派生函数中的 last()

Question

为什么 fn:last() 功能在生成时不起作用？

这失败了：

xquery version "1.0-ml";
let $items := (1, 2, 3)
return xdmp:spawn-function(function () {
   $items[3 to fn:last()] 
})

一段时间后我取消了作业，因为它什么都不做。

Output: Cancelling fails with message indication function must be stopped manually.

这很好用：

xquery version "1.0-ml";
let $items := (1, 2, 3)[3 to fn:last()] 
return xdmp:spawn-function(function () {
   $items
})

Output: Query completed successfully

Answer 1

fn:last() is showing a very similar usage of this function. The downside for using functions in predicates is though that they are evaluated for each item in the sequence. Using fn:subsequence and optionally fn:count 文档的示例应该更有效，并且绕过您的问题：

let $items := (1, 2, 3)
return xdmp:spawn-function(function () {
   xdmp:log(subsequence($items, 3, count($items))) (: you can omit 3rd param with same effect :)
})

HTH！

派生函数中的 last()

last() in spawned functions

xquery

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