xml XPath查询如何根据两个属性获取一个属性的值
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XPath query how to get value of one attribute based on two attribute
提问by Umesh K
I want to extract name attribute value from the following tag
我想从以下标签中提取名称属性值
<application
comments="Do not erase this one"
executable="run_CIET"
icon="default"
instances="1"
mode="1"
name="CIET"
order="10"
selection="1"
tool="y"
/>
I can easily get value of name attribute value based on mode value as shown below
我可以根据模式值轻松获取名称属性值的值，如下所示
xpath Applications.xml '//applications/application[@mode='3']'/@name
But if I want to add more condtion which is "get name attribute value when mode=X and tool attribute is not there in application tag"
但是，如果我想添加更多条件，即“在应用程序标记中不存在模式 = X 且工具属性时获取名称属性值”
How do we do this? I tried something like
我们如何做到这一点？我试过类似的东西
xpath Applications.xml '//applications/application[@mode='3' and !@tool]'/@name
but its not working.
但它不工作。
I have not used XPath before and I am finding it tricky I search W3C help on XPath but did not find what I wanted. Please help.
我以前没有使用过 XPath，我发现它很棘手 我在 XPath 上搜索 W3C 帮助但没有找到我想要的。请帮忙。
回答by Dimitre Novatchev
How do we do this? I tried something like
xpath Applications.xml '//applications/application[@mode='3' and !@tool]'/@name
but its not working.
!@tool
is invalid syntax in XPath. There is an !=operator, but no !operator.
是 XPath 中的无效语法。有!=操作员，但没有!操作员。
Use:
使用：
//applications/application[@mode='3' and not(@tool)]/@name
There are two things you should always try to avoid:
您应该始终尽量避免两件事：
using the
!=operator -- it has weird definition and doesn't behave like thenot()function --never use it if one of the operands is a node-set.Try to avoid as much as possible using the
//abbreviation -- this may cause signifficant inefficiency and also has anomalous behavior that isn't apperent to most people.
使用
!=运算符——它有奇怪的定义，并且不像not()函数——如果其中一个操作数是节点集，就不要使用它。尽量避免使用
//缩写——这可能会导致显着的低效率，并且还会有大多数人不知道的异常行为。
回答by Flynn1179
Using not(@tool)instead of !@toolshould do the job. If your XPath engine's not behaving you could conceivably do count(@tool)=0, but that shouldn't be necessary.
使用not(@tool)而不是!@tool应该可以完成这项工作。如果您的 XPath 引擎不工作，您可以想象这样做count(@tool)=0，但这不是必需的。
