我对PHP完全陌生，需要检索所有值哪一个CONTAIN城市。但是，这会为每个城市返回多个文档。如何只显示一次而不显示多次城市？
所有项目都包含城市，包括几个项目都包含相同的城市，希望在我的下拉列表中只显示唯一的城市。正如现在的代码所示，上面显示的是所有城市。
<?php
$connection = new MongoClient( "" ); // connect to a remote host at a given port
$collection = $connection->value1->value2;
?>
<select name="City" class="form-control">
<option value="0">Please Select</option>
<?php $cursor = $collection->find()->sort( array( 'City' => 1 ) );
foreach ($cursor as $document) {
echo "<option value='" . $document["City"] . "'>" . $document["City"] . "</option>";
}
?>
</select>
这应该可以完成
//we will use several temporary values to remove the duplicate City's, values that will be of no use after we're done. thus i want to make a new scope for this.
//php scoping rules suck, and to create a new scope, we need to create a function, iirc.
call_user_func(function() use( &$cursor) { //declare and call a nameless function, and copy $cursor to this function's scope.
$a1 = array();
$unsetarr = array();
foreach($cursor as $key => $document) {//iterate $cursor
if (in_array($document["City"], $a1)) {
//if we have seen this city before, mark this $cursor entry for deletion.
//(we won't delete it right away because modifying the length of the array WHILE iterating it sounds like a bad idea. it certainly would be a bad idea in certain other languages. maybe PHP could handle it, but i don't know.)
$unsetarr[] = $key;
}
$a1[] = $document["City"];
}
foreach($unsetarr as $tounset) {
//delete all entries that was marked for deletion in the previous loop.
unset($cursor[$tounset]);
}
//maybe $cursor=array_values($cursor); to fix the keys
});