how to define a string datatype as foreign key in laravel migration code example

Example 1: 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();
});

Example 2: foreign key string laravel

Schema::table('portfolios', function (Blueprint $table) {
            $table->string('filter_alias');
            $table->foreign('filter_alias')->cascadeOnDelete()->references('alias')->on('filters');
        });