XPath 1.0中PaymentDate为nil时替换为AccountingDate的实现方案

I’ve run into similar XPath 1.0 limitations before, so I know how annoying it is when the fancier 2.0+ functions aren’t on the table. Let’s work through this problem step by step:

The Core Approach #

Since we can’t use nilled() and boolean(PaymentDate) still returns true for nil-marked nodes, we’ll directly check for the xsi:nil="true" attribute to decide which value to pull.

Working XPath Expressions #

Option 1 (Prefix-Assumed)

If your XML parser already maps the xsi prefix to the http://www.w3.org/2001/XMLSchema-instance namespace (which most do for valid XML), use this clean version:

(PaymentDate[not(@xsi:nil='true')] | AccountingDate[PaymentDate/@xsi:nil='true'])/text()

Option 2 (Namespace-Agnostic)

If you can’t rely on the xsi prefix being configured, target the nil attribute directly using its namespace URI and local name:

(
  PaymentDate[not(@*[local-name()='nil' and namespace-uri()='http://www.w3.org/2001/XMLSchema-instance']='true')] 
  | 
  AccountingDate[PaymentDate/@*[local-name()='nil' and namespace-uri()='http://www.w3.org/2001/XMLSchema-instance']='true']
)/text()

How It Works #

For each EventDetails node:

• The first segment selects the PaymentDate node only if it doesn’t have the xsi:nil="true" attribute, then extracts its text value.
• The second segment selects the AccountingDate node only if the corresponding PaymentDate is marked nil, then extracts its text value.
• The | operator combines these node sets, and since each EventDetails will match exactly one condition, you’ll get the correct value per event.

Testing with Your XML #

• For the first EventDetails: PaymentDate has no nil attribute, so you’ll get 2017-01-31.
• For the second EventDetails: PaymentDate is marked nil, so you’ll fall back to AccountingDate’s value 2017-01-01.

内容的提问来源于stack exchange，提问作者user9267428