Which way is better for db handler?

Question

Is it a bad idea for a model class hold the db handler as a property? Example code are as below. I think the second is better, but the first is not so bad in my opinion.

First:

class ActiveModel {
 protected $db;
 public function __construct() {
 $this->db = DbFactory::get('Foo');
 }
 public function save() {
 //use $this->db to do the job;
 ....
 }
}

Second:

class ActiveModel {
 public function save($db = null) {
 if ($db === null) {
 $db = DbFactory::get('Foo');
 }
 //then use $db to do the job;
 ....
 }
}

Answer 1

It is fine and very convenient to keep the database handler as a property. However, you should pass it in the constructor via dependency injection, rather than call it's factory method inside the class. This can ease unit testing when you need to mock a database connection object.

public function __construct($db) {
 $this->db = $db;
}

• xdazz: Yes, you are right. But when dependency injection is not used, I need pass it to constructor every time. When by calling the factory method, I just need change the setting of DbFactory to let it give the mock db connection object.
• bitsoflogic: Also, when doing automated testing, if DbFactory::get('Foo') becomes expensive your test suite will run much slower.