如何在MarkLogic中计算两个xs.date类型的天数差值？

Hey there! Let's work through this to get you the numeric day count you need. The issue you're hitting is that while your current approach uses a duration-related function, there's a more direct way to get a numeric result, plus we can fix up the existing method if needed.

First, let's restate your setup code for clarity:

var date1 = xs.date("2018-03-29"); 
var date2 = xs.date("2018-04-15");

Why Your Current Try Isn't Returning a Numeric Value #

When you subtract two xs.date values (date2 - date1), you end up with an xs:dayTimeDuration object. If fn.daysFromDuration is returning a duration instead of a number, it might be due to a syntax mismatch (like using camelCase instead of the standard kebab-case fn:days-from-duration) or environment-specific behavior. But even if that worked, there's a cleaner solution.

The Best Function: fn:days-between #

The fn:days-between function (available in XQuery 3.1+ and supported in tools like Saxon JS) is made exactly for this. It takes two xs.date parameters and returns an xs:integer—a pure numeric value—representing the days between the dates.

Here's how to use it:

var dayDifference = fn.daysBetween(date1, date2);

For your example dates (2018-03-29 to 2018-04-15), this will return 17 (since March has 31 days: 31-29 + 15 = 17)—exactly the numeric result you're after.

If fn:days-between Isn't Available #

If you're stuck in an environment that doesn't support fn:days-between, you can still use the duration approach correctly. Just ensure you're using the proper function syntax to extract the integer day count from the duration:

var durationDiff = date2 - date1;
var dayDifference = fn.daysFromDuration(durationDiff);
// Or use standard XQuery syntax: fn:days-from-duration($durationDiff)

This should pull the integer day count from the duration object. If it's still returning a duration, double-check your environment's docs to confirm the correct function name and return type.

内容的提问来源于stack exchange，提问作者Ryan