问题描述

我看到的所有使用 mysqli_fetch_object 的示例都使用 mysql_query()，我无法让它与准备好的语句一起工作.有谁知道这段代码有什么问题，因为 fetch_object 返回 null.

All the examples I see using mysqli_fetch_object use mysql_query(), I cannot get it to work with prepared statements. Does anyone know what is wrong with this code snippet, as fetch_object returns null.

$sql = "select 1 from dual";
printf("preparing %s
", $sql);
$stmt = $link->prepare($sql);
printf("prepare statement %s
", is_null($stmt) ? "is null" : "created");
$rc = $stmt->execute();
printf("num rows is %d
", $stmt->num_rows);
$result = $stmt->result_metadata();
printf("result_metadata %s
", is_null($result) ? "is null" : "exists");
$rc = $result->fetch_object();
printf("fetch object returns %s
", is_null($rc) ? "NULL" : $rc);
$stmt->close();

输出为:

preparing select 1 from dual
prepare statement created
num rows is 0
result_metadata exists
fetch object returns NULL

推荐答案

我不相信界面是这样工作的.

I don't believe the interface works like that.

通过文档和示例(http://www.php.net/manual/en/mysqli.prepare.php) 似乎 $stmt->execute() 不返回结果集，而是一个指示成功/失败的布尔值(http://www.php.net/manual/en/mysqli-stmt.execute.php).要实际获得结果，您需要使用 $stmt->bind_result (http://www.php.net/manual/en/mysqli-stmt.bind-result.php).

Going by the documentation and examples (http://www.php.net/manual/en/mysqli.prepare.php) it seems that $stmt->execute() does not return a resultset, but a boolean indicating success / failure (http://www.php.net/manual/en/mysqli-stmt.execute.php). To actually get the result, you need to bind variables to the resultset (aftere the execute call) using $stmt->bind_result (http://www.php.net/manual/en/mysqli-stmt.bind-result.php).

完成所有这些之后，您可以重复调用 $stmt->fetch() () 以使用当前行中的列值填充绑定变量.我没有看到任何提及 $stmt->fetch_object() 的内容，也没有看到该接口如何与描述的变量绑定方案一起工作.

After you did all that, you can do repeated calls to $stmt->fetch() () to fill the bound variables with the column values from the current row. I don't see any mention of $stmt->fetch_object() nor do I see how that interface could work with a variable binding scheme like described.

这就是从 mysqli 准备好的语句中获取正常"结果的故事.

So this is the story for "normal" result fetching from mysqli prepared statments.

在您的代码中，我怀疑存在错误，或者至少我不确定您是否打算这样做.你行:

In your code, there is something that I suspect is an error, or at least I am not sure you intended to do this. You line:

$result = $stmt->result_metadata();

将结果集元数据(本身表示为结果集)分配给 $result 变量.根据文档 (http://www.php.net/manual/en/mysqli-stmt.result-metadata.php) 您只能在这些特殊"类型的结果集上使用方法的一个子集，而 fetch_object() 不是其中之一(至少它是未明确列出).

assignes the resultset metadata, which is itself represented as a resultset, to the $result variable. According to the doc (http://www.php.net/manual/en/mysqli-stmt.result-metadata.php) you can only use a subset of the methods on these 'special' kinds of resultsets, and fetch_object() is not one of them (at least it is not explicitly listed).

也许是这些元数据结果集没有实现 fetch_object() 的错误，也许你应该在 bugs 提交错误.mysql.com 关于那个.

Perhaps it is a bug that fetch_object() is not implemented for these metadata resultsets, perhaps you should file a bug at bugs.mysql.com about that.

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