Rails中的多态关联(Polymorphic Associations in Rails)

 您需要使用声明Xpath表达式评估的名称空间前缀的名称空间上下文： 
 
receive(action -> action.endpoint(fooChannel)
        .namespace("ns", "http://domain/fault/2.0/")
        .validate("number:count(//ns:ValidationFault)", 1));
 
 默认情况下，Xpath表达式求值为节点值。 所以请确保使用count()函数来评估元素的数量。 
 
 作为替代方案，您可以评估节点集并使用Hamcrest匹配器hasSize() ： 
 
receive(action -> action.endpoint(fooChannel)
        .namespace("ns", "http://domain/fault/2.0/")
        .validate("node-set://ns:ValidationFault", Matchers.hasSize(1)));

You need to use a namespace context that declares the namespace prefixes for the Xpath expression evaluation:
 
receive(action -> action.endpoint(fooChannel)
        .namespace("ns", "http://domain/fault/2.0/")
        .validate("number:count(//ns:ValidationFault)", 1));
 
The Xpath expression evaluates to the node values by default. So please make sure to use count() function in order to evaluate the number of elements.
 
As an alternative to that you could evaluate to the node-set and use the Hamcrest matcher hasSize():
 
receive(action -> action.endpoint(fooChannel)
        .namespace("ns", "http://domain/fault/2.0/")
        .validate("node-set://ns:ValidationFault", Matchers.hasSize(1)));