PHP OOP- 对象交互

Question

I am currently working in PHP and have begun to utilise classes- I am learning a lot, however I am yet to have my "penny drop" moment- I am struggling with object interaction.

I'd really appreciate some clarification in regards to how one object should interact with another. As a very basic example if I have a database object which handles connecting and querying a database, how should other classes access the results of queries performed by the database object?

From my understanding so far, I can see 2 options. Either the query results within the database class are accessible publicly and are passed to other objects as arguments...

$databaseObject = new DatabaseObject;
$databaseObject->query("query goes here");

$newObject = randomObject;
$newObject->doStuff($databaseObject->query())

Or objects which rely on query results instantiate new database objects within themselves and therefore the results are contained within that object.

class databaseConnection {

    public $queryResults;

    function __construct {
        connect to database...
    }

    function query {
        perform queries...
        $this->queryResults = query results
    }
}

class NewObject
{
    function doStuff() {
        $db = new databaseConnection
        do stuff with $db->queryResults
    }
}

Option 1 seems wrong as properties in the database class are available globally, whereas option 2 seems to contradict the idea that classes should only hold methods and properties relating to the object they define.

I could think of many other examples. If I create a class responsible for managing a user throughout a system, yet classes responsible for other tasks need to know what privilege level a user has, do I make that property within the user class global and pass it to other classes? Do the other classes instantiate new user objects?

Any help much appreciated.

Answer 1

Either the query results within the database class are accessible publicly

This (for me) is the key to the answer. If you set or change a value in the instance, this rather implies that you want to set the value in the underlying dataset (although you might consider defering the write). Note that the magic methods allow you to associate actions with get and set operations implicitly. But not every query is updateable. If your sql is baked in, then you can determine the updatability at design time.

Also, I suggest that your query object has a set of record objects associated with it where you interact with the underlying data. Bundling the connection functionality in the same object as the query only really makes sense if it is a factory (supporting multiple queries) and creating query result objects. And the query (result) object should probably implement the iterator interface.

Both pdo and mysqli seperate the connection, query and results into seperate objects - for good reason.

Answer 2

class Connection {

  public static $conn;

  public static function getInstance() {
     if (!self::$conn) {
         self::$conn = new Connection();
     }

     return self::$conn;
  }

  public function query() {
      echo "run your query here using self::\$conn object";
  }
}

class Person {

    public function doStuff() {
        $conn = Connection::getInstance();
        $results = $conn->query();
    }
}

$person = new Person();
$person->doStuff();

Firstly, you want to get your database connection only one time rather then opening it every time.

Secondly, using the same database connection object you can run multiple queries as shown in the above example.

You will always get a single connection no matter how many other classes you use.