php - 如何只为 php foreach 循环结果回显一条消息并在没有结果时隐藏该消息？

Question

您好，我正在尝试为 php foreach 循环的结果显示一条通用消息。该消息必须在结果之前显示，如果没有结果则不应显示。

<!-- An array coming from the previous page -->
$string = explode(PHP_EOL, trim($_SESSION['grid']));

<!-- HIDE THIS MESSAGE IF THERE ARE NO RESULTS --> 
<label>These barcodes don't exist:</label>   

foreach ($string as $value) {
    <!-- SQL QUERY -->
    $query1 = "select addl_item_code_barcode from items where 
    addl_item_code_barcode = '$value';";
    $result = pg_query($db, $query1);

    <!-- IF THE VALUES IN THE ARRAY DON'T EXIST IN THE DATABASE THEN IT IS TO 
    BE DISPLAYED -->
    if (pg_num_rows($result) == 0) {
        echo $value; echo' ';
    } 
}

问题是循环外不会显示多个值，循环前不会显示结果。我该如何解决这个问题？

Answer 1

不要立即回显你的输出，而是将它存储在一个字符串变量中，然后在你的标签之后输出

<?php
// An array coming from the previous page
$string = explode(PHP_EOL, trim($_SESSION['grid']));
$values = "";

foreach ($string as $value) {
    <!-- SQL QUERY -->
    $query1 = "
        SELECT addl_item_code_barcode 
          FROM items 
         WHERE addl_item_code_barcode = '$value'
             ;
    ";
    $result = pg_query($db, $query1);

    // IF THE VALUES IN THE ARRAY DON'T EXIST IN THE DATABASE THEN IT IS TO BE DISPLAYED
    if (pg_num_rows($result) == 0) {
        $values .= "{$value} ";
    } 
}

if (strlen($values) === 0) {
    // HIDE THIS MESSAGE IF THERE ARE NO RESULTS
    ?><label>These barcodes don't exist:</label><?php
}