Using PHP reflection mechanism to construct sql statement of 'CREATE TABLE'

Reflection refers to the extended analysis of PHP programs in the running state of PHP, and derives or extracts detailed information about classes, methods, attributes, parameters, etc., including comments. This dynamically retrieved information and the ability to call methods of objects dynamically is called Reflection API. Reflection is an API that manipulates the metamodel in the object-oriented paradigm and is powerful enough to help us build complex, extensible applications.

Its applications include auto-loading plug-ins, auto-generation of documents, and even extensions to the PHP language.

php Reflection api consists of several classes that help us access metadata for a program or interact with related annotations. With reflection, we can get methods such as those implemented by the class, create an instance of the class (different from those created with new), call a method (also different from regular calls), pass parameters, and dynamically call static methods of the class.

Reflective api is an oop technology extension built into php that includes a class, exception, and interface that can be combined to help us analyze other classes, interfaces, methods, properties, methods, and extensions. These oop extensions are called reflections.

The following program uses Reflection to construct the sql statement of "CREATE TABLE". If you are not familiar with the reflection mechanism, you can see the charm and function of reflection from this program.

<?php
/**
 * Creates an SQL 'Create Table' based upon an entity
 * @author Chris Tankersley <chris@ctankersley.com>
 * @copyright 2010 Chris Tankersley
 * @package PhpORM_Cli
 */
class PhpORM_Cli_GenerateSql
{
  /**
   * Use a MySQL database
   */
  const MYSQL = 'mysql';
  /**
   * Use a SQLite database
   */
  const SQLITE = 'sqlite';
  /**
   * Types that are allowed to have a length
   * @var array
   */
  protected $_hasLength = array('integer', 'varchar');
  /**
   * Regexes needed to pull out the different comments
   * @var array
   */
  protected $_regexes = array(
    'type' => '/ type=([a-z_]*) /',
    'length' => '/ length=([0-9]*) /',
    'default' => '/ default="(.*)" /',
    'null' => '/ null /',
  );
  /**
   * Types that we support
   * @var array
   */
  protected $_validTypes = array(
    'boolean' => 'BOOL',
    'date' => 'DATE',
    'integer' => 'INT',
    'primary_autoincrement' => 'INT AUTO_INCREMENT PRIMARY KEY',
    'text' => 'TEXT',
    'timestamp' => 'TIMESTAMP',
    'varchar' => 'VARCHAR',
  );
  /**
   * Name of the class we will interperet
   * @var string
   */
  protected $_className;
  /**
   * Name of the table we are generating
   * @var string
   */
  protected $_tableName;
  /**
   * The type of database we are generating
   * @var string
   */
  protected $_type;
  /**
   * Sets the name of the class we are working with
   * @param string $class
   * @param string $table_name
   * @param string $type
   */
  public function __construct($class, $table_name, $type = self::MYSQL)
  {
    $this->_className = $class;
    $this->_tableName = $table_name;
    $this->_type = $type;
  }
  /**
   * Builds an SQL Line for a property
   * @param ReflectionProperty $property
   * @return string
   */
  protected function _getDefinition($property)
  {
    $type = '';
    $length = '';
    $null = '';
    preg_match($this->_regexes['type'], $property->getDocComment(), $matches);
    if(count($matches) == 2) {
      if(array_key_exists($matches[1], $this->_validTypes)) {
        $type = $this->_validTypes[$matches[1]];
        if(in_array($matches[1], $this->_hasLength)) {
          $length = $this->_getLength($property);
        }
        if($matches[1] != 'primary_autoincrement') {
          $null = $this->_getNull($property);
        }
        $sql = '`'.$property->getName().'` '.$type.' '.$length.' '.$null;
        return $sql;
      } else {
        throw new Exception('Type "'.$matches[1].'" is not a supported SQL type');
      }
    } else {
      throw new Exception('Found '.count($matches).' when checking Type for property '.$property->getName());
    }
  }
  /**
   * Extracts the Length from a property
   * @param ReflectionProperty $property
   * @return string
   */
  protected function _getLength($property)
  {
    preg_match($this->_regexes['length'], $property->getDocComment(), $matches);
    if(count($matches) == 2) {
      return '('.$matches[1].')';
    } else {
      return '';
    }
  }
  /**
   * Determines if a Property is allowed to be null
   * @param ReflectionProperty $property
   * @return string
   */
  protected function _getNull($property)
  {
    preg_match($this->_regexes['null'], $property->getDocComment(), $matches);
    if(count($matches) == 1) {
      return 'NULL';
    } else {
      return 'NOT NULL';
    }
  }
  /**
   * Generates a block of SQL to create a table from an Entity
   * @return string
   */
  public function getSql()
  {
    $class = new ReflectionClass($this->_className);
    $definitions = array();
    foreach($class->getProperties() as $property) {
      if(strpos($property->getName(), '_') === false) {
        $definitions[] = $this->_getDefinition($property);
      }
    }
    $columns = implode(",n", $definitions);
    $sql = "CREATE TABLE ".$this->_tableName." (".$columns.")";
    if($this->_type == self::MYSQL) {
      $sql .= " ENGINE=MYISAM";
    }
    return $sql.";";
  }
}

Summarize