問題描述

我看到的所有使用 mysqli_fetch_object 的示例都使用 mysql_query()，我無法讓它與準備好的語句一起工作.有誰知道這段代碼有什么問題，因為 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();

輸出為:

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

推薦答案

我不相信界面是這樣工作的.

I don't believe the interface works like that.

通過文檔和示例(http://www.php.net/manual/en/mysqli.prepare.php) 似乎 $stmt->execute() 不返回結果集，而是一個指示成功/失敗的布爾值(http://www.php.net/manual/en/mysqli-stmt.execute.php).要實際獲得結果，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).

完成所有這些之后，您可以重復調用 $stmt->fetch() () 以使用當前行中的列值填充綁定變量.我沒有看到任何提及 $stmt->fetch_object() 的內容，也沒有看到該接口如何與描述的變量綁定方案一起工作.

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.

這就是從 mysqli 準備好的語句中獲取正常"結果的故事.

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

在您的代碼中，我懷疑存在錯誤，或者至少我不確定您是否打算這樣做.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();

將結果集元數據(本身表示為結果集)分配給 $result 變量.根據文檔 (http://www.php.net/manual/en/mysqli-stmt.result-metadata.php) 您只能在這些特殊"類型的結果集上使用方法的一個子集，而 fetch_object() 不是其中之一(至少它是未明確列出).

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).

也許是這些元數據結果集沒有實現 fetch_object() 的錯誤，也許你應該在 bugs 提交錯誤.mysql.com 關于那個.

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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