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Adding an offsetSet() method - PHP

In this fourth part of a six-part series, that covers the Iterator, Countable, and ArrayAccess SPL interfaces, I show how to partially implement the methods declared by the ArrayAccess SPL interface within a sample class that manipulates MySQL result sets.

TABLE OF CONTENTS:
  1. Using the ArrayAccess SPL Interface
  2. Review: implementing the Iterator and Countable SPL interfaces
  3. Implementing the ArrayAccess SPL interface's offsetExists() method
  4. Adding an offsetSet() method
By: Alejandro Gervasio
Rating: starstarstarstarstar / 1
April 06, 2010

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The last topic that I plan to cover in this tutorial will be the inclusion of an "offsetSet()" method within the "MySQLi_ResultWrapper" class. As you'll recall, this method is one of the four declared by the ArrayAccess interface, so this process is mandatory. In accordance with this, now the source code of the pertinent class will look like this:  

 

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();

    }

}

Done. At this point, the "MySQLi_ResultWrapper" class defines two methods of the ArrayAccess interface, even though only one of them has a concrete implementation. Again, at the risk of being repetitive, if you test the class in its current version, you'll get an error from the PHP interpreter. Please be patient for now, as the remaining interface methods will be added to the class in the course of the next article. Meanwhile, feel free to edit all of the code samples shown in this tutorial, which will sharpen your skills when implementing the Iterator, Countable and ArrayAccess PHP 5 interfaces.

Final thoughts

That's all for now. In this part of the series, I showed how to partially implement the methods declared by the ArrayAccess SPL interface within a sample class that manipulates MySQL result sets. At this point, the class only defines two of the four methods required by the interface, but it's mandatory to give a definition to the remaining ones. This issue will be properly addressed in the next part of the series, so you can't miss it!



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

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