yii源码三 -- db

《AR》

CActiveRecord：
path:/framework/db/ar/CActiveRecord.php
overview:is the base class for classes representing relational data.It implements the active record design pattern, a popular Object-Relational Mapping (ORM) technique.

实现原理：首先一套__sleep(),__get(),__set(),__isset(),__unset(),__call()魔术方法，来处理model和model属性。

public function getRelated($name,$refresh=false,$params=array()){}
　　对该方法，有一段很重要的介绍如下：

* Returns the related record(s).
* This method will return the related record(s) of the current record.
* If the relation is HAS_ONE or BELONGS_TO, it will return a single object
* or null if the object does not exist.
* If the relation is HAS_MANY or MANY_MANY, it will return an array of objects
* or an empty array.

public function primaryKey(){}
　　如何表设置了主键，则返回null，不需要覆盖该方法；否则返回array()，且需要覆盖该方法。

《schema》

CDbConnection:
path:/framework/db/CDbConnection.php
overview:CDbConnection represents a connection to a database.

工作原理：CDbConnection works together with CDbCommand, CDbDataReader and CDbTransaction to provide data access to various DBMS。且基于PDO扩展。

　　首先用$connection = new CDbConnection($dsn,$username,$password)创建一个连接实例，然后调用$connection->active=true启动连接。

用法：
1.创建DB实例并建立连接：

$connection=new CDbConnection($dsn,$username,$password);
$connection->active=true; //建立连接

2.执行sql语句:

$command=$connection->createCommand($sqlStatement);
$command->execute();   //执行非查询语句(insert,delete,update)
$reader=$command->query();//执行查询语句(select)

备注：预处理和绑定参数用法：

$command=$connection->createCommand($sqlStatement);
$command->bindParam($name1,$value1);
$command->bindParam($name2,$value2);
$command->execute();

3.获取结果：

foreach($reader as $row){
      ......
}

4.事务：

$transaction=$connection->beginTransaction();
try{
    $connection->createCommand($sql1)->execute();
    $connection->createCommand($sql2)->execute();
    //.... other SQL executions
    $transaction->commit();
}catch(Exception $e){
    $transaction->rollback();
 }

5.由于CDbConnection实现了IApplicationComponent接口，所以它可以当作一个application component并且在application配置文件(main.php)里配置数据库连接信息：

array(
     'components'=>array(
         'db'=>array(
              'class'=>'CDbConnection',
              'connectionString'=>'sqlite:path/to/dbfile',
         ),
     ),
)

CDbCommandBuilder：
path:/framework/db/schema/CDbCommandBuilder.php
overview:provides basic methods to create query commands for tables.

CDbDataReader:
path:/framework/db/schema/CDbDataReader.php
overview:represents a forward-only stream of rows from a query result set.

CDbTransaction:
path:/framework/db/schema/CDbTransaction.php
overview:a DB transaction.

$transaction=$connection->beginTransaction();
try{
    $connection->createCommand($sql1)->execute();
    $connection->createCommand($sql2)->execute();
    //.... other SQL executions
    $transaction->commit();
}
catch(Exception $e){
    $transaction->rollback();
}

...