如何知道查询是否不返回文档 [英] How to know if query doesn't return documents

问题描述

我怎么知道文档是否为空?我不能做len(docs)

How can I know if docs is empty? I can't do len(docs)

docs = query.stream()
for doc in docs:
    // do something

我需要知道是否没有与查询匹配的文件

I need to know if there is no document that matches the query

谢谢！

推荐答案

由于stream()

Since stream() returns a generator, there won't be a trivial way to determine if it is empty without actually reading it.

到目前为止，最简单的解决方案将延迟知道，直到您经过循环为止.像这样:

By far the simplest solution would delay knowing until after you are past the loop. Something like this:

docs = query.stream()
stream_empty = True
for doc in docs:
  stream_empty = False
  # do something

if stream_empty:
  print("it was empty")
else:
  print("it wasn't empty")

否则，您将不得不围绕允许窥视的流的生成器构建自己的生成器.参见此问题.

Otherwise, you get into having to build your own generator around the stream's generator that allows peeking. See this question.

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