laravel migration add foreign key constraint to existing column code example
Example 1: foreign key laravel migration
$table->foreign('column_name')->references('id')->on('table_name')->onDelete('cascade');
Example 2: laravel migration foreign key 5.6
Schema::table('posts', function (Blueprint $table) {
$table->unsignedInteger('user_id');
$table->foreign('user_id')->references('id')->on('users');
});