在Eloquent中连接具有多个表的数据透视表

class User extends Model
{
    public function roles()
    {
        return $this->belongsToMany(Role::class);
    }
}

class Role extends Model
{
    public function permissions()
    {
        return $this->belongsToMany(Permission::class);
    }
}

Schema::create('role_user', function (Blueprint $table) {
    $table->unsignedBigInteger('user_id');
    $table->unsignedBigInteger('role_id');

    $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
    $table->foreign('role_id')->references('id')->on('roles')->onDelete('cascade');
});

$user = User::find(1);
$role = Role::find(1);

$user->roles()->attach($role->id);

$user->roles()->sync([1, 2, 3]); // 更新关联关系

class User extends Model
{
    public function roles()
    {
        return $this->belongsToMany(Role::class)->withPivot('expires_at');
    }
}

$user = User::find(1);
$role = $user->roles()->first();

$expiresAt = $role->pivot->expires_at;