Answers for "define foreign key without creating table laravel 9"

foreign key in laravel migration

$table->unsignedBigInteger('user_id');
$table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');

laravel foreign key

Schema::table('posts', function (Blueprint $table) {
    $table->unsignedBigInteger('user_id');

    $table->foreign('user_id')->references('id')->on('users');
});
OR
Schema::table('posts', function (Blueprint $table) {
    $table->foreignId('user_id')->constrained();
});

Laravel create foreign key column in migration

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