Laravel 5.5 relation Many to many

Question

I'm doing my first project with laravel 5.5 aç and now I'm establishing models and relationships

My project consists of a social network of video games.

The two models that I want to relate are the following, it would be a many-to-many relationship:

the genre of the game:

class Genero extends Model
{
    protected $primaryKey = "cod";
    public $incrementing = true;
    protected $keyType = "int";

    protected $table = "generos";
    protected $fillable = ["cod","nombre"];
    //public $timestamps = false;

    public function juegos(){
        return $this->belongsToMany('App\Juego',"juegosGeneros","codGenero","codJuego");
    }
}

And the Game

class Juego extends Model
{
    protected $primaryKey = "codJuego";
    public $incrementing = false;
    protected $keyType = "int";

    protected $table = "juegos";
    protected $fillable = ["cod", "nombre"];
    //public $timestamps = false;

    public function generos(){
        return $this->belongsToMany('App\Genero',"juegosGeneros","codJuego","codGenero");
    }
}

My db tables are that:

CREATE TABLE juegos(
cod INT AUTO_INCREMENT,
nombre VARCHAR(50),
PRIMARY KEY (cod)
);

CREATE TABLE generos(
cod INT AUTO_INCREMENT,
nombre VARCHAR(50),
PRIMARY KEY (cod)
);

CREATE TABLE juegosGeneros(
codJuego INT,
codGenero INT
);

My problem: I have inserted data in the tables and when retrieving them

<?php
        $juego = \App\Juego::where("cod","1")->first();
        dd($juego->generos);
?>

they returned me an empty array

Collection {#188 ▼
  #items: []
}

Observing the queries made to the database laravel do this:

select `generos`.*, `juegosGeneros`.`codJuego` as `pivot_codJuego`, `juegosGeneros`.`codGenero` as `pivot_codGenero` 
from `generos` 
inner join `juegosGeneros`
on `generos`.`cod` = `juegosGeneros`.`codGenero` where `juegosGeneros`.`codJuego` is null

Idont know the reason of this condition, and I think that is the problem

 where `juegosGeneros`.`codJuego` is null

I really appreciate your help

Answer 1

You set the wrong primary key:

class Juego extends Model
{
    protected $primaryKey = "cod";
}