gistfile1.php

<?php

Schema::table('users', function ($table) {

});

Schema::table('posts', function ($table) {

    $table->foreign('user_id')
        ->references('id')->on('users');
});

Schema::table('comments', function ($table) {

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