概念 XML XLST 前兄弟和祖先

Concept XML XLST preceding-sibling and ancestor

提问by olo

I am very new to xslt, and found it can be easy or complex. I want to make clear some concepts. What is preceding-sibling and what is ancestor, after searching from google, I found ancestor explanation. and the chart from their website makes easier to understand.

我对 xslt 很陌生，发现它可以很简单也可以很复杂。我想澄清一些概念。什么是前兄弟，什么是祖先，在google上搜了一下，找到了祖先的解释。他们网站上的图表更容易理解。

But I still don't understand preceding-sibling

但我还是不明白前辈

<product>
    <inventory>
        <drink>
            <lemonade>
                <price>.50</price>
                <amount>20</amount>
            </lemonade>
            <pop>
                <price>.50</price>
                <amount>10</amount>
            </pop>
        </drink>
          <service>
           <address />
            <phone />
            <delivery> City </delivery>
          </service>      
        <snack>
            <chips>
                <price>.50</price>
                <amount>60</amount>
            </chips>
        </snack>
        <hotfood></hotfood>
         <totalprice> </totleprice>

    </inventory>
</product>

so how do I read this preceding-sibling::pop/ancestor::inventory/totalprice

那么我如何阅读这个previous-sibling::pop/ancestor::inventory/totalprice

ancestor::inventory/totalprice = product\inventory\totalprice preceding-sibling::pop - I dont understand this one then how to read all together?

祖先::库存/总价 = 产品\库存\总价previous-sibling::pop - 我不明白这个，那么如何一起阅读？

Many thanks

非常感谢

回答by Sean B. Durkin

The preceding-sibling:: axis

前兄弟::轴

The preceding-sibling::axis is an axis of navigation that includes all the preceding sibling elements to the focus element. By "sibling" we mean a different element which has the same parent to the reference item. By "preceding" we mean a node that occurs before the reference one. The order of the preceding-siblingaxis is the reverse document order. Take a look at this document:

该preceding-sibling::轴是导航的轴线，包括所有前述同级元素的聚焦元件。“兄弟”是指与参考项具有相同父项的不同元素。“在前”是指在参考节点之前出现的节点。preceding-sibling轴的顺序与文档顺序相反。看看这个文件：

<fruit>
  <banana>
   <lady-finger-banana/>
  </banana> 
  <apple/>
  <pear/>
  <kiwi/>
</fruit>

If the focus node is pear, then the sequence preceding-sibling::*is ...

如果焦点节点是梨形，那么序列preceding-sibling::*是...

1. apple
2. banana

1. 苹果
2. 香蕉

Note: fruit, pear, lady-finger-banana and kiwi are not in the sequence.

注：水果、梨、手指香蕉和猕猴桃不在序列中。

So the following is true:

所以以下是正确的：

• preceding-sibling::*[ 1]is the apple
• preceding-sibling::*[ 2]is the banana
• count( preceding-sibling::*)is 2
• preceding-sibling::apple[ 1]is also the apple
• preceding-sibling::banana[ 1]is the banana
• preceding-sibling::*[ 3]is absent or the empty sequence

• preceding-sibling::*[ 1]是苹果
• preceding-sibling::*[ 2]是香蕉吗
• count( preceding-sibling::*)是 2
• preceding-sibling::apple[ 1]也是苹果
• preceding-sibling::banana[ 1]是香蕉吗
• preceding-sibling::*[ 3]不存在或空序列

preceding-sibling::pop/ancestor::inventory/totalprice Example

前兄弟::流行/祖先::库存/总价格示例

We have to alter your sample document a little bit to usefully study this example

我们必须稍微修改您的示例文档以有效地研究此示例

<product>
    <inventory>
        <drink>
            <lemonade>
                <price>.50</price>
                <amount>20</amount>
            </lemonade>
            <pop>
                <price>.50</price>
                <amount>10</amount>
            </pop>
            <focus-item />
         </drink>
        <totalprice></totalprice>  
    </inventory>
</product>

Let us say the focus is on the element focus-item. To evaluate the expression preceding-sibling::pop/ancestor::inventory/totalpricefollow these steps:

假设焦点在元素 focus-item 上。要评估表达式，请执行preceding-sibling::pop/ancestor::inventory/totalprice以下步骤：

1. preceding-sibling::popselects all the preceding popelements to focus-item. This evaluates to a sequence of one node.

2. For each item in the left hand sequence (just one popelement it so happens), set this item as a temporary focus item, and evaluate the expression of the right of the / operator which is ...

   ancestor::inventory
   

   There is only one such node, which is the ancestral inventory node. Thus the first / operator evaluates to a sequence of one inventory node.

3. Now we evaluate the effect of the second / and its right-hand operand expression total price. For each item in the left hand sequence (just one inventory node so it happens), set this as a temporary focus item and evaluate totalprice.

4. totalpriceis short for child::totalprice. There is only one total price element on the child axis of the temporary focus node, so the final result is a sequence of one node, which is the total price node.

1. preceding-sibling::pop选择所有前面的pop元素来关注项目。这评估为一个节点的序列。

2. 对于左侧序列中的每个项目（pop它只是一个元素），将此项目设置为临时焦点项目，并评估 / 运算符右侧的表达式，即...

   ancestor::inventory
   

   只有一个这样的节点，即祖先库存节点。因此，第一个 / 运算符评估为一个库存节点的序列。

3. 现在我们评估第二个 / 及其右侧操作数表达式总价的影响。对于左侧序列中的每个项目（只有一个库存节点，所以它发生了），将其设置为临时焦点项目并评估totalprice。

4. totalprice是 的缩写child::totalprice。临时焦点节点的子轴上只有一个总价元素，所以最终结果是一个节点的序列，即总价节点。

Understanding by Diagrams

通过图表理解

Here is a diagram for preceding-sibling::. In it the reference node is Charlie and the node on the preceding-sibling::axis is in green. It is the only such node.

这是一个图表preceding-sibling::。其中，参考节点为 Charlie，preceding-sibling::轴上的节点为绿色。它是唯一的这样的节点。

回答by OkieOth

Axes useful for navigation through the node tree. So it depends from your problem what kind of axis is useful.

轴可用于在节点树中导航。所以这取决于你的问题什么样的轴是有用的。

The following stylesheet illustrates the difference.

以下样式表说明了差异。

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"  version="1.0">
   <xsl:output method="xml" indent="yes"/>

   <xsl:template match="snack">
        <xsl:variable name="siblings" select="ancestor::node()"/>
        <debug>
        <xsl:for-each select="preceding-sibling::node()">
                <sibling>
                        <xsl:value-of select="local-name()"/>
                </sibling>
        </xsl:for-each>
        <xsl:for-each select="ancestor::node()">
                <ancestor>
                        <xsl:value-of select="local-name()"/>
                </ancestor>
        </xsl:for-each>

        </debug>
   </xsl:template>

   <xsl:template match="*">
         <xsl:apply-templates select="*"/>
   </xsl:template>
</xsl:stylesheet>

回答by RetroCoder

Preceding-sibling gets all element siblings that preceded it in the current node level. Unless you specify one or more of those preceding siblings with an xpath expression. If you specify a specific preceding-sibling with xpath it always starts with 1 in square brackets.

Preceding-sibling 获取当前节点级别中位于它之前的所有元素同级。除非您使用 xpath 表达式指定一个或多个前面的同级。如果您使用 xpath 指定特定的前同级，则它始终以方括号中的 1 开头。

Ancestor is the first matching ancestor that matches the expression. So it goes back up the node tree to look at a matching expression based on where you currently are pointing. So if you were at product/inventory/drink/pop or just /pop then ancestor inventory/totalprice just looks for the frist occurence and it should only return back a pointer to point to that matching case else it will be pointing to nothing and you'll still be pointing at pop.

祖先是与表达式匹配的第一个匹配祖先。因此，它返回节点树以查看基于您当前指向的位置的匹配表达式。因此，如果您在 product/inventory/drink/pop 或只是 /pop 然后祖先库存/totalprice 只查找第一次出现，它应该只返回一个指向该匹配案例的指针，否则它将指向任何内容，而您'仍将指向流行音乐。