Eloquent Relationship returning empty array - laravel-5

Question

I'm New to laravel and I'm trying to achieve something very basic stuff but still getting stuck.
I have two models namely Post.php and Like.php
I'm trying to fetch all the likes linked to a post using eloquent relationship but it is returning an empty array. Here is my code-
Post.php
public function likes(){
return $this->hasMany('App\Like');
}
Route.php
Route::get('/', function(){
$posts = Post::all()->sortByDesc("post_id");
return view('index')->with(['posts' => $posts]);
});
View.blade.php
#foreach($posts as $post)
{{ $post->likes }}
#endforeach
What am I doing wrong here?
Update-
likes table migration
public function up()
{
Schema::create('likes', function (Blueprint $table) {
$table->increments('like_id');
$table->integer('post_id')->unsigned();
$table->integer('user_id')->unsigned();
$table->foreign('post_id')->references('post_id')->on('posts')->onDelete('cascade');
$table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
$table->timestamps();
});
}
Post Migration
public function up()
{
Schema::create('posts', function (Blueprint $table) {
$table->increments('post_id');
$table->integer('user_id')->unsigned();
$table->string('post_message');
$table->timestamps();
$table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
});
}
Post Model
<?php
namespace App;
use Illuminate\Database\Eloquent\Model;
class Post extends Model
{
public function user(){
return $this->belongsTo('App\User');
}
public function likes(){
return $this->hasMany('App\Like');
}
}

Answer 1

Laravel expects the primary key to be id, but you are using the custom post_id.
Specify it in your model and adjust the relationship:
class Post extends Model {
protected $primaryKey = 'post_id';
public function likes() {
return $this->hasMany('App\Like', 'post_id');
}
}