Laravel 4.1.2

Exception.txt

SQLSTATE[HY000]: General error: 1 ambiguous column name: id
(SQL: select * from "categories" inner join "category_posts" on "categories"."id" = "category_posts"."category_id" where "category_posts"."post_id" = 1 and "id" = 1 limit 1)

ModelA.php

<?php

class Post extends \Illuminate\Database\Eloquent\Model
{
    public function categories()
    {
        return $this->belongsToMany('Category', 'category_posts');
    }
}

ModelB.php

<?php

class Category extends \Illuminate\Database\Eloquent\Model
{
    public function posts()
    {
        return $this->belongsToMany('Post', 'category_posts');
    }
}

test.php

<?php

class MyGreatTest extends PHPUnit_Framework_TestCase
{
    public function testAssociation()
    {
        $post = Post::create();
        $category = Category::create();
        
        $post->categories()->attach($category);
        
        $this->assertCount(1, $post->categories()->where('id', $category->id));
    }