Laravel UUID为主键，ID为外键

Question

I've defined a uuid as primary key, and would like to use id (auto increment) as foreign key to define relationships.

Both Posts and Comments have in their migration:

$table->uuid('uuid')->primary();
$table->bigInteger('id');

Their models have:

protected $primaryKey = 'uuid';
protected $keyType = 'string';
public $incrementing = false;

And the comments migration has

$table->bigInteger('post_id')->unsigned();
$table->foreign('post_id')->references('id')->on('posts')->onDelete('cascade');

But if I run the migration I get General error: 1215 Cannot add foreign key constraint (SQL: alter table `comments` add constraint `comments_post_id_foreign` foreign key (`post_id`) references `posts` (`id`) on delete cascade) of which I'm not sure why it's happening? Before adding the UUID logic it was working fine so I'm sure I've made a mistake there, but I'm not sure what as the error is generic.

Answer 1

Adding a foreign key requires the referenced key and the foreign one to have the same type and sign. According to your migrations, both posts.id and comments.id are signed bigints but you are trying to add a foreign key to a un signed bigint.

In your migrations for posts and comments , change

$table->bigInteger('id');

to

$table->bigInteger('id')->unsigned();

and migrate them again.

Answer 2

Give this a try.

$table->foreignId('post_id')->constrained('posts')->onDelete('cascade');

Answer 3

You can try this.

$table->foreignUuid('post_id')->constrained()->onDelete('cascade');

You can have a look at the method which is inside the vendor/laravel/framework/src/Illuminate/Database/Schema/Blueprint.php

 /**
 * Create a new UUID column on the table with a foreign key constraint.
 *
 * @param  string  $column
 * @return \Illuminate\Database\Schema\ForeignIdColumnDefinition
 */
public function foreignUuid($column)
{
    return $this->columns[] = new ForeignIdColumnDefinition($this, [
        'type' => 'uuid',
        'name' => $column,
    ]);
}