1

I am writing a database interaction layer in PHP for MySQL. But I think this is a general OOP question (see last line).

I have a basic dbTables class. And it has a 

public static function getBy($method='name', $value) {
        // Gets flat table array of db Tables matching by $method == $value
        // later could implement some lookup tables.
        $allowed = array('name');
        $query_format = SHOW TABLES LIKE '%s'";
        if(in_array($method,$allowed)) {
            dbConnection::connect(MAIN_DB); // makes db connection
            $safe_value = mysql_real_escape_string($value);
            // MAY want to change this query to a SCHEMA query in CHILD classes
            $sql = sprintf($query_format,$safe_value);
            // e.g. $sql = "SHOW TABLES LIKE '$safe_value'";
            $result = mysql_query($sql);
            if($result === false) {
                debug::add('errors', __FILE__, __LINE__, __METHOD__,"Query Error for query '$sql'. MySQL said: " . mysql_error());
            }
            while($row = mysql_fetch_row($result)) {
                $db_table = new static($row[0]); // creates instance of $this class
                $object_array[] = $db_table; // add to $object_array for return value
            }
        } else {
            debug::add('errors',__FILE__, __LINE__, __METHOD__, ' - Wrong method: ' . $method . '. Currently allowed: ' . print_r($allowed,true));
            return false;
        }
    return $object_array;
    // END public static function getBy($method='name', $value)
    }

But child classes will different queries to get information. They will have other allowed $methods for searching.

Here is my solution, but I don't know if it is good practice and if it will lead to more pain later. Rather than override this function in every child class, I can create a set of private static properties that will act as modifiers for the function.

Like so:

    protected static $get_by_methods = array('name'); // array('name','id','frontend_name'…) in CHILDREN
    protected static $get_by_query_format = "SHOW TABLES LIKE '%s'"; // for sprintf. Changes in children
    protected static $get_by_handles_arrays = false; // true in CHILDREN
    protected static $get_by_query_format_array = " SELECT * FROM %s` WHERE `$method` IN ($safe_values)"; // used in CHILDREN ONLY

    public static function getBy($method, $value) {
        $allowed = self::$get_by_methods;
        $query_format = self::$get_by_query_format;
        $handle_arrays = self::$get_by_handles_arrays; // false here,,, true in children
        $query_format_array = self::$get_by_query_format_array; // used in children
        if(is_array($value) && $handle_arrays === true) {
            return false; // in child class, $handle_arrays can be set to true outside of function
                // without rewriting function. just change the static property
        }
        if(in_array($method,$allowed)) {
            dbConnection::connect(MAIN_DB);
            if(!is_array($value)) { // handle string values
                $safe_value = mysql_real_escape_string($value);
                $sql = sprintf($query_format,$safe_value);
            } else {
                // arrays used only in children
e.g. 
$safe_values = mysql_real_escape_string(implode(',',$value)); // convert to string
                $sql = sprintf($query_format_array,$safe_values); // used in children
            }
            $result = mysql_query($sql);
            if($result === false) {
                debug::add('errors', __FILE__, __LINE__, __METHOD__,"MySQL Error num " . mysql_errno() . " for query [$sql] - MySQL said: " . mysql_error());
            }
            while($row = mysql_fetch_row($result)) {
                $db_table = new dbTables($row['name']);
                $object_array[] = $db_table;        
            }
        } else { // if bad method chosen above
            debug::add('errors',__FILE__, __LINE__, __METHOD__, ' Wrong method: ' . $method . '. Must use one of these: ' . print_r($allowed,true));
            return false;
        }
    return $object_array;
    // END public static function getBy($method='name', $value)
    }

To sum up, doing this will allow me to never override the getBy() method. I will only have to override the protected static properties that go with it. For DRY (don't repeat yourself), this seems good. I will only have to write 4 lines of code instead of 20+ over and over again. But I am new at this and don't know if this might be a horrible mistake for some other reason.

Is it safe and good practice to take the inheritance overriding out of the methods and put it into helper properties?

4

1 に答える 1

0 
 $allowed = array('name');
 $query_format = SHOW TABLES LIKE '%s'";

動作を上書きするには、子クラスでこれにアクセスする必要があるため、クラスプロパティに属しているようです。

子クラスでは、動作を上書きするか、次のような親キーワードを使用して同じものを使用できます

$allowed = parent::$allowed;

$allowed は親から継承された値を持つようになりました。

メソッドも同様です。親メソッドを呼び出したい場合は、parent キーワードを使用します。

親::getBy(); あなたの子供のクラスで。DRY (同じことを繰り返さない) 原則を常に覚えておいてください。あなたの場合、親クラスと子クラスでコードを繰り返しています。代わりに、親を使用して子クラスの親メソッドを呼び出します。たとえば、子クラスで

public function getBy()
{
    parent::getBy();
}

子の getBy() が親から継承されるようになりました。オーバーライドする必要があるのはクラス プロパティだけです。

于 2012-05-09T08:06:59.627 に答える