Question

我需要通过解释代码来获得帮助，这样我才能理解如何处理多个表：

有几个名为

的表

公寓，物业，类别，开发商

公寓列（id，category_id，developer_id，property_id，标题，价格）
类别列（ID，标题）
开发人员专栏（id，title）
属性列（id，title，category_id）

他们之间的关系如下：

category_id与id表

categories

developer_id与id表

developers

property_id与id表

properties

我需要更新下面的PHP代码以使输出像那样

<?xml version="1.0" ?>
<list>  
    <property>
        <title>apartments_title</title >
        <price>apartments_price</price >
        <type>properties_title</type>
        <categoty>categories_title</categoty>
        <developer>developer_title</developer>
   </property>

</list>

我使用此代码从一个表中检索数据

header('Content-type: text/xml');

// INITIALIZE DOM OBJECT
$dom = new DOMDocument('1.0', 'UTF-8');
$dom->formatOutput = true;            
$dom->preserveWhiteSpace = false;

// CREATE ROOT AND APPEND TO DOCUMENT
$xmlRoot = $dom->createElement("list");
$xmlRoot = $dom->appendChild($xmlRoot);

// QUERY DATABASE
$db = new PDO('mysql:host=hostname;dbname=dbname','dbusername','password');
$stmt = $db->prepare("select * from apartments");
$stmt->execute();

// FETCH ROWS ITERATIVELY
while($row = $stmt->fetch()){
     // APPEND property AS CHILD OF ROOT
     $propertyNode = $xmlRoot->appendChild($dom->createElement('property'));

     // APPEND CHILDREN TO Property         
     $propertyNode->appendChild($dom->createElement('title', $row['title']));
     $propertyNode->appendChild($dom->createElement('price', $row['price']));
}
$stmt = null; 
$db = null;

// OUTPUT TO SCREEN
echo $dom->saveXML();

Answer 1

如评论中所述，您希望使用联接来获取所需的值。左连接确保包含来自apartments表的所有记录，而其他表（如果有）中的缺失值将返回为NULL。

SELECT a.title AS title, a.price AS price, p.title AS type,
    c.title AS category, d.title AS developer
FROM apartments a
LEFT JOIN properties p ON (a.property_id = p.id)
LEFT JOIN categories c ON (a.category_id = c.id)
LEFT JOIN developers d ON (a.developer_id = d.id);

注意我已经为表（为了使SQL更清晰）设置了别名，并且在构建XML时也使用了列。您可以循环显示结果，而不是分别为每列调用createElement。这是可能的，因为我已将fetch类型指定为关联数组，而不是默认的fetch类型，它既是关联的又是数字的。最后要注意的是，如果没有参数，则不需要prepare()和execute()语句。只需运行query()即可获得相同的结果。

<?php
header('Content-type: text/xml');

// INITIALIZE DOM OBJECT
$dom = new DOMDocument('1.0', 'UTF-8');
$dom->formatOutput = true;            
$dom->preserveWhiteSpace = false;

// CREATE ROOT AND APPEND TO DOCUMENT
$xmlRoot = $dom->createElement("list");
$xmlRoot = $dom->appendChild($xmlRoot);

// QUERY DATABASE
$db = new PDO('mysql:host=hostname;dbname=dbname','dbusername','password');
$stmt = $db->query("SELECT a.title AS title, a.price AS price, p.title AS type, c.title AS category, d.title AS developer FROM apartments a LEFT JOIN properties p ON (a.property_id = p.id) LEFT JOIN categories c ON (a.category_id = c.id) LEFT JOIN developers d ON (a.developer_id = d.id);");

// FETCH ROWS ITERATIVELY
while($row = $stmt->fetch(PDO::FETCH_ASSOC)){
    // APPEND property AS CHILD OF ROOT
    $propertyNode = $xmlRoot->appendChild($dom->createElement('property'));
    foreach ($row as $element=>$value) {
        // APPEND CHILDREN TO Property         
        $propertyNode->appendChild($dom->createElement($element, $value));
    }
}

// OUTPUT TO SCREEN
echo $dom->saveXML();

如果要将此数据提供给您自己的服务，您可能需要考虑使用JSON而不是XML。 JSON更简单的数据结构和PHP非常简洁的内置函数将使这个程序变得更小：

<?php
header('Content-type: application/json');    

// QUERY DATABASE
$db = new PDO('mysql:host=hostname;dbname=dbname','dbusername','password');
$stmt = $db->query("SELECT a.title AS title, a.price AS price, p.title AS type, c.title AS category, d.title AS developer FROM apartments a LEFT JOIN properties p ON (a.property_id = p.id) LEFT JOIN categories c ON (a.category_id = c.id) LEFT JOIN developers d ON (a.developer_id = d.id);");

// FETCH ROWS
$rows = $stmt->fetchAll(PDO::FETCH_ASSOC));

// OUTPUT TO SCREEN
echo json_encode($rows);

处理多个表以将mysql db数据导出到xml

1 个答案: