mysql CRUD理解循环

Question

我正在关注有关mysql数据库中CRUD操作的教程，具体来说是与PDO一起使用的（尽管我认为这并不重要）。

它是一个时间跟踪器； 由项目表和任务表组成； 每个任务都属于一个项目。 一个项目可以有多个任务，但是一个任务只能属于一个项目。 我需要显示一个“报告”页面，其中将包括项目，然后是该项目的任务列表以及在每个任务上花费的时间，在每个项目结束时，将花费在该项目上的总时间。

这是显示报告的表； 最后一个项目没有总计，但这是在教程上进一步讨论的问题。

<?php 
$filter = 'all';
?>
<table>
  <?php 
  $total = $project_id = $project_total = 0;
  foreach (get_tasks_list($filter) as $item) {
      if ($project_id != $item['project_id']) {
          if ($project_id > 0) {
              echo '<tr>';
              echo '<th colspan="2">Project Total</th>';
              echo '<th>' . $project_total . '</th>';   
              echo '</tr>';
              $project_total = 0;
             }
             $project_id = $item['project_id'];
             echo '<thead>';
             echo '<tr>';
             echo '<td>' . $item['project'] . '</td>';
             echo '<td>  Date  </td>';
             echo '<td> Time </td>';
             echo '</tr></thead>';
         }    
         $project_total += $item['time'];
         $total += $item['time'];
         echo '<tr>';
         echo '<td>' . $item['title'] .  '</td>';
         echo '<td>' . $item['date'] .  '</td>';
         echo '<td>' . $item['time'] .  '</td>';
         echo '</tr>';
     }
  ?>
    <tr class="totalReportTime">
      <th colspan="2">Total</th>
      <th><?php echo $total; ?></th>
    </tr>
  </table>

get_tasks_list给出所有任务的列表。

这是报告表的外观：

我的疑问是.....我在做什么： $ project_id = $ item ['project_id']; ??

我的意思是.... foreach循环之后，foreach任务我检查我刚刚设置为0的$ project_id是否等于与该任务相关的project_id，但是，为什么我要说$ project_id是否更大大于0？ 为什么在它之后将$ project_id的值设置为与任务中的project_id相同的值？

基本上，我没有了解它如何“知道”它需要在最后添加每个项目的总数，或者为什么它要执行该分配$ project_id = $ item ['project_id'];

任何基本解释都会有所帮助。

谢谢！

Answer 1

我已经为每个代码部分添加了注释，以便您阅读它们并了解每个代码的重要性，还有任何问题请告诉我。

<?php 
$filter = 'all';
?>
<table>
    <?php 

  // variable declaration
    $total = $project_id = $project_total = 0;

  // fetaching all the tasks
    foreach (get_tasks_list($filter) as $item) {

        // $item['project_id'] --> it has the project_id shows this task belongs to this project
        // this condition checks that current project_id and task's  project id is matched or not
        // at first time $project_id will be zero so this will be true at first time
        // and next time when it will be set to another project id again this will be executed.
        // so in short this condition has 2 purpose
        // 1. show project total
        // 2. show project title
        // it will done once project is changed.                
        if ($project_id != $item['project_id']) {

            // at very first time we will not show total for first project
            // so we are comparing it will 0
            if ($project_id > 0) {

                // print total
                echo '<tr>';
                echo '<th colspan="2">Project Total</th>';
                echo '<th>' . $project_total . '</th>';   
                echo '</tr>';

                // once total is printed we need to reset it for another project
                $project_total = 0;
            }

            // this is needed for printing header only once for each tasks.
            // as if ($project_id != $item['project_id'])
            // this condition only pass when project is changed.
            // so it will print total and then header of project
            // then we will assign $project_id = $item['project_id'] as we need to tell loop
            // current project id is changed or not from previous iteration if its changed then 
            // again print total and header with this condition check if ($project_id != $item['project_id'])
            $project_id = $item['project_id'];
            echo '<thead>';
            echo '<tr>';
            echo '<td>' . $item['project'] . '</td>';
            echo '<td>  Date  </td>';
            echo '<td> Time </td>';
            echo '</tr></thead>';
        }    

        // this will be total for each task and you can see 
        // it is cleared in upper condition when project is changed
        $project_total += $item['time'];

        // this is grand total it will add all the time for all the task and not going to reset
        $total += $item['time'];

        // this will print each task
        echo '<tr>';
        echo '<td>' . $item['title'] .  '</td>';
        echo '<td>' . $item['date'] .  '</td>';
        echo '<td>' . $item['time'] .  '</td>';
        echo '</tr>';
    }
    ?>


    <tr class="totalReportTime">
        <th colspan="2">Total</th>
        <th><?php 
            // at last row we are printing main total
            echo $total; 
        ?></th>
    </tr>
</table>

最后一个项目没有总数

这是因为您可以看到它的最后一个任务，所以循环不会再次自我迭代，也不会比较project_id的变化，因此它不会达到这种状态，因此不会打印最后一个项目