pg_last_error()

(PHP 4 >= 4.2.0, PHP 5, PHP 7)

得到某连接的最后一条错误信息

说明

pg_last_error([resource $connection]): string

pg_last_error()返回指定连接$connection的最后一条错误信息。

错误信息可能会被 PostgreSQL(libpq)的内部函数调用所覆盖。如果 PostgreSQL 的内部模块函数产生了多个错误，则可能不能返回适当的错误信息。

使用pg_result_error()，pg_result_status()和pg_connection_status()来取得更好的错误处理。

Note:

本函数以前的名字为pg_errormessage()。

参见pg_result_error()。

From a practical view there are two types of error messages when using transactions:
-"Normal" errors: in this case, the application should stop the current process and show an error message to the user.
-Deadlock errors. This shows that the deadlock detection process of PostgreSQL found a circle of dependency, and broke it by rolling back the transaction in one of the processes, which gets this error msg. In this case, the application should not stop, but repeat the transaction.
I found no discrete way to find out which case are we dealing with. This interface doesn't support error codes, so we have to search for patterns in the message text.
Here is an example for PostgreSQL database connection class. It throws a PostgresException on "normal" errors, and DependencyException in the case of a broken deadlock, when we have to repeat the transaction.
postgres.php:
<?php
class PostgresException extends Exception {
  function __construct($msg) { parent::__construct($msg); }
}
class DependencyException extends PostgresException {
  function __construct() { parent::__construct("deadlock"); }
}
class pg {
  public static $connection;
  
  private static function connect() {
    self::$connection = @pg_connect("dbname=foodb user=foouser password=foopasswd");
    if (self::$connection === FALSE) {
      throw(new PostgresException("Can't connect to database server."));
    }
  }
  
  public static function query($sql) {
    if (!isset(self::$connection)) {
      self::connect();
    }
    
    $result = @pg_query(self::$connection, $sql);
    if ($result === FALSE) {
      $error = pg_last_error(self::$connection);
      if (stripos($error, "deadlock detected") !== false) throw(new DependencyException());
      
      throw(new PostgresException($error.": ".$sql));
    }
    
    $out = array();
    while ( ($d = pg_fetch_assoc($result)) !== FALSE) {
      $out[] = $d;
    }
    
    return $out;
  }
}
?>
It should be used in this way:
test.php:
<?php
include("postgres.php");
do {
  $repeat = false;
  try {
    pg::query("begin");
    
    ...
    $result = pg::query("SELECT * FROM public.kitten");
    ...
    pg::query("commit");
  }
  catch (DependencyException $e) {
    pg::query("rollback");
    $repeat = true;
  }
} while ($repeat);
?>
The normal errors should be caught at the frontend.
Tamas