PDOStatement::getColumnMeta()

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

返回结果集中一列的元数据

说明

PDOStatement::getColumnMeta(int $column): array

Warning

此函数是实验性的。此函数的表象，包括名称及其相关文档都可能在未来的PHP 发布版本中未通知就被修改。使用本函数风险自担。

检索一个在结果集中以0开始索引的列的元数据作为一个关联数组。

Warning

并非所有 PDO 驱动都支持PDOStatement::getColumnMeta()。

参数

$column

结果集中以0开始索引的列。

返回值

返回一个关联数组，它包含了下列表示一个单独列的元数据的值：

如果结果集不存在，或者是请求的列在结果集中不存在，则返回FALSE。

更新日志

范例

检索列的元数据

下面例子展示了在一个PDO_SQLITE中，检索一个通过函数（COUNT）生成单独列的元数据的结果。

<?php
$select = $DB->query('SELECT COUNT(*) FROM fruit');
$meta = $select->getColumnMeta(0);
var_dump($meta);
?>

以上例程会输出：

array(6) {
  ["native_type"]=>
  string(7) "integer"
  ["flags"]=>
  array(0) {
  }
  ["name"]=>
  string(8) "COUNT(*)"
  ["len"]=>
  int(-1)
  ["precision"]=>
  int(0)
  ["pdo_type"]=>
  int(2)
}

参见

• PDOStatement::columnCount() 返回结果集中的列数
• PDOStatement::rowCount() 返回受上一个 SQL 语句影响的行数

This method is supported in the MySQL 5.0+ driver. It can be used for object hydration:
<?php
$pdo_stmt = $dbh->execute('SELECT discussion.id, discussion.text, comment.id, comment.text FROM discussions LEFT JOIN comments ON comment.discussion_id = discussion.id');
foreach(range(0, $pdo_stmt->columnCount() - 1) as $column_index)
{
 $meta[] = $pdo_stmt->getColumnMeta($column_index);
}
while($row = $pdo_stmt->fetch(PDO::FETCH_NUM))
{
 foreach($row as $column_index => $column_value)
 {
  //do something with the data, using the ids to establish the discussion.has_many(comments) relationship.
 }
}
?>
If you are building an ORM, this method is very useful to support more natural SQL syntax. Most ORMs require the column names to be aliases so that they can be parsed and turned into objects that properly represent has_one, has_many, many_to_many relationships.

I found a short discussion related to this function at 
http://www.sitepoint.com/forums/showthread.php?t=497257
I haven't tried it (yet?) but hopefully someone can find it useful.

native_type has the following mapping for MySQL:
(tested in PHP 5.4, MySQL 5.7)
INT(11) (PKs) => LONG
TINYINT(4)  => TINY
DOUBLE    => DOUBLE
VARCHAR    => VAR_STRING
CHAR     => STRING
DATE     => DATE
Functions   => VAR_STRING
- DATEFORMAT()
- CONCAT()

I recently added a note to a small function that went through the results of PDOStatement::fetch and mapped columns to integer or float types.
I forgot to test for columns that can have a null value!
I'm updating the code here, sorry.
This website doesn't let me edit the original comment, so I'm just gonna link to a gist in case it needs even further fixes.
https://gist.github.com/AeonFr/db3b2a8a95753076d9e4da42d29365d2
I basically added this code:
<?php
if ($value === null) {
  continue;
}
?>

I was able to successfully pull off basic type conversion for integer and float values in PDO.
NULL values were returning as null, but integers and floats weren't, so I decided to go with a simple solution.
It's not tested on all database types, so if you think it needs improvement, let me know (my twitter is "francanobr")
<?php
// Returns the contents of $stm (PDO Statement)
// as an associative array, with correct native types
// for integers, nulls, and floats
$array = [];
while ($fila = $stm->fetch(\PDO::FETCH_ASSOC)) {
  $i = 0;
  foreach ($fila as $key => $value) {
    $columnMeta = $stm->getColumnMeta($i);
    switch ($columnMeta['native_type']) {
      case 'LONG':
      case 'TINY':
        $fila[$key] = intval($value);
        break;
      case 'DOUBLE':
        $fila[$key] = floatval($value);
        break;
    }
    $i++;
  }
  $array[] = $fila;
}
return $array;
?>
The code sample is part of a function, the function declaration is not included, evaluate how to integrate it with your app.