无法执行不同的投影查询

Question

我有一个简单的小"Observation"class:

from google.appengine.ext import ndb

class Observation(ndb.Model):
    remote_id = ndb.StringProperty()
    dimension_id = ndb.IntegerProperty()
    metric = ndb.StringProperty()
    timestamp_observed = ndb.StringProperty()
    timestamp_received = ndb.DateTimeProperty(auto_now_add=True)

    @classmethod
    def query_book(cls):
        return cls.query()

我可以 运行 将针对数据存储的查询投影到 return 仅某些列。例如：

observations = Observation.query().fetch(projection=[Observation.dimension_id])

效果很好，但我只想要独特的结果。 documentation 让这听起来很简单：

# Functionally equivalent
Article.query(projection=[Article.author], group_by=[Article.author])
Article.query(projection=[Article.author], distinct=True)

但是当我这样做时：

observations = Observation.query().fetch(projection=[Observation.dimension_id], group_by=[Observation.dimension_id])
observations = Observation.query().fetch(projection=[Observation.dimension_id], distinct=True)

两种变体都出现错误。

TypeError: Unknown configuration option ('group_by')
TypeError: Unknown configuration option ('distinct')

这发生在 localhost 和 prod 环境中。我错过了什么？

Answer 1

愚蠢的我 - 所有这些参数都需要位于 query() 函数中，而不是 fetch() 中。投影元素实际上在 fetch() 中起作用，但您需要将投影和不同的参数都移到 query() 中才能使其起作用。

来自Grouping：

Projection queries can use the distinct keyword to ensure that only completely unique results will be returned in a result set. This will only return the first result for entities which have the same values for the properties that are being projected.

Article.query(projection=[Article.author], group_by=[Article.author])
Article.query(projection=[Article.author], distinct=True)

Both queries are equivalent and will produce each author's name only once.

希望这对遇到类似问题的其他人有所帮助:)