The first parameter in the Book::where method should be the column name. For example author_id instead of author->id. Given that a publisher can have many authors a query could look like this:

Book::where('author_id', $author->id)
    ->whereIn('author_id', function(Builder $query) {
        $query->select('id')->from('authors')->where('publisher_id', $pub->id);
    }
)->get();

This first selects all books by the given author. Then, in the whereIn method, it adds the constraint that the author also must belong to the given publisher.

Let me know if that works!

It doesn't work. (I think you modified the code, I will try it).

You will need a way to keep track of which books belongs to author X.

Your database structure would look like this

Table: books
====================
ID: 1
title: "Some awesome book"
author_id: 1
publisher_id: 1
---------------------------------------
ID: 2
title: "Laravel for beginners"
author_id: 2
publisher_id: 2


Table: authors
====================
ID: 1
name: "John Doe"
--------------------------------------
ID: 2
name: "Jenny Doe"



Table: publishers
====================
ID: 1
Name: "Publisher 1"
---------------------------------------
ID: 2
Name: "Publisher 2"

Let's say we wan't all books that are written by "John Doe" and published by "Publisher 1", our query would look like:

$books = Book::where('author_id', '=', 1)->where('publisher_id', '=', 1)->get();

So you recommend to add a publisher_id field to the books table.

But, every book has only one author, and every author has only one publisher. Isn't there a way to find the publishers of some books without adding a publisher field?

Will an extra publisher field in the books table increase the performance of the query?

Thanks..

I'm pretty sure books from the same author could have different publishers (In real life). So why limit your system to only 1 publisher per author? What you are trying to achieve is pretty easy with the Database structure in my previous reply.

To make your code i little bit more beautiful, i would make the Book model like this:

class Book extends Eloquent{

    public function author(){
        return $this->belongsTo('Author', 'author_id', 'id');
    }

    public function publisher(){
        return $this->belongsTo('Publisher', 'publisher_id', 'id');
    }

}

And then use it like this:

$book = Book::with( array( 'author', 'publisher') )->find(1);

echo $book->author->name; // Outputs: "John Doe"
echo $book->publisher->name; // Outputs: "Publisher 1" 

You are right, authors can have different publishers. But I just made an anology with the publisher-author-book model to make it easy to express my problem. My real models have different names. And in my model, each "author" has only one "publisher".
So, I want to repeat my question: Will an extra publisher field in the books table increase the performance of the query?

Fatihir, try the query I wrote again and see if that works. It should!