問(wèn)題描述

我是不是瘋了，還是 Postgres PDO 驅(qū)動(dòng)程序不支持準(zhǔn)備好的語(yǔ)句，而是在客戶端模擬它們?

Am I losing my mind, or does the Postgres PDO driver just not support prepared statements, but instead emulates them client side?

以下代碼為 prepare() 調(diào)用返回 NO ERROR，即使它應(yīng)該.相反，它在調(diào)用 execute() 時(shí)返回適用的錯(cuò)誤.

The following code returns NO ERROR for the prepare() call, even though it should. Instead, it returns the applicable error when execute() is called.

因?yàn)楦鶕?jù) Daniel Vérité 我錯(cuò)了，我添加了他建議的代碼.我仍然收到錯(cuò)誤.我的代碼現(xiàn)在看起來(lái)像下面這樣，添加了 Daniel 的行.

Since according to Daniel Vérité I'm wrong, I added his suggested code. I still get the error. My code now looks like the below, with Daniel's line added.

<?php
$pdo = new PDO("pgsql:host=myhost;dbname=mydatabase");

$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);  // as suggested by Daniel

$sth = $pdo->prepare('COMPLETE GARBAGE');
echo "[prepare] errorInfo = " . print_r($sth->errorInfo(), true);

$sth->execute();
echo "[execute] errorInfo = " . print_r($sth->errorInfo(), true);

PHP 5.3.15 版，PHP Postgres 客戶端 9.1.4 版，Postgres 服務(wù)器版 9.2.1.

PHP version 5.3.15, PHP Postgres client version 9.1.4, Postgres server version 9.2.1.

推薦答案

參見 http://www.php.net/manual/en/pdo.prepare.php

注意:

模擬的預(yù)處理語(yǔ)句不與數(shù)據(jù)庫(kù)通信服務(wù)器，因此 PDO::prepare() 不檢查語(yǔ)句.

Emulated prepared statements does not communicate with the database server so PDO::prepare() does not check the statement.

(實(shí)際上，無(wú)論如何都不會(huì)立即發(fā)送真正的準(zhǔn)備好的語(yǔ)句，請(qǐng)參閱下面對(duì) Q2 的回答)

(in fact real prepared statements are not sent immediately anyway, see answer to Q2 below)

無(wú)論如何你可以發(fā)出:

$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES,false); 

獲得使用 SQL PREPARE 命令實(shí)現(xiàn)的真正準(zhǔn)備好的語(yǔ)句.請(qǐng)參閱http://www.php.net/manual/en/pdo.setattribute.php了解更多.

to get real prepared statements implemented with the SQL PREPARE command. See http://www.php.net/manual/en/pdo.setattribute.php for more.

在進(jìn)一步的討論和測(cè)試中，出現(xiàn)了兩個(gè)問(wèn)題:

On further discussion and tests, two questions arise:

第一季度.為什么 pdo::getAttribute(PDO::ATTR_EMULATE_PREPARES) 會(huì)產(chǎn)生錯(cuò)誤?
實(shí)際上 setAttribute 沒(méi)有出錯(cuò)，但是 getAttribute(PDO::ATTR_EMULATE_PREPARES) 說(shuō):

Q1. Why does pdo::getAttribute(PDO::ATTR_EMULATE_PREPARES) yield an error?
Indeed setAttribute doesn't error out but getAttribute(PDO::ATTR_EMULATE_PREPARES) says:

'SQLSTATE[IM001]: 驅(qū)動(dòng)程序不支持此功能:驅(qū)動(dòng)程序支持不支持該屬性'

'SQLSTATE[IM001]: Driver does not support this function: driver does not support that attribute'

查看 pdo::getAttribute 的文檔，它說(shuō)常量適用于數(shù)據(jù)庫(kù)連接的如下，從PDO::ATTR_AUTOCOMMIT到PDO::ATTR_TIMEOUT的一些常量，值得注意的是PDO::ATTR_EMULATE_PREPARES 不在其中.所以嚴(yán)格來(lái)說(shuō)，無(wú)論如何，我們不應(yīng)該期望 getAttribute(PDO::ATTR_EMULATE_PREPARES) 起作用.

Looking at the documentation for pdo::getAttribute, it says The constants that apply to database connections are as follows, and a number of constants follow from PDO::ATTR_AUTOCOMMIT to PDO::ATTR_TIMEOUT, and it's remarkable that PDO::ATTR_EMULATE_PREPARES is not in them. So strictly speaking, we should not expect getAttribute(PDO::ATTR_EMULATE_PREPARES) to work, anyway.

現(xiàn)在查看源代碼可以肯定的是，pdo_pgsql 驅(qū)動(dòng)程序似乎提供了一個(gè) pdo_pgsql_get_attribute 函數(shù)，該函數(shù)具有一個(gè) switch 語(yǔ)句:

Now looking at the source code to be sure, it appears that the pdo_pgsql driver provides a pdo_pgsql_get_attribute function that has a switch statement on:

• PDO_ATTR_CLIENT_VERSION
• PDO_ATTR_SERVER_VERSION
• PDO_ATTR_CONNECTION_STATUS
• PDO_ATTR_SERVER_INFO

就是這樣.沒(méi)有 PDO_ATTR_EMULATE_PREPARES 的痕跡，這就是最終出現(xiàn)此錯(cuò)誤的原因.

and that's it. No trace of PDO_ATTR_EMULATE_PREPARES which is why ultimately this error appears.

另一方面，函數(shù)pdo_pgsql_set_attr有一個(gè)switch語(yǔ)句:

On the other hand, the function pdo_pgsql_set_attr has a switch statement on:

• PDO_ATTR_EMULATE_PREPARES
• PDO_PGSQL_ATTR_DISABLE_NATIVE_PREPARED_STATEMENT

確認(rèn)在設(shè)置時(shí)實(shí)際考慮了此屬性.所以 PDO 只是與 getAttribute 不一致，不匹配 setAttribute.

which confirms that this attribute is actually taken into account when set. So PDO is just inconsistent with getAttribute that doesn't match setAttribute.

Q2 - 當(dāng)準(zhǔn)備模擬為假時(shí)，為什么虛假語(yǔ)句在準(zhǔn)備時(shí)不會(huì)立即引發(fā)錯(cuò)誤?

考慮pgsql_statement.c中的這段代碼:

        if (!S->is_prepared) {
stmt_retry:
            /* we deferred the prepare until now, because we didn't
             * know anything about the parameter types; now we do */
            S->result = PQprepare(H->server, S->stmt_name, S->query, 
                        stmt->bound_params ? zend_hash_num_elements(stmt->bound_params) : 0,
                        S->param_types);

它表明使用了 PQprepare(所以這是一個(gè)真正的"準(zhǔn)備好的語(yǔ)句)，而且該語(yǔ)句不會(huì)立即發(fā)送到服務(wù)器.這就是 dbo::prepare("bogus statement") 不會(huì)返回 false 的原因:它實(shí)際上不會(huì)因?yàn)槿鄙賲?shù)類型而發(fā)送到服務(wù)器.

It shows that PQprepare is used (so that's a "real" prepared statement), but also that the statement is not immediately sent to the server. That's why the dbo::prepare("bogus statement") won't return false: it's actually not sent to the server for lack of parameter types.

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