XPath: How to select elements based on their value?

 

I am new to using XPath and this may be a basic question. Kindly bear with me and help me in resolving the issue. I have an XML file like this: 

<RootNode>
  <FirstChild>
    <Element attribute1="abc" attribute2="xyz">Data</Element>
  <FirstChild>
</RootNode>

I can validate the presence of an <Element> tag with: 

//Element[@attribute1="abc" and @attribute2="xyz"]

Now I also want to check the value of the tag for string "Data" . For achieving this I was told to use: 

//Element[@attribute1="abc" and @attribute2="xyz" and Data]

When I use the later expression I get the following error:

Assertion failure message: No Nodes Matched //Element[@attribute1="abc" and @attribute2="xyz" and Data]

Kindly provide me with your advice whether the XPath expression I have used is valid. If not what will be the valid XPath expression?

The condition below: 

//Element[@attribute1="abc" and @attribute2="xyz" and Data]

checks for the existence of the element Data within Element and not for element value Data.

Instead you can use 

//Element[@attribute1="abc" and @attribute2="xyz" and text()="Data"]

//Element[@attribute1="abc" and @attribute2="xyz" and .="Data"]

The reason why I add this answer is that I want to explain the relationship of . and text() .

The first thing is when using [] , there are only two types of data:

  • *[number] to select a node from node-set
  • *[bool] to filter a node-set from node-set

    • In this case, the value is evaluated to boolean by function boolean() , and there is a rule:

    Filters are always evaluated with respect to a context.

    When you need to compare text() or . with a string "Data" , it first uses string() function to transform those to string type, than gets a boolean result.

    There are two important rule about string() :

  • The string() function converts a node-set to a string by returning the string value of the first node in the node-set, which in some instances may yield unexpected results.

    text() is relative path that return a node-set contains all the text node of current node(context node), like ［"Data"］ . When it is evaluated by string(["Data"]) , it will return the first node of node-set, so you get "Data" only when there is only one text node in the node-set.

  • If you want the string() function to concatenate all child text, you must then pass a single node instead of a node-set.

    For example, we get a node-set ['a', 'b'] , you can pass there parent node to string(parent) , this will return 'ab' , and of cause string(.) in you case will return an concatenated string "Data" .

    • Both way will get same result only when there is a text node.

    链接地址: http://www.djcxy.com/p/78162.html

    上一篇: 通过XPath提取属性节点的值

    下一篇: XPath：如何根据它们的值选择元素？