Call constructors in various ways to create PDO objects

Call the constructor in a variety of ways to create a PDO object

The constructor can be called in a variety of ways to create a PDO object. The following is to connect MySQL and Oracle. Taking the server as an example, we will introduce the various calling methods of the construction method.

1. Embed parameters into the constructor

In the following example of connecting to the Oracle server, load the OCI driver in the DSN string The program also specifies two optional parameters: the first is the database name, and the second is the character set. Use a specific character set to connect to a specific database. If no information is specified, the default database will be used. The code is as follows:

<?php
try{
    $dbh = new PDO("OCI:dbname = accounts;charset=UTF8","scott","tiger");
}catch (PDOException $e){
    echo "数据库连接失败：".$e->getMessage();
}
?>

OCI:dbname=accounts tells PDO that it should use the OCI driver, and that the "accounts" database should be used. For the MySQL driver, everything after the first colon will be used as the MySQL DSN. The display when connecting to the MySQL server is as follows:

<?php
$dbms = "mysql";                                  // 数据库的类型
$dbName ="php_cn";                                //使用的数据库名称
$user = "root";                                   //使用的数据库用户名
$pwd = "root";                                    //使用的数据库密码
$host = "localhost";                              //使用的主机名称
$dsn  = "$dbms:host=$host;dbname=$dbName";
try {
    $pdo = new PDO($dsn, $user, $pwd);//初始化一个PDO对象，就是创建了数据库连接对象$pdo
}catch (PDOException $e){
   echo "数据库连接失败：".$e->getMessage();
}
?>

Other drivers will also parse its DSN in different ways. If the driver cannot be loaded, or a connection failure occurs, a PDOException will be thrown so that you can You can decide how best to handle the failure. Omitting the try...catch control structure has no benefit; if exception handling is not defined at a higher level in the application, the script will terminate if the database connection cannot be established.

2. Store the parameters in the file

When creating a PDO object, you can put the DSN string in another local or remote location file, and reference this file in the constructor, as shown below:

<?php
try{
    $dbh = new PDO(&#39;uri:file:///usr/localhost/dbconnect&#39;,&#39;webuser&#39;,&#39;password&#39;);
}catch(PDOException $e){
    echo &#39;连接失败：&#39;.$e->getMessage();
}
?>

As long as the DSN driver in the file /usr/localhost/dbconnect is changed, you can switch between multiple database systems, but Make sure that the file is owned by the user responsible for executing the PHP script and that this user has the necessary permissions.

3. Reference the php.ini file

You can also maintain DSN information in the configuration file of the PHP server, as long as it is in the php.ini file Zhongba DSN information is passed to a configuration parameter named pdo.dsn.aliasname, where aliasname is the DSN alias that will be provided to the constructor later. Connect to the Oracle server as shown below. The alias specified for the DSN in php.ini is oraclepdo:

【PDO】
pdo.dsn.oraclepdo = “OCI:dbname=//localhost：1521/mydb；chaset=UTF-8”；

After restarting the Apaceh server, you can call the PDO construction method in the first PDO constructor in the PHP program. Use this alias in the parameters, as follows:

<?php
try{
    $dbh = new PDO(&#39;oraclepdo&#39;,&#39;scott&#39;,&#39;tiger&#39;);//使用php.ini文件中的oraclepdo 别名
}catch(PDOException $e){
    echo &#39;连接失败：&#39;.$e->getMessage();
}
?>

4. PDO connection-related options

When creating a PDO object, there are For some options related to database connection, you can pass the necessary options into an array to the fourth parameter driver_opts of the constructor to pass additional tuning parameters to PDO or the underlying driver. Some common usage options are as shown in the table:

选项名	描述
PDO::ATTR_AUTOCOMMIT	确定PDO是否关闭自定提交功能，设置FALSE值时关闭
PDO::ATTR_CASE	强制PDO获取的表字段字符的大小转换，或远原样使用列信息
PDO::ATTR_ERRMODE	设置错误处理的模式
PDO::ATTR_PERSISTENT	确定连接是否为持久连接，默认值为FALSE
PDO::ATTR_ORACCLE_NULLS	将返回的空字符串转换为SQL的NULL
PDO::ATTR_PREFETCH	设置应用程序提前获取的数据大小，以K字节单位
PDO::ATTR_TIMEOUT	设置超市之前等待的时间（秒数）
PDO::ATTR_SERVER_INFO	包含与数据库特有的服务器信息
PDO::ATTR_SERVER_VERSION	包含与数据库服务器版本号有关的信息
PDO::ATTR_CLIENT_VERSION	包含与数据库客户端版本号有关的信息
PDO::ATTR_CONNECTION_STATUS	包含数据库特有的与连接状态有关的信息

设置选项名为下表组成的关联数组，作为驱动程序特定的连接选项，传递给PDO构造方法的第四各参数中，在下面的实例中使用连接选项创建持久连接，持久连接的好处是能够避免在每个页面执行到打开和关闭数据库服务器连接，速度更快，如 MySQL数据库的一个进程创建了两个连接，PHP则会把原有连接与新的连接合并共享为一个连接，代码如下：

<?php
$opt = array(PDO::ATTR_PERSISTENT =>true);
try{
    $dbh = new PDO(&#39;mysql:host=localhost;dbname=test&#39;,&#39;dbuser&#39;,&#39;password&#39;,$opt); //使用$opt参数
}catch(PDOException $e){
    echo &#39;连接失败：&#39;.$e->getMessage();
}
?>

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