save one to one relationship. foreign keys in both tables

Question

I have two tables as follow:

CREATE TABLE pets(
      id int NOT NULL AUTO_INCREMENT,
          user_id int,
          any_data varchar(255),
      foreign key (user_id) references users(id),
      primary key(`id`)
);

CREATE TABLE users(
      id int NOT NULL AUTO_INCREMENT,
          pet_id int,
          any_data varchar(255),
      foreign key (pet_id) references pets(id),
      primary key(`id`)
);

And my models have the next:

USERS:

public function relatedPet() {
    return $this->hasOne("Pet", "pet_id");
}

PETS:

public function relatedUser() {
    return $this->belongsTo("User", "user_id ");
}

I want to save an User and relate to an existent pet, but i don't know how to do that:

$user= new User(array("any_data"=>"Hi, this is a test"));
$pet = Pet::find(1);

How can I create the relation between the two objets?

Answer 1

First your users table does not need a pet_id. Drop it. Then

Users Model

public function pet()
{
    return $this->hasOne('App\Pet'); // Changed form hasMany to hasOne
}

Pet Model

public function user()
{
    return $this->belongsTo('App\User');
}

Now create a new User

$user = \App\User::create($data); // You need to set $fillable property
$pet = \App\Pet::findOrfail($id)
$pet->user()->associate($user);
$pet->save();

Examples:

$user = \App\User::findOrFail($id);
$pet = $user->pet

// Inserting a new user and a pet
$anotherUser = \App\User::create($data);
$anotherPet = new \App\Pet($data);
$anotherUser->pet()->save($anotherPet);

$pet = \App\Pet::findOrFail($id);
$user = $pet->user

// Inserting a new pet, a user and then associating them
$anotherPet = \App\Pet::create($data);
$anotherUser = \App\User::create($data);
$anotherPet->user()->associate($anotherUser);
$anotherPet->save()