Could someone give me an example of how I make a relationship in the migration and model, where this relationship results in a table with external ids.
Example:
A reseller by having no or n addresses, and an address can only have one resale.
This relationship would result in a resale_address table 
I'm using version 5.7 of Laravel.
We need to define the third table, which is the PivotTable. Here is an example
Now, set the following scheme in the migration file.
public function up()
{
Schema::create('category_product', function (Blueprint $table) {
$table->increments('id');
$table->integer('category_id')->unsigned();
$table->integer('product_id')->unsigned();
});
}
Set relationships:
class Category extends Model
{
public function products(){
return $this->belongsToMany(Product::class);
}
}
The other
class Product extends Model
{
public function categories()
{
return $this->belongsToMany(Category::class);
}
}
To create a product, do
public function create(Request $request)
{
$product = new Product;
$product->name = 'God of War';
$product->price = 40;
$product->save();
$category = Category::find([3, 4]);
$product->categories()->attach($category);
return 'Success';
}