Hi,
I am trying to write a proper query_chooser method for our user based
sharding. To do so, I need to be able to query the value of the
query's criterions.
I have the following model:
class User(object):
id = Column(Integer, primary_key=True)
...
class Subscription(object):
id = Column(Integer, primary_key=True)
producerId = Column(Integer, ForeignKey('User.id'))
consumerId = Column(Integer) # No foreign key because sharded on
producerId
producer = relationship('User', backref='subscriptions')
In my query_chooser, I am using the code from the attribute_sharding
example and try to find out the value of producerId if there is such a
criterion.
Given an existing myUser instance and a session, I see two different
behaviors:
1. session.query(Subscription).filter(Subscription.producerId ==
myUser.id).all()
I will get a proper value for producerId in the dictionary of bound
parameters so I can find out the shard, no problem.
SELECT "InboundSubscription".s9id AS "InboundSubscription_s9id",
"InboundSubscription".active AS "InboundSubscription_active",
"InboundSubscription"."createdAt" AS "InboundSubscription_createdAt",
"InboundSubscription"."updatedAt" AS "InboundSubscription_updatedAt",
"InboundSubscription"."followerId" AS
"InboundSubscription_followerId", "InboundSubscription"."producerId"
AS "InboundSubscription_producerId", "InboundSubscription".status AS
"InboundSubscription_status", "InboundSubscription".suspended AS
"InboundSubscription_suspended"
FROM "InboundSubscription"
WHERE "InboundSubscription"."producerId" = :producerId_1
2. myUser.subscriptions
I get a None value for the anonymous parameter which prevents me from
picking a shard.
SELECT "InboundSubscription".s9id AS "InboundSubscription_s9id",
"InboundSubscription".active AS "InboundSubscription_active",
"InboundSubscription"."createdAt" AS "InboundSubscription_createdAt",
"InboundSubscription"."updatedAt" AS "InboundSubscription_updatedAt",
"InboundSubscription"."followerId" AS
"InboundSubscription_followerId", "InboundSubscription"."producerId"
AS "InboundSubscription_producerId", "InboundSubscription".status AS
"InboundSubscription_status", "InboundSubscription".suspended AS
"InboundSubscription_suspended"
FROM "InboundSubscription"
WHERE :param_1 = "InboundSubscription"."producerId"
When is this value populated? How can I access it in query_chooser?
Thanks in advance for you help. I am using sqlalchemy 0.7.1
Arthur
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