以下代码：
<？php try { $ dbh = new PDO （mysql：host = $ hostname; dbname = $ dbname，$ username，$ password）; echo连接成功！< br />; $ sql =SELECT * FROM users; $ users = $ dbh-> query（$ sql）; foreach（$ users为$ row）{ print $ row [name]。 - 。 $ row [sex]。< br />; } foreach（$ users as $ row）{ print $ row [name]。 - 。 $ row [sex]。< br />; } $ dbh = null; } catch（PDOexception $ e）{ echo错误是：。 $ E-> etmessage（）; $ / code $ / pre $ b $输出： 连接成功！ 个人A-male 人B-female跑步foreach两次不是我的目的，我只是好奇为什么两个foreach语句只输出一次结果？
以下是类似的情况：
<？php try { $ dbh = new PDO（mysql：host = $ hostname; dbname = $ dbname，$ username，$ password）; echo连接成功！< br />; $ sql =SELECT * FROM users; $ users = $ dbh-> query（$ sql）; foreach（$ users为$ row）{ print $ row [name]。 - 。 $ row [sex]。< br />; } echo< br />; $ result = $ users-> fetch（PDO :: FETCH_ASSOC）; foreach（$ result为$ key => $ value）{ echo $ key。 - 。 $值。 <峰; br /> 中; } $ dbh = null; } catch（PDOexception $ e）{ echo错误是：。 $ E-> etmessage（）; $ / code $ / pre $ b $输出： 连接成功！ 个人A-male 个人B-female SCREAM：忽略的错误抑制警告：为foreach（）提供的无效参数但是当我从上面的代码中删除第一个foreach时，输出就会正常：
$ $ dbname，$ username，$ password）; echo连接成功！< br />; $ sql =SELECT * FROM users; $ users = $ dbh-> query（$ sql）; echo< br />; $ result = $ users-> fetch（PDO :: FETCH_ASSOC）; foreach（$ result为$ key => $ value）{ echo $ key。 - 。 $值。 <峰; br /> 中; } $ dbh = null; } catch（PDOexception $ e）{ echo错误是：。 $ E-> etmessage（）; $ / code $ / pre $ b $输出： 连接成功！ user_id-0000000001 name-person A sex-male有人知道为什么会发生这种情况？我只是一个PHP初学者，感谢您的帮助！
解决方案A PDOStatement （你有 $ users ）是一个前向游标。这意味着，一旦消费（第一个 foreach 迭代），它不会倒回到结果集的开始处。
<您可以在 foreach 之后关闭游标并再次执行语句： $ users = $ dbh-> query（$ sql）; foreach（$ users为$ row）{ print $ row [name]。 - 。 $ row [sex]。< br />; } $ users-> execute（）; foreach（$ users为$ row）{ print $ row [name]。 - 。 $ row [sex]。< br />; $ / code>或者您可以使用定制的 CachingIterator with a fullcache：
$ users = $ dbh-> query（$ sql）; $ usersCached =新的CachedPDOStatement（$ users）; foreach（$ usersCached as $ row）{ print $ row [name]。 - 。 $ row [sex]。< br />; } foreach（$ usersCached as $ row）{ print $ row [name]。 - 。 $ row [sex]。< br />;您找到 CachedPDOStatement 类作为要点。缓存itertor可能比将结果集存储到数组中更为理智，因为它仍然提供了它所包装的 PDOStatement 对象的所有属性和方法。 b
The following codes:
<?php try { $dbh = new PDO("mysql:host=$hostname;dbname=$dbname", $username, $password); echo "Connection is successful!<br/>"; $sql = "SELECT * FROM users"; $users = $dbh->query($sql); foreach ($users as $row) { print $row["name"] . "-" . $row["sex"] ."<br/>"; } foreach ($users as $row) { print $row["name"] . "-" . $row["sex"] ."<br/>"; } $dbh = null; } catch (PDOexception $e) { echo "Error is: " . $e-> etmessage(); }OUTPUT:
Connection is successful! person A-male person B-femaleRunning "foreach" twice is not my purpose, I'm just curious why TWO "foreach" statements only output the result once?
Following is the similar case:
<?php try { $dbh = new PDO("mysql:host=$hostname;dbname=$dbname", $username, $password); echo "Connection is successful!<br/>"; $sql = "SELECT * FROM users"; $users = $dbh->query($sql); foreach ($users as $row) { print $row["name"] . "-" . $row["sex"] ."<br/>"; } echo "<br/>"; $result = $users->fetch(PDO::FETCH_ASSOC); foreach($result as $key => $value) { echo $key . "-" . $value . "<br/>"; } $dbh = null; } catch (PDOexception $e) { echo "Error is: " . $e-> etmessage(); }OUTPUT:
Connection is successful! person A-male person B-female SCREAM: Error suppression ignored for Warning: Invalid argument supplied for foreach()But when I delete the first "foreach" from the above codes, the output will become normal:
<?php try { $dbh = new PDO("mysql:host=$hostname;dbname=$dbname", $username, $password); echo "Connection is successful!<br/>"; $sql = "SELECT * FROM users"; $users = $dbh->query($sql); echo "<br/>"; $result = $users->fetch(PDO::FETCH_ASSOC); foreach($result as $key => $value) { echo $key . "-" . $value . "<br/>"; } $dbh = null; } catch (PDOexception $e) { echo "Error is: " . $e-> etmessage(); }OUTPUT:
Connection is successful! user_id-0000000001 name-person A sex-maleAnyone know why does this happen? I'm just a PHP beginner, thanks for your help!
解决方案A PDOStatement (which you have in $users) is a forward-cursor. That means, once consumed (the first foreach iteration), it won't rewind to the beginning of the resultset.
You can close the cursor after the foreach and execute the statement again:
$users = $dbh->query($sql); foreach ($users as $row) { print $row["name"] . "-" . $row["sex"] ."<br/>"; } $users->execute(); foreach ($users as $row) { print $row["name"] . "-" . $row["sex"] ."<br/>"; }Or you could cache using tailored CachingIterator with a fullcache:
$users = $dbh->query($sql); $usersCached = new CachedPDOStatement($users); foreach ($usersCached as $row) { print $row["name"] . "-" . $row["sex"] ."<br/>"; } foreach ($usersCached as $row) { print $row["name"] . "-" . $row["sex"] ."<br/>"; }You find the CachedPDOStatement class as a gist. The caching itertor is probably more sane than storing the resultset into an array because it still offers all properties and methods of the PDOStatement object it has wrapped.
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