On Fri, Feb 23, 2018 at 10:29 PM, <jens.troe...@gmail.com> wrote:
> Hi,
>
> I’d like to follow up on the Backref Arguments example from the
> documentation.
>
> First, to make sure I understand this correctly, are these two lines
> equivalent? I would assume so, considering this comment: “By default, this
> value [primaryjoin] is computed based on the foreign key relationships of
> the parent and child tables (or association table).”
>
> addresses = relationship("Address",
> backref="user")
>
> # Is like saying…
>
> addresses = relationship("Address",
> primaryjoin="User.id==Address.user_id",
> backref="user")
they are equivalent assuming that's the natural primaryjoin condition
that would be derived from the two mapped tables, sure.
>
> Now for the backref with an argument. In the example, the email’s local part
> `tony` is hardcoded. Is there a way to parameterize that local part
> elegantly (i.e. pass arguments to that relationship), or is the following
> function the recommended way to go:
>
> def user_addresses(self, name):
> return [a for a in self.addresses if a.email.startswith(name)]
there's a recipe at
https://bitbucket.org/zzzeek/sqlalchemy/wiki/UsageRecipes/GlobalFilter.
If you have a very small number of addresses, then the in-Python
filtering option is fine. other options are dynamic relationship
(http://docs.sqlalchemy.org/en/latest/orm/collections.html#dynamic-relationship)
and using object_session
(http://docs.sqlalchemy.org/en/latest/orm/join_conditions.html#building-query-enabled-properties)
>
> Thanks!
> Jens
>
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> SQLAlchemy -
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