On Aug 1, 2011, at 5:08 PM, Ross Vandegrift wrote:
> Hello everyone,
>
> Trying to use hybrid_attribute to provide friendly names for integers
> representing object states. Storage and retrieval works fine, but I
> can't get filtering working. I want the translation to happen on the
> Python side prior to filling in the query parameters, but
> hybrid_attribute is thinking the DB should do it. Example at the
> bottom.
>
> I don't really understand how to write the @state.expression the way I
> want things to happen.
> statei2a = {
> 0 : "captured",
> 1 : "registered",
> 2 : "prepared",
> }
> statea2i = dict((v, k) for k, v in statei2a.iteritems())
>
> class Device(Base):
> __tablename__ = "device"
>
> id = sa.Column(sa.Integer, primary_key=True)
> statenum = sa.Column(sa.Integer, nullable=False, default=0)
>
> def __init__(self, state):
> self.state = state
>
> @hybrid_property
> def state(self):
> return statei2a[self.statenum]
>
> @state.setter
> def state(self, state):
> self.statenum = statea2i[state]
>
> @state.expression
> def state(self):
> return statea2i[self.statenum]
You're looking to convert from int->string using a mapping in a SQL expression,
so I think you'd need to write @state.expression as a CASE statement.
from sqlalchemy import case
@state.expression
def state(self):
return case(self.statenum, statei2a)
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