PDOStatement::setFetchMode()

(PHP 5 >= 5.1.0, PHP 7, PECL pdo >= 0.2.0)

为语句设置默认的获取模式。

说明

参数

获取模式必须是PDO::FETCH_*系列常量中的一个。

列号。

类名。

构造函数参数。

对象。

返回值

成功时返回TRUE，或者在失败时返回FALSE。

范例

设置获取模式

The following example demonstrates how PDOStatement::setFetchMode() changes the default fetch mode for a PDOStatement object.下面的例子示范如何用PDOStatement::setFetchMode()来为一个 PDOStatement 对象更改默认的获取模式。

以上例程会输出：

apple   red     150
banana  yellow  250
orange  orange  300
kiwi    brown   75
lemon   yellow  25
pear    green   150
watermelon      pink    90

if you want to fetch your result into a class (by using PDO::FETCH_CLASS) and want the constructor to be executed *before* PDO assings the object properties, you need to use the PDO::FETCH_PROPS_LATE constant: 

Something very helpful is knowing how to access namespaces from the function. It took me a minute (and Google) to figure out. The ::class property is going to be your best friend in this case. 

Some note on PDO :: FETCH_CLASS | PDO :: FETCH_CLASSTYPE
It took me some time, to realize, that you can not use this fetch-mode in $stm->setFetchMode(), when you want to retrieve objects from the database whereas the type is defined by the first column in the resultset.
You have to define this mode directly in the $stm->fetch() method.
To make it clearer:
$stm = $pdo->query("SELECT * FROM `foo`);
$stm->setFetchMode(FETCH_CLASS | PDO :: FETCH_CLASSTYPE);
$object = $stm->fetch();
Will not return the expected object, whereas
$stm = $pdo->query("SELECT * FROM `foo`");
$object = $stm->fetch(FETCH_CLASS | PDO :: FETCH_CLASSTYPE);
will give you the object of the class, defined in the first column of `foo`.

To fetch the rows into an existing instance of a class, use PDO::FETCH_INTO and pass the object as the second parameter. 
The class _must_ have the column names declared as public members, or the script will die. But overloading with __set() and __get() lets it handle any column your query throws at it. 
Set the fetch mode right after you call prepare(). It appears you _must_ use execute() - fetch() won't work. A small example, adapted from ext/pdo/tests/pdo_025.phpt: 

PDO::FETCH_CLASS may be used only with this method and it takes up to three parameters then:
 - int mode
 - string className
 - array constructorArgs (optional)

Note also that the constructor is called AFTER the data is set on the object.

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