NDB查询构建器无法按预期工作

Question

I have the following query in my application

query = cls.query().filter(cls.taskgroup_id == taskgroup_id, cls.availability == True, cls.task_id > min_task_id).order(cls.task_id) query.fetch(1)

Above works fine as expected. (Fetches only those entities, which match taskgroup_id, and is available, and task_id > min_task_id)

However, when I break query into multiple statements.

query = cls.query()
query.filter(cls.taskgroup_id == taskgroup_id)
query.filter(cls.availability == True)
query.filter(cls.task_id > min_task_id)

It doesn't work as expected.

When I run [2], query formation broken down into multiple statements, it returns me a entity whose availability is False, and task_id is equal to min_task_id.

[2] doesn't work as expected (or as I expect). I think there is a user error here. Wondering what it is.

Answer 1

From Filtering by Property Values (emphasis mine):

 query = Account.query(Account.userid >= 40, Account.userid < 50) 

[...]

Instead of specifying an entire query filter in a single expression, you may find it more convenient to build it up in steps: for example:

appengine/standard/ndb/queries/snippets.py

 query1 = Account.query() # Retrieve all Account entitites query2 = query1.filter(Account.userid >= 40) # Filter on userid >= 40 query3 = query2.filter(Account.userid < 50) # Filter on userid < 50 too 

query3 is equivalent to the query variable from the previous example. Note that query objects are immutable , so the construction of query2 does not affect query1 and the construction of query3 does not affect query1 or query2 .

In other words for your example none of the query.filter() statements actually modifies query .

Just assign the results of the statements to local variables and use those instead, just as in the quoted example.