(5) Object-oriented design principles 1---General outline and single responsibility principle

1. General outline:

1. The five principles of object-oriented: single responsibility principle, interface isolation principle, open-closed principle, replacement principle, and dependency inversion principle.

2. Single responsibility principle:

1. As far as a class is concerned, there is only one reason for its change: the single responsibility principle.

2． Single responsibility has two meanings:

a.  Avoid spreading the same responsibilities to different classes

b.  Avoid one class taking on too many responsibilities

3.  Reasons for following the single responsibility principle: Reduce coupling between classes, Improve class reusability.

Three. Factory pattern:

1. The factory pattern allows objects to be instantiated when code is executed. Able to 'produce' objects.

2. Example:

<?php /*
 * 单一职责原则
 */
interface Db_Adapter{
    /*
     * 数据库连接
     * @param $config数据库配置
     * @return resource
     */
    public function connect($config);
    /*
     * 执行数据库查询
     * @param string $query 数据库查询sql字符串
     * @param mixed $handld 连接对象
     * @return resource
     */
    public function query($query,$handle);
}

class Db_Adapter_Mysql implements Db_Adapter{
    private $_dbLink;
    /*
     * 数据库连接
     *
     * @param $config 数据库配置
     * @throws Db_Exception
     * @return resource
     */
    public function connect($config){
        if ($this->_dbLink =
            @mysql_connect($config->host.(empty($config->port) ? '' : ':'.$config->port),
                $config->user,$config->password,true)){
            if (@mysql_select_db($config->database,$this->_dbLink)){
                if ( $config->charset){
                    mysql_query("SET NAMES '{$config->charset}'",$this->_dbLink);
                }
                return $this->_dbLink;
            }
        }
        /*数据库异常*/
        throw new Db_Exception(@mysql_error($this->_dbLink)); //这一句报了很多错
    }

    /*
     * 执行数据库查询
     *
     * @param string $query 数据库查询sql字符串
     * @param mixed $handle 连接对象
     * @return resource
     */
    public function query($query,$handle){
        $resource = "";
        if ($resource == @mysql_query($query,$handle)){
            return $resource;
        }
    }
}

class Db_Adapter_sqlite implements  Db_Adapter{
    private $_dbLink; //数据库连接字段标记
    /*
     * 数据库连接函数
     *
     * @param $config数据库配置
     * @throws DB_exception
     * @return resource
     */
    public function connect($config){
        if ($this->_dbLink = @mysql_connect($config->host.
            (empty($config->port) ? '' : ':'.$config->port),
            $config->user,$config->password,true)){
            if (@mysql_select_db($config->database,
                $this->_dbLink)){
                if ($config->charset){
                    mysql_query("SET NAMES '{$config->charset}'",$this->_dbLink);
                }
                return $this->_dbLink;
            }
        }
        /*数据库异常*/
        throw new Db_exception(@mysql_error($this->dbLink));
    }

    /*
     * 执行数据库查询
     *
     * @param string $query 数据库查询sql字符串
     * @param mixed $handle 连接对象
     * @return resource
     */
    public function query($query,$handle){
        $resource = "";
        if ($resource == @mysql_query($query,$handle)){
            return $resource;
        }
    }
}

$testDb = new Db_Adapter_Mysql();
$config = array(
    //这里写数据库配置
    'host'=>'localhost',
);

$testDb->connect($config);
$testDb->query($sql,$handle);

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