How to know if query doesn't return documents

问题

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

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

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

Thank you!

回答1:

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

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")

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

来源：https://stackoverflow.com/questions/58838764/how-to-know-if-query-doesnt-return-documents