsync();

   // Return Tasks
   return await _context.Tasks
    .Where(t => userObjects.Contains(t.UserID)
    .ToListAsync();

}

But there is other way: (Assuming that the FK are well configured) and the models included navigation properties Ex: User must include reference to organisationalUnit:

public class User
   {
      public int ID {get; set;}
      public string Name {get; set;}
      public OrganizationalUnit OU {get; set;}
      public int OUID {get; set;}
   }

Now you can query directly using the navigation properties see EF Net Core Relationships

public async Task<IEnumerable<TaskSchedule>> GetTasks(string RoleName)
{
   // Return Tasks
   return await _context.Tasks
    .Include(t => t.User)
    .Where(t => User.OU.Name == RoleName)
    .ToListAsync();
}