https://laravel.com/docs/5.5/eloquent-relationships#polymorphic-relations
In this official example of polymorphic relations, the following table structure has been used:
posts
id - integer
title - string
body - text
videos
id - integer
title - string
url - string
comments
id - integer
body - text
commentable_id - integer
commentable_type - string
How do I set commentable_id as a foreign key in such a way, so that when a post or a video is deleted, all comments associated with it will also be deleted?
The example shown here : https://laravel.com/docs/5.5/migrations#foreign-key-constraints
$table->foreign('user_id')
->references('id')->on('users')
->onDelete('cascade');
makes use of the on() method by passing a single table name, users. What if I wanted to apply this on two tables, posts and videos?
Okay, after googling a bit, I realized why it is not possible to apply foreign key on polymorphic relations. I came across this laracasts discussion
https://www.laracasts.com/discuss/channels/eloquent/polymorphic-relations-on-delete/replies/353658
and decided to be explicit on the controller's destroy() method. Any alternative solution will be greatly appreciated.
In Laravel 8, you can use the morphs() method on the table.
From the docs:
This method is intended to be used when defining the columns necessary for a polymorphic Eloquent relationship. In the following example, taggable_id and taggable_type columns would be created:
$table->morphs('taggable');
Just a quick note that the $table->morphs('taggable') method is essentially just an alias for $table->string('taggable_type'); $table->unsignedInteger('taggable_id').
It does not create any foreign key constraints. To the best of my knowledge, these don't work with polymorphic relationships.
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