问题
What is a good way to get the number of query result when using NDB on google app engine?
Attempted this:
query = NDB_Model.query(NDB_Model.some_property == some_value)
if len(query) > 0: # <-- this throws and exception
entity = query[0]
I apologize that this is probably a very simple question, but it was not clear to me from the docs.
回答1:
It seems like you just want to get the first entity from your query. That's what query.get() is for.
query = NDB_Model.query(NDB_Model.some_property == some_value)
entity = query.get()
if entity is not None:
# Do stuff
From the docs:
Returns the first query result, if any (otherwise None). This is similar to calling q.fetch(1) and returning the first item of the list of results.
In a more general form, there's query.fetch(n) where n is the maximum number of entities to fetch. It returns a list, so you could easily check len() on that.
回答2:
To get the result count of a ndb query you can simply use count():
query = NDB_Model.query(NDB_Model.some_property == some_value)
if query.count() > 0:
entity = query[0]
来源：https://stackoverflow.com/questions/12220653/get-ndb-query-length-using-python-on-google-app-engine