Laravel Many To Many Relationship between Three Models - laravel

Question

I want to create a relationship between the three models. My models are
Users
-- Database Structure
id
name
---
Books
-- Database Structure
id
name
BookShelf
-- Database Structure
id
name
1: User has many books and book belongs to many users
2: User's book belongs to one BookShelf and user's BookShelf has many books.
How can I define the relationship between these three models? I am building an application something like Goodreads.

Answer 1

You have a many to many relationship between your User and Book, as well as a many to many between your Book and BookShelf.
This type of relationship is managed by a pivot table behind the scenes, so you will require two pivot tables.
Pivot between User and Book
Create your migration
php artisan make:migtration create_book_user_table
Define your relationship
public function up()
{
Schema::create('book_user', function (Blueprint $table) {
$table->id();
$table->timestamps();
$table->foreignId('user_id')->constrained();
$table->foreignId('book_id')->constrained();
});
}
Pivot between Book and BookShelf
Create your migration
php artisan make:migtration create_book_book_shelf_table
Define your relationship
public function up()
{
Schema::create('book_user', function (Blueprint $table) {
$table->id();
$table->timestamps();
$table->foreignId('book_id')->constrained();
$table->foreignId('book_shelf_id')->constrained();
});
}
With the pivot tables create you can add the relationships to your models.
User
public function books()
{
return $this->belongsToMany(Book::class);
}
Book
public function users()
{
return $this->belongsToMany(User::class);
}
public function bookshelves()
{
return $this->belongsToMany(BookShelf::class);
}
BookShelf
public function books()
{
return $this->belongsToMany(Book::class);
}
Now you have your relationships, you can access them on your User. As an example:
Route::get('/', function () {
$user = User::where('id', 1)->with(['books', 'books.bookshelves'])->first();
return view('user', compact('user'));
});
user.blade.php
<h3>{{ $user->name }}</h3>
<h4>Books</h4>
#foreach ($user->books as $book)
<h5>{{ $book->name }}</h5>
<p>Can be found on #choice('shelf|shelves', $book->bookShelves()->count())</p>
#foreach ($book->bookShelves as $shelf)
<li>{{ $shelf->name }}</li>
#endforeach
#endforeach
The above would iterate over each Book for the $user and then iterate over each of the BookShelves that Book is related to.
Update
If a Book can only belong to one Bookshelf, you need to alter your books table.
public function up()
{
Schema::create('books', function (Blueprint $table) {
$table->id();
$table->timestamps();
$table->string('name');
$table->foreignId('bookshelf_id')->constrained('book_shelves');
});
}
You will also need to alter the relationship on your Book model:
public function bookshelf()
{
return $this->belongsTo(BookShelf::class);
}
This way a Book can now only belong to one Bookshelf.
If a User can only have one Bookshelf, again you need to alter your book_shelves table:
public function up()
{
Schema::create('book_shelves', function (Blueprint $table) {
$table->id();
$table->timestamps();
$table->string('name');
$table->foreignId('user_id')->constrained();
});
}
Then add the relationship to your User.
public function bookshelf()
{
return $this->hasOne(BookShelf::class);
}
You should then be able to access the Bookshelf for a User directly.
$user->bookshelf->books

Answer 2

1: User has many books and book belongs to many users
User has a Many To Many relationship with Book
// User model
public function books()
{
return $this->belongsToMany(Book::class, 'book_user');
}
Book has a Many To Many relationship with User
// Book model
public function users()
{
return $this->belongsToMany(User::class, 'book_user');
}
2: User's book belongs to many BookShelf and BookShelf has many books.
Book has a Many To Many relationship with Bookshelf
// Book model
public function bookshelves()
{
return $this->belongsToMany(Bookshelf::class, 'book_bookshelf');
}
Bookshelf has a Many To Many relationship with Book
// Bookshelf model
public function books()
{
return $this->belongsToMany(Book::class, 'book_bookshelf');
}
You'd need two pivot tables.
book_user
column
migration
id
$table->id()
book_id
$table->foreignId('book_id')->constrained('books')
user_id
$table->foreignId('user_id')->constrained('users')
book_bookshelf
column
migration
id
$table->id()
book_id
$table->foreignId('book_id')->constrained('books')
bookshelf_id
$table->foreignId('bookshelf_id')->constrained('bookshelves')

Answer 3

Let's start from first task:
1: User has many books and book belongs to many users
In this case it is many-to-many relationships. To implement this setup you need users table like this:
Users: id, name, someotherdata
then you need books table:
books: id, name, bookdata
and then you need the third table to connect them many to many:
users_books: id, book_id, user_id
In this case when you need all books which belongs to one user you can select from users_books where user_id=someuserid and join it with books table and you will receive all books which belongs to some user.
Visa versa you can receive all users who posses some particular book.
2: User's book belongs to one BookShelf and user's BookShelf has many books.
For this you would have to create table bookshelfs: id, name
And add foreign key to books table as bookshelf_id
Then your books table will look like this:
books: id, name, bookdata, bookshelf_id.
So when you need to get all books from shelf just filter select from books where bookshelf_id = someid