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Review: the MySQLiWrapper and MySQLi_ResultWrapper classes - PHP

In this fifth part of a six-part series on the Iterator, Countable and ArrayAccess SPL interfaces, I implement the rest of the methods declared by the ArrayAccess SPL interface within the “MySQLi_ResultWrapper” class that you saw in a previous part. Once this process is completed, the class will be able to treat records in database result sets as if they were plain array elements.

TABLE OF CONTENTS:
  1. Implementing More Methods of the ArrayAccess SPL Interface
  2. Review: the MySQLiWrapper and MySQLi_ResultWrapper classes
  3. Defining the offsetUnset() method
  4. Finish defining the methods of the ArrayAccess interface
By: Alejandro Gervasio
Rating: starstarstarstarstar / 1
April 12, 2010

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Since my goal in this article is to make the MySQL handling class built in the prior chapter a full implementer of the ArrayAccess SPL interface, first I want to review the definition of this class, along with the one that connects to the database server and runs hard-coded SQL statements.

Having explained that, here’s the source code of the sample class that performs the aforementioned tasks:

class MySQLiWrapper extends MySQLi

{

   

   private static $_instance = NULL;

 

 

   // return Singleton instance of MySQL class

   public static function getInstance(array $config = array())

   {

       if (self::$_instance === NULL)

       {

          self::$_instance = new self($config);

       }

       return self::$_instance;

   }

  

   // private constructor

   private function __construct(array $config)

   {

        if (count($config) < 4)

        {

            throw new Exception('Invalid number of connection parameters');  

        }

       list($host, $user, $password, $database) = $config;

       parent::__construct($host, $user, $password, $database);

        if ($this->connect_error)

        {

            throw new Exception('Error connecting to MySQL : ' . $this->connect_errno . ' ' . $this->connect_error);

        }

   }

 

 

    // prevent cloning class instance

    private function __clone(){}

   

    // perform query

    public function runQuery($query)

    {

        if (is_string($query) AND !empty($query))

        {

            if ((!$this->real_query($query)))

            {

                throw new Exception('Error performing query ' . $query . ' - Error message : ' . $this->error);

            }

            return new MySQLi_ResultWrapper($this);

        }

    }

   

    // get insertion ID

    public function getInsertID()

    {

        return $this->insert_id;

    }

   

    // close database connection

    public function __destruct()

    {

        $this->close();

    }

}

Since at this point the inner workings of the previous “MySQLiWrapper” class should be pretty familiar to you, we'll move forward and take a close look at the definition of the following class. As I explained in the introduction, aside from implementing the Iterator and Countable PHP interfaces, this class includes two of the methods declared by ArrayAcess. Here’s how this other sample class has been defined:

class MySQLi_ResultWrapper extends MySQLi_Result implements Iterator, ArrayAccess, Countable

{

    private $_pointer = 0;

   

   // fetch row as an object

    public function fetchObject()

    {

        if (!$row = $this->fetch_object())

        {

            return NULL;

        }

        return $row;

    }

   

    // fetch row as an associative array

    public function fetchAssocArray()

    {

        if (!$row = $this->fetch_assoc())

        {

            return NULL;

        }

        return $row;

    }

   

    // fetch row as an enumerated array

    public function fetchNumArray()

    {

        if (!$row = $this->fetch_row())

        {

            return NULL;

        }

        return $row;

    }

   

    // fetch all rows

    public function fetchAll($type = MYSQLI_ASSOC)

    {

        if ($type !== MYSQLI_ASSOC AND $type !== MYSQLI_NUM AND $type !== MYSQLI_BOTH)

        {

            $type = MYSQLI_ASSOC;

        }

        if (!$rows = $this->fetch_all($type))

        {

            return NULL;

        }

        return $rows;  

    }

   

    // get definition information on fields

    public function fetchFieldsInfo()

    {

        if (!$fieldsInfo = $this->fetch_fields())

        {

            throw new Exception('No information available for table fields.');

        }

        return $fieldsInfo;

    }

   

    // get definition information on next field

    public function fetchFieldInfo()

    {

        if (!$fieldInfo = $this->fetch_field())

        {

            throw new Exception('No information available for current table field.');   

        }

        return $fieldInfo;

    }

   

    // move pointer in result set to specified offset

    public function movePointer($offset)

    {

        $offset = abs((int)$offset);

        $limit = $this->num_rows - 1;

        if ($limit <= 0 OR $offset > $limit)

        {

            return NULL;

        }

        unset($limit);

        return $this->data_seek($offset);

    }

   

    // count rows in result set (implementation required by 'count()' method in Countable interface)

    public function count()

    {

        return $this->num_rows;

    }

   

    // reset result set pointer (implementation required by 'rewind()' method in Iterator interface)

    public function rewind()

    {

        $this->_pointer = 0;

        $this->movePointer($this->_pointer);

        return $this; 

    }

   

    // get current row set in result set (implementation required by 'current()' method in Iterator interface)

    public function current()

    {

        if (!$this->valid())

        {

            throw new Exception('Unable to retrieve current row.');

        }

        $this->movePointer($this->_pointer);

        return $this->fetchObject();

    }

   

    // get current result set pointer (implementation required by 'key()' method in Iterator interface)

    public function key()

    {

        return $this->_pointer;

    }

   

    // move forward result set pointer (implementation required by 'next()' method in Iterator interface)

    public function next()

    {

        ++$this->_pointer;

        $this->movePointer($this->_pointer);

        return $this;

    }

   

    // determine if result set pointer is valid or not (implementation required by 'valid()' method in Iterator interface)

    public function valid()

    {

        return $this->_pointer < $this->num_rows;

    }

   

    // determine if the given offset exists (implementation required by 'offsetExists()' method in ArrayAccess interface)

    public function offsetExists($offset)

    {

        $this->movePointer($offset);

        $row = $this->fetchObject();

        return isset($row);

    }

   

    // not implemented (required by 'offsetSet()' method in ArrayAccess interface)

    public function offsetSet($offset, $value){}

   

    // free up result set

    public function __destruct()

    {

        $this->close();

    }

}

So far, there’s nothing hard to understand with reference to the way the “MySQLi_ResultWrapper” class has been defined, right? As I said before, this class is only a partial implementer of the ArrayAccess interface, as it defines two of the four methods of the interface, “offsetExists()” and “offsetSet()” respectively.

For obvious reasons, in its current state the class isn’t fully functional, since it must include all of the methods defined by ArrayAccess. Therefore, to suit this requirement, in the following section I’m going to add to the class another method of the corresponding interface, called “offsetUnset(),” which in this case won’t have any explicit implementation.

Now, click on the link below and read the next segment.



 
 
>>> More PHP Articles          >>> More By Alejandro Gervasio
 

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