Laravel Schema onDelete set null

Can't figure out how to set proper onDelete constraint on a table in Laravel. (I'm working with SqLite)

$table->...->onDelete('cascade'); // works
$table->...->onDelete('null || set null'); // neither of them work

I have 3 migrations, creating the gallery table:

Schema::create('galleries', function($table)
{
    $table->increments('id');
    $table->string('name')->unique();
    $table->text('path')->unique();
    $table->text('description')->nullable();
    $table->timestamps();
    $table->engine = 'InnoDB';
});

Creating the pictures table:

Schema::create('pictures', function($table)
{
    $table->increments('id');
    $table->text('path');
    $table->string('title')->nullable();
    $table->text('description')->nullable();
    $table->integer('gallery_id')->unsigned();
    $table->foreign('gallery_id')
        ->references('id')->on('galleries')
        ->onDelete('cascade');
    $table->timestamps();
    $table->engine = 'InnoDB';
});

Linking gallery table to a picture:

Schema::table('galleries', function($table)
{
    // id of a picture that is used as cover for a gallery
    $table->integer('picture_id')->after('description')
        ->unsigned()->nullable();
    $table->foreign('picture_id')
        ->references('id')->on('pictures')
        ->onDelete('cascade || set null || null'); // neither of them works
});

I do not receive any errors. Also, even the "cascade" option doesn't work (only on the gallery table). Deleting a gallery deletes all pictures. But deleting the cover picture, wont delete the gallery (for test purposes).

Since even the "cascade" is not triggered, I "set null" is not the problem.

EDIT (workaround):

After reading this article I've changed my schema a bit. Now, the pictures table contains an "is_cover" cell, that indicates whether this picture is a cover on its album or not.

A solution to the original problem is still highly appreciated!

Solution 1:

If you want to set null on delete:

$table->...->onDelete('set null');

First make sure you set the foreign key field as nullable:

$table->integer('foreign_id')->unsigned()->nullable();

Solution 2:

In laravel 8 you can use:

$table->foreignId('forign_id')->nullable()->constrained("table_name")->cascadeOnUpdate()->nullOnDelete();

Reference

The different options are declared in class Illuminate\Database\Schema\ForeignKeyDefinition (see source).