点评：这个方法就是核心了，代码量不多，但是作用很明确，它会通过你提供的两个参数，自动生成相应的数据库连接类的对象。具有一定的灵活性，机动性。
主要是其中的
$adapterName = $adapterNamespace . '_';
$adapterName .= str_replace(' ', '_', ucwords(str_replace('_', ' ', strtolower($adapter))));
/*
* Load the adapter class. This throws an exception
* if the specified class cannot be loaded.
*/
if (!class_exists($adapterName)) {
require_once 'Zend/Loader.php';
Zend_Loader::loadClass($adapterName);
}
这段代码会引入相应的数据库连接类，比如前面的两个例子，就是分别引入了Zend目录下Db目录下Adapter目录下Pdo目录下的mysql.php类。
不同的数据库，会引入不同的数据库文件。
我们来看看mysql.php类中的内容：
<?php
/**
* Zend Framework
*
* LICENSE
*
* This source file is subject to the new BSD license that is bundled
* with this package in the file LICENSE.txt.
* It is also available through the world-wide-web at this URL:
* http://framework.zend.com/license/new-bsd
* If you did not receive a copy of the license and are unable to
* obtain it through the world-wide-web, please send an email
* to license@zend.com so we can send you a copy immediately.
*
* @category Zend
* @package Zend_Db
* @subpackage Adapter
* @copyright Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)
* @license http://framework.zend.com/license/new-bsd New BSD License
* @version $Id: Mysql.php 24593 2012-01-05 20:35:02Z matthew $
*/
/**
* @see Zend_Db_Adapter_Pdo_Abstract
*/
require_once 'Zend/Db/Adapter/Pdo/Abstract.php';
/**
* Class for connecting to MySQL databases and performing common operations.
*
* @category Zend
* @package Zend_Db
* @subpackage Adapter
* @copyright Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)
* @license http://framework.zend.com/license/new-bsd New BSD License
*/
class Zend_Db_Adapter_Pdo_Mysql extends Zend_Db_Adapter_Pdo_Abstract
{
/**
* PDO type.
*
* @var string
*/
protected $_pdoType = 'mysql';
/**
* Keys are UPPERCASE SQL datatypes or the constants
* Zend_Db::INT_TYPE, Zend_Db::BIGINT_TYPE, or Zend_Db::FLOAT_TYPE.
*
* Values are:
* 0 = 32-bit integer
* 1 = 64-bit integer
* 2 = float or decimal
*
* @var array Associative array of datatypes to values 0, 1, or 2.
*/
protected $_numericDataTypes = array(
Zend_Db::INT_TYPE => Zend_Db::INT_TYPE,
Zend_Db::BIGINT_TYPE => Zend_Db::BIGINT_TYPE,
Zend_Db::FLOAT_TYPE => Zend_Db::FLOAT_TYPE,
'INT' => Zend_Db::INT_TYPE,
'INTEGER' => Zend_Db::INT_TYPE,
'MEDIUMINT' => Zend_Db::INT_TYPE,
'SMALLINT' => Zend_Db::INT_TYPE,
'TINYINT' => Zend_Db::INT_TYPE,
'BIGINT' => Zend_Db::BIGINT_TYPE,
'SERIAL' => Zend_Db::BIGINT_TYPE,
'DEC' => Zend_Db::FLOAT_TYPE,
'DECIMAL' => Zend_Db::FLOAT_TYPE,
'DOUBLE' => Zend_Db::FLOAT_TYPE,
'DOUBLE PRECISION' => Zend_Db::FLOAT_TYPE,
'FIXED' => Zend_Db::FLOAT_TYPE,
'FLOAT' => Zend_Db::FLOAT_TYPE
);
/**
* Override _dsn() and ensure that charset is incorporated in mysql
* @see Zend_Db_Adapter_Pdo_Abstract::_dsn()
*/
protected function _dsn()
{
$dsn = parent::_dsn();
if (isset($this->_config['charset'])) {
$dsn .= ';charset=' . $this->_config['charset'];
}
return $dsn;
}
/**
* Creates a PDO object and connects to the database.
*
* @return void
* @throws Zend_Db_Adapter_Exception
*/
protected function _connect()
{
if ($this->_connection) {
return;
}
if (!empty($this->_config['charset'])) {
$initCommand = "SET NAMES '" . $this->_config['charset'] . "'";
$this->_config['driver_options'][1002] = $initCommand; // 1002 = PDO::MYSQL_ATTR_INIT_COMMAND
}
parent::_connect();
}
/**
* @return string
*/
public function getQuoteIdentifierSymbol()
{
return "`";
}
/**
* Returns a list of the tables in the database.
*
* @return array
*/
public function listTables()
{
return $this->fetchCol('SHOW TABLES');
}
/**
* Returns the column descriptions for a table.
*
* The return value is an associative array keyed by the column name,
* as returned by the RDBMS.
*
* The value of each array element is an associative array
* with the following keys:
*
* SCHEMA_NAME => string; name of database or schema
* TABLE_NAME => string;
* COLUMN_NAME => string; column name
* COLUMN_POSITION => number; ordinal position of column in table
* DATA_TYPE => string; SQL datatype name of column
* DEFAULT => string; default expression of column, null if none
* NULLABLE => boolean; true if column can have nulls
* LENGTH => number; length of CHAR/VARCHAR
* SCALE => number; scale of NUMERIC/DECIMAL
* PRECISION => number; precision of NUMERIC/DECIMAL
* UNSIGNED => boolean; unsigned property of an integer type
* PRIMARY => boolean; true if column is part of the primary key
* PRIMARY_POSITION => integer; position of column in primary key
* IDENTITY => integer; true if column is auto-generated with unique values
*
* @param string $tableName
* @param string $schemaName OPTIONAL
* @return array
*/
public function describeTable($tableName, $schemaName = null)
{
// @todo use INFORMATION_SCHEMA someday when MySQL's
// implementation has reasonably good performance and
// the version with this improvement is in wide use.
if ($schemaName) {
$sql = 'DESCRIBE ' . $this->quoteIdentifier("$schemaName.$tableName", true);
} else {
$sql = 'DESCRIBE ' . $this->quoteIdentifier($tableName, true);
}
$stmt = $this->query($sql);
// Use FETCH_NUM so we are not dependent on the CASE attribute of the PDO connection
$result = $stmt->fetchAll(Zend_Db::FETCH_NUM);
$field = 0;
$type = 1;
$null = 2;
$key = 3;
$default = 4;
$extra = 5;
$desc = array();
$i = 1;
$p = 1;
foreach ($result as $row) {
list($length, $scale, $precision, $unsigned, $primary, $primaryPosition, $identity)
= array(null, null, null, null, false, null, false);
if (preg_match('/unsigned/', $row[$type])) {
$unsigned = true;
}
if (preg_match('/^((?:var)?char)((d+))/', $row[$type], $matches)) {
$row[$type] = $matches[1];
$length = $matches[2];
} else if (preg_match('/^decimal((d+),(d+))/', $row[$type], $matches)) {
$row[$type] = 'decimal';
$precision = $matches[1];
$scale = $matches[2];
} else if (preg_match('/^float((d+),(d+))/', $row[$type], $matches)) {
$row[$type] = 'float';
$precision = $matches[1];
$scale = $matches[2];
} else if (preg_match('/^((?:big|medium|small|tiny)?int)((d+))/', $row[$type], $matches)) {
$row[$type] = $matches[1];
// The optional argument of a MySQL int type is not precision
// or length; it is only a hint for display width.
}
if (strtoupper($row[$key]) == 'PRI') {
$primary = true;
$primaryPosition = $p;
if ($row[$extra] == 'auto_increment') {
$identity = true;
} else {
$identity = false;
}
++$p;
}
$desc[$this->foldCase($row[$field])] = array(
'SCHEMA_NAME' => null, // @todo
'TABLE_NAME' => $this->foldCase($tableName),
'COLUMN_NAME' => $this->foldCase($row[$field]),
'COLUMN_POSITION' => $i,
'DATA_TYPE' => $row[$type],
'DEFAULT' => $row[$default],
'NULLABLE' => (bool) ($row[$null] == 'YES'),
'LENGTH' => $length,
'SCALE' => $scale,
'PRECISION' => $precision,
'UNSIGNED' => $unsigned,
'PRIMARY' => $primary,
'PRIMARY_POSITION' => $primaryPosition,
'IDENTITY' => $identity
);
++$i;
}
return $desc;
}
/**
* Adds an adapter-specific LIMIT clause to the SELECT statement.
*
* @param string $sql
* @param integer $count
* @param integer $offset OPTIONAL
* @throws Zend_Db_Adapter_Exception
* @return string
*/
public function limit($sql, $count, $offset = 0)
{
$count = intval($count);
if ($count <= 0) {
/** @see Zend_Db_Adapter_Exception */
require_once 'Zend/Db/Adapter/Exception.php';
throw new Zend_Db_Adapter_Exception("LIMIT argument count=$count is not valid");
}
$offset = intval($offset);
if ($offset < 0) {
/** @see Zend_Db_Adapter_Exception */
require_once 'Zend/Db/Adapter/Exception.php';
throw new Zend_Db_Adapter_Exception("LIMIT argument offset=$offset is not valid");
}
$sql .= " LIMIT $count";
if ($offset > 0) {
$sql .= " OFFSET $offset";
}
return $sql;
}
}
