9.1: Follow a User in API

Update UserService

We'll just add one method to for this, so we'll add it to the UserService. Alternatively, you could create a new FollowService if you forsee the application expanding after you finish the tutorial. For now, we'll keep them together for simplicity's sake.

In IUserService.cs, add a new method signature called GetFollow. Again, the wording here is a bit awkward - but, think of this as a 'follow event' - a case of one user following another.

Task<Follow> GetFollow(int userId, int recipientId);

Implement the method in UserService.cs:

public async Task<Follow> GetFollow(int userId, int recipientId)
{
    return await _context
                    .Follows
                    .FirstOrDefaultAsync(u => u.FollowerId == userId &&
                                              u.FolloweeId == recipientId);
}

We'll use this method to check if a User has already followed a particular User.

Update UsersController

Next, we'll add a new POST method to UsersController.cs:

[HttpPost("{id}/follow/{recipientId}")]
public async Task<IActionResult> FollowUser(int id, int recipientId)
{
    if (id != int.Parse(User.FindFirst(ClaimTypes.NameIdentifier).Value))               //  1.
        return Unauthorized();

    var follow = await _userService.GetFollow(id, recipientId);                         //  2.

    if (follow != null)                                                                 //  3.
        return BadRequest("You already followed this user.");

    if (await _userService.GetUser(recipientId) == null)                                //  4.
        return NotFound();

    follow = new Follow                                                                 //  5.
    {
        FollowerId = id,
        FolloweeId = recipientId
    };

    _userService.Add<Follow>(follow);                                                   //  6.

    if (await _userService.SaveAll())                                                   //  7.
        return Ok();

    return BadRequest("Failed to add user.");                                           //  8.
}

1. Check whether the token has rights to access this endpoint.

2. Gets the 'follow event` from the database

3. Checks if it isn't null - if it is, it returns a BadRequest()

4. Checks whether the user with the given recipientId exists - if it doesn't, return NotFound()

5. Create a new Follow entity

6. Add the new Follow entity - using the generic Add() method we created earlier

7. Tries to save changes to the database. If successful, it returns Ok()

8. If unsuccessful, it returns a BadRequest()

Test in Postman

Get a fresh token from the user you'd like to use. Also, either from the database, or sending a GET request to /api/users, pick out a different user you'd like to 'follow.'

In Postman, send a POST request to localhost:5000/api/users/{userId}/follow/{followId}. (Where userId is the id of the user you have a token for, and followId is the id of the user you want to follow).

You should get a 200 OK response:

FollowTestPostman

You can check the database, to make sure the 'follow event' was added correctly:

FollowWorksDb

If you attempt to 'refollow' the same User (by resending your previous request), you should get a 400 Bad Request response with You already followed this user in the body:

ReFollow204