save one to one relationship. foreign keys in both tables - laravel

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()