与laravel中三个表的关系

Question

I need help to get data from my database. I have the following models:

-User
--Id
--Name

-Book
--Id
--Name

-List
--Id
--Title

-BookList
--id
--List
--Book
--User

I am using eloquent and I would like do get data following the structure below:

-User
--List 1
--- Book 1
--- Book 2
--List 2
--- Book 1
--- Book 3

In other words, a user with multiple lists of books. In the User.php model I made the following relationship:

public function lists ()
{
  return $ this-> belongsToMany (
    List :: class, // related
    'books_lists', // table
    'user', // foreign pivot key
    'list' // related pivot key
  );
}

public function books ()
{
   return $ this-> belongsToMany (
      Book :: class, // related
      'books_lists', // table
      'user', // foreign pivot key
      'book' // related pivot key
   );
}

This way I get the following return:

-User
--List 1
--List 2
--Book 1
--Book 3

What kind of relationship I need to do to get data in desired structure?

Thank you.

Answer 1

The best structure would be to merge the list and booklist table (since every book list can only have one title anyway)

-Users
--id
--name

-books
--id
--name

-book_list
--book_id
--list_id

-lists
--id
--title
--user_id

In the User.php

public function lists ()
{
  return $this->hasMany(List::class);
  //no need to define the foreign keys if you name the tables and fields like above
}

in the List.php

public function books ()
{
  return $this->belongsToMany(Book::class);
  //no need to define the foreign keys if you name the tables and fields like above
}

now you can get the results with this

$user = User::with('lists.books')->find($userId);

the result will be as follow

-user
--List 1
---Book 1
---Book 2
--List 2
---Book 1
---Book 4

Answer 2

A book can be added to multiple list, right? Your database structure can be better, but I assume your ERD is fixed by designer/leader. So just do it my instruction:

Add this relation to User Model(User.php):

public function lists ()
{
  return $this->belongsToMany (
    List::class, // related
    'books_lists', // table
    'user', // foreign pivot key
    'list' // related pivot key
  );
}

And this relation to List Model(List.php):

public function books ()
{
   return $this->belongsToMany (
      Book::class, // related
      'books_lists', // table
      'list', // foreign pivot key
      'book' // related pivot key
   )->withPivot(["user"]);
}

to return

$user = User::with(['lists.books'=> function($q)use($id){
$q->wherePivot('user', '=', $id);}])->first();
dd($user->toArray())

---

But it's better to change your structure to:

-User
--Id
--Name

-Book
--Id
--Name

-List
--Id
--Title

-BookList
--id
--List
--Book

-UserList
--List
--User