Error in adding foreign key in laravel - laravel

Question

I am beginner in laravel. I am having problem in adding foreign key in laravel. I tried but I can't find the error.
[Illuminate\Database\QueryException]
SQLSTATE[HY000]: General error: 1005 Can't create table laravel_home1
#sql-4b8_2a (errno: 150 "Foreign key constraint is incorrectly formed")
(SQL: alter table `posts` add constraint
`posts_comment_id_foreign` foreign key (`comment_id`) references
`comments` (`id`))
post table migration code
public function up()
{
Schema::create('posts', function (Blueprint $table) {
$table->increments('id');
$table->string('title');
$table->string('content');
$table->integer('comment_id')->unsigned();
});
Schema::table('posts', function ($table) {
$table->foreign('comment_id')
->references('id')
->on('comments');
});
}
comments table migration code
public function up()
{
Schema::create('comments', function (Blueprint $table) {
$table->increments('id');
$table->string('comment');
$table->timestamps();
});
}
public function down()
{
Schema::drop('comments');
}

Answer 1

Problems with adding foreign key in laravel come with 3 reasons:
You have already done some rollbacks or migrated the same migration file multiple times and they are saved in cache and thus causing the problem
You forgot to put ->unsigned(); at the end of that index.
The table with primary key which is later used elsewhere as a foreign key is not migrated previously.
Either way try to put ->unsigned(); at the end like this
$table->integer('item_id')->unsigned();
$table->foreign('item_id')->references('id')->on('items');
and then run composer dump-autoload
and then php artisan migrate
and this should work!
UPDATE
I have found what is wrong with your migration:
Replace this:
public function up()
{
Schema::create('posts', function (Blueprint $table) {
$table->increments('id');
$table->string('title');
$table->string('content');
$table->integer('comment_id')->unsigned();
});
Schema::table('posts', function ($table) {
$table->foreign('comment_id')
->references('id')
->on('comments');
});
}
With this:
public function up()
{
Schema::create('posts', function (Blueprint $table) {
$table->increments('id');
$table->string('title');
$table->string('content');
$table->integer('comment_id')->unsigned();
$table->foreign('comment_id')
->references('id')
->on('comments');
});
}