How to determine pivot-table name in belongToMany relationship in Laravel?

Question

I am having the issue of simply trying to determine the correct name to give to the intermediary table used for many to many relationships in Laravel.

I received the following error upon attempting to access an eloquent relationship:

$product->categories; Illuminate/Database/QueryException with message 'SQLSTATE[42S02]: Base table or view not found: 1146 Table 'dolstore-laravel.category_product' doesn't exist (SQL: select categories.*, category_product.product_id as pivot_product_id, category_product.category_id as pivot_category_id from categories inner join category_product on categories.id = category_product.category_id where category_product.product_id = 1)'

My migration is written as follows:

    public function up()
    {
        Schema::create('categories', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->string('name')->unique();
            $table->timestamps();
        });

        Schema::create('product_category', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->unsignedBigInteger('product_id');
            $table->unsignedBigInteger('category_id');
            $table->timestamps();

            $table->unique(['product_id', 'category_id']);

            $table->foreign('product_id')->references('id')->on('products')->onDelete('cascade');
            $table->foreign('category_id')->references('id')->on('categories')->onDelete('cascade');
        });
    }

It seems that I provided the incorrect name of product_category when it should have been category_product. What is the rule governing this? In another example where I actually succeeded following a tutorial on Laracasts, my migration was written as follows:

    public function up()
    {
        Schema::create('tags', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->string('name')->unique();
            $table->timestamps();
        });
        //Pivot Table
        // article_tag

        Schema::create('article_tag', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->unsignedBigInteger('article_id');
            $table->unsignedBigInteger('tag_id');
            $table->timestamps();

            $table->unique(['article_id', 'tag_id']);

            $table->foreign('article_id')->references('id')->on('articles')->onDelete('cascade');
            $table->foreign('tag_id')->references('id')->on('tags')->onDelete('cascade');
        });
    }

Therefore it does not appear to be related to the order in which the tables are created or the migration within which the pivot table is defined.

Thank you for helping me understand this.

Answer 1

When you are not passing the second parameter of your belongsToMany relationship in your model. Therefore, Laravel is expecting that you had used its naming convention while creating pivot table. How do they check it ? Lets say you have a products and categories table.

Now, laravel will expect that you had created your pivot table on alphabetical order, they will expect that your pivot table was named category_product considering that the first letter of your category which is 'c' is first than to your table product first letter is 'p'. That is why in your article_tag pivot table it worked right ?

Let say your had created your pivot table by not following its naming convention. then you have to pass it as second parameter in your m to m relationship, like this.

public function product_categoreis() [
   return $this->belongsToMany('App\Category', 'product_category');
}