调用未定义的方法Illuminate \ Database \ Schema \ MySqlBuilder :: dropForeign（）

class CreateCommentsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('comments', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->string('email');
            $table->text('comment');

            $table->boolean('approved');
            $table->integer('post_id')->unsigned();
            $table->timestamps();
        });

        Schema::table('comments', function (Blueprint $table) {
            $table->foreign('post_id')->references('id')->on('posts');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropForeign(['post_id']);
        Schema::dropIfExists('comments');
    }
}

This is what my migration class looks like, i have been trying to delete the table from the database but it throws me an error.

Error

Call to undefined method Illuminate\Database\Schema\MySqlBuilder::dropForeign()

I have gone through the documentation but it doesnot seem to be of much help.

could anyone please point out my mistake and what would be the solution ?

Just so you know , i am new to laravel.Go easy on me.Thanks!.

dropForeign needs to be called under Schema::table with a Blueprint object,

Schema::table('comments', function (Blueprint $table) {
        $table->dropForeign('comments_post_id_foreign');
    });

This follows the naming convention of <table_name>_<foreign_table_name>_<column_name>_foreign.

OR

Schema::table('comments', function (Blueprint $table) {
        $table->dropForeign(['your_key_name']);
    });

You're using wrong syntax. It should be:

Schema::table('comments', function (Blueprint $table) {
    $table->dropForeign('comments_post_id_foreign');
});

https://laravel.com/docs/5.3/migrations#foreign-key-constraints