Question

I am a little bit confused how to implement the following OO structure in PHP. I have a class ‘User‘ and a class ‘UserGroup‘ a ‘User’ is part of one ‘UserGroup’. In the database the user table has a field ‘user_group_id‘. What is a good and ‘server friendly’ way of implementing this? Do I create an instance of UserGroup inside my user class or do i only save the user_group_id in a variable?

Note: not all methods are shown in the examples.

Option 1

class User
{
    private $userGroupId;
    public function setGroupId($userGroupId)
    {
        $this->userGroupId = $userGroupId;
    }
}

Option 2

class User
{
    private $userGroup;
    public function setGroup($userGroupId)
    {
        $this->userGroup = new UserGroup($userGroupId);
    }
}

My problem with option 2 is that it might consume more server resources because it creates a totally new instance of a usergroup for every user. But I am not sure about this and I can’t find any info about this.

My question: what is good implementation?

Answer 1

This is typical has-a relationship between User and UserGroup. In another words User has a UserGroup. So I think class User should have reference to UserGroup. If you are too worried and/or limited in resources you can create instance of UserGroup in User when it’s actually needed.

The implementation will be something like:

class User
{
    private $userGroupId;
    private $userGroup = null;
    public function setGroupId($userGroupId)
    {
        $this->userGroupId = $userGroupId;
    }

    public function getGroup()
    {
        if ($this->userGroup === null)
        {
            $this->userGroup = new UserGroup($this->userGroupId);
        }
        return $this->userGroup;
    }
}