要求：处理有序的学生记录流。该流由学生记录组组成。每个组由 at 'sid' 列标识。
- 每个 StudentGroup 都包含在一个 HTML 表格中
- 每个 StudentRecord 都是表格的一行
我喜欢做的是根据数据构造代码。数据结构如下：
StudentRecordGroup 的迭代
每个 StudentRecordGroup 由以下序列组成：
请注意，此过程中没有条件语句！
现在，我们如何构建代码来做到这一点。您不能使用foreach 循环！这只在循环结束时进行读取。
我们有两个循环：
- 处理所有记录组的外部循环。
- 处理一个完整组的内循环。
执行此操作的技术称为“预读”。这就是它所说的。您在开始外循环之前读取了第一条记录。
来源：
Working Code at Pastebin.com
输出：
SID Date FName LName activity time score
2 John Ppap 12 56 56
2 John Ppap 23 23 23
SID Date FName LName activity time score
3 Mito Mmito 34 12 12
3 Mito Mmito 45 45 45
SID Date FName LName activity time score
4 Uba Uuba 56 78 100
代码：
<?php // 53020396/how-to-display-grouped-data-in-separate-tables-with-a-php-loop
/* ---------------------------------------------------------------------------
* The input stream consists of an Ordered Iteration of:
* A collection of Individual Records for each Student (StudentRecordGoup)
*
* Each StudentRecordGoup consists of a Sequence of:
* Start of Group
* Iteration of Student records belonging to the group
* End of Group
*
* Notice: There is no 'IF' statement anywhere in the control logic for a group!
*
* Please note: There is exactly one place in the code to assign any appropriate action!
* i.e. The structure of the code exactly matched the structure of the data. :)
*
* This makes it easier to debug, maintain and amend?
*
* To do this we need 'state' information. Specifically that a record is part
* of the current 'student record group' group or not. How do we do this?
*
* We always need a record to test! Including at the start! We never read a record
* and then decide what to do with it. We always know where we are in the data
* structure and either the current record belongs to the group or not.
*
* We need to use a technique called 'Read Ahead'. Literally, There is always
* a record to process. You don't have to test it to know where you are.
* Once you process it then you immediately read the next record from the input.
* i.e. You end up reading a new record NOT JUST AT THE WND OF THE LOOP!
* You cannot use 'foreach' loops.
*
* We have to include Initialisation to setup code and any termination code.
*
* I will put all the 'action place holders' in functions. That way it avoids
* obscuring the high-level logic.
*/
// Get the ordered student detail records
$pdo = getPdoConnection();
$pdoResultSet = prepareAndExecuteQuery($pdo);
// Process all the students Record Groups - 'read ahead' of the row
$curStudentRecord = $pdoResultSet->fetch(); // is assoc array
while ($curStudentRecord !== false) { // process the student record groups
// process one complete student group...
$curStudentRecordGroupId = $curStudentRecord['sid'];
startStudendRecordGroup($curStudentRecordGroupId);
while ( $curStudentRecord !== false // check record belongs to the current group
&& $curStudentRecord['sid'] === $curStudentRecordGroupId) {
processStudentRecord($curStudentRecord);
$curStudentRecord = $pdoResultSet->fetch(); // read the next record
}
endStudendRecordGroup($curStudentRecordGroupId); // ignore the current record
// that is the next group!
}
// all groups have been processed
exit;
/* --------------------------------------------------------------------------
* Student record group processing
*/
function startStudendRecordGroup($curStudentRecordGroupId)
{
echo "<!-- new group: sid = $curStudentRecordGroupId -->";
echo "<table><tr><th>SID</th><th>Date</th><th>FName</th><th>LName</th>
<th>activity</th><th>time</th><th>score</th></tr>";
}
function processStudentRecord($curStudentRecord)
{
echo "<!-- group record: sid = {$curStudentRecord['sid']} -->";
echo "<tr>
<td>" . $curStudentRecord['sid'] . "</td>
<td>" . $curStudentRecord['fname'] . "</td>
<td>" . $curStudentRecord['lname'] . "</td>
<td>" . $curStudentRecord['col3'] . "</td>
<td>" . $curStudentRecord['col4'] . "</td>
<td>" . $curStudentRecord['col5'] . "</td>
</tr>";
}
function endStudendRecordGroup($curStudentRecordGroupId)
{
echo "<!-- end group: sid = $curStudentRecordGroupId -->";
echo "</table>";
}
/* --------------------------------------------------------------------------
* Database access
*/
// Execute query and return 'resultset'
function prepareAndExecuteQuery(\PDO $pdo)
{
$sql = 'SELECT id, sid, fname, lname, col3, col4, col5
FROM activity
ORDER BY sid, id';
$stmt = $pdo->prepare($sql);
$allOk = $stmt->execute();
return $stmt;
}
// DB Connection
function getPdoConnection()
{
$opt = array(
\PDO::ATTR_ERRMODE => \PDO::ERRMODE_EXCEPTION,
\PDO::ATTR_DEFAULT_FETCH_MODE => \PDO::FETCH_ASSOC,
\PDO::ATTR_EMULATE_PREPARES => false,
);
$pdo = new \PDO('mysql:host=localhost;dbname=notmydb;', 'notme', 'notme', $opt);
return $pdo;
}