Laravel每个用户只有一个friend_id

CREATE TABLE users (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255) NOT NULL
);

CREATE TABLE friends (
    id INT PRIMARY KEY AUTO_INCREMENT,
    user_id INT UNIQUE NOT NULL,
    friend_id INT NOT NULL,
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (friend_id) REFERENCES users(id)
);

class User extends Model
{
    public function friend()
    {
        return $this->hasOne(Friend::class);
    }
}

class Friend extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

ALTER TABLE friends ADD UNIQUE (user_id);

use Illuminate\Validation\Rule;

$validator = Validator::make($request->all(), [
    'friend_id' => [
        'required',
        Rule::unique('friends')->where(function ($query) use ($userId) {
            return $query->where('user_id', $userId);
        }),
    ],
]);

$user = User::find($userId);

$friendData = [
    'friend_id' => $friendId,
];

$validator = Validator::make($friendData, [
    'friend_id' => [
        'required',
        Rule::unique('friends')->where(function ($query) use ($userId) {
            return $query->where('user_id', $userId);
        }),
    ],
]);

if ($validator->fails()) {
    return response()->json(['error' => $validator->errors()], 400);
}

$friend = new Friend($friendData);
$user->friend()->save($friend);

return response()->json(['message' => 'Friend set successfully'], 200);