处理多个表到MySQL数据库的数据导出到XML

Question

我需要帮助与代码解释，所以我能理解如何处理多个表：

也有几个表名为

公寓，性质，类别，开发商

1. 公寓列（ID，CATEGORY_ID，developer_id，PROPERTY_ID， 标题，价格）
个
2. 类别列（ID，标题）
3. 开发商列（ID，标题）
4. 性质列（ID，标题，CATEGORY_ID）

如下两者之间的关系：

• category_id与id同步categories列表
• developer_id与同步列developers表
• property_id在properties表

同步与id列，我需要更新下面的PHP代码像

<?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> 

输出我使用此代码检索使来自一个表的数据

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

正如在comm ents，你想使用连接来获得你想要的值。左连接确保包含来自公寓表的所有记录，而来自其他表（如果有）的缺失值将作为NULL返回。

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); 

通知我的表设置别名（使SQL清洁剂），也为列，构建XML时使用。您可以循环播放结果，而不是分别为每列调用createElement。这是可能的，因为我已经将获取类型指定为关联数组，而不是默认的获取类型，该类型既是关联数字型的，也是数字型的。最后一个注意事项是，如果没有参数，则不需要prepare()和​​声明。只需运行query()就可以得到相同的结果。

<?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(); 

如果你是喂养这个数据到自己的服务，你可能要考虑JSON，而不是XML的。 JSON的简单的数据结构和PHP的非常简洁的内置功能将使这小得多的程序：

<?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);