为分页 API 制作 Scala 迭代器

问题描述

我正在编写一个 Scala 库，以便更轻松地查询分页的 JSON API.每个 API 调用都会返回一个如下所示的对象:

I'm writing a Scala library to make querying an paginated JSON API easier. Each API call returns an object that looks something like this:

{
  "count": 100,
  "current_page": 1,
  "total_pages": 2,
  "records": [
    ...
  ]
}

我想要一个返回某种迭代器的函数，比如 MyIterator[Record].在 Scala 世界中是否有任何标准方法可以做到这一点，甚至标准库中的构造可以帮助我?

I'd like to have a function that returned some sort of iterator like MyIterator[Record]. Are there any standard ways to do this in the Scala world, perhaps even constructs in the standard library that could help me?

如果有帮助的话，我通常使用 lift-json 来解析 JSON.

I'm using lift-json generally for my JSON parsing, if that's helpful.

谢谢.

推荐答案

如果你有一个 Iterator[Iterator[A]] 你可以使用 flatten 来产生一个 Iterator[Iterator[A]]code>Iterator[A] 将所有嵌套的迭代器链接在一起:

If you have an Iterator[Iterator[A]] you can use flatten to produce an Iterator[A] which chains all the nested Iterators together:

scala> Iterator(Iterator(1, 2), Iterator(3, 4)).flatten.toList
res0: List[Int] = List(1, 2, 3, 4)

结合 Iterator 上的一种工厂方法 companion对象，你可以把它变成一个单行:

Combined with one of the factory methods on the Iterator companion object, you could probably turn this into a one-liner:

Iterator.range(1, pageCount).map(i: Int => fetchPage(i)).flatten

如果您只能通过检索页面来获取页面计数，则可能需要更复杂一些……例如:

It might need to be a bit more complex if you can only get the page count by retrieving a page... something like:

val (firstPage, pageCount) = getFirstPageWithCount()
firstPage ++ (Iterator.range(2, pageCount).map(fetchPage).flatten)

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