Given the three mappings *First*, *Second* and *Partitioned*, I want to
declare a relationship between *First* and *Partitioned*. The problem is
that *Partitioned* is partitioned by partition_key which is a column in
*First* but not in *Second*. *Second* however contains the identifier that
actually links *First* to specific rows in the partitioned table.
So far the mapping looks like this mock example:
partitioned = relationship("Partitioned",
secondary=Base.metadata.tables['schema.seconds'],
primaryjoin="and_(First.first_id==Second.first_id,
First.partition_key==Partitioned.partition_key)",
secondaryjoin="Second.other_id==Partitioned.other_id",
foreign_keys="[Second.first_id, Partitioned.partition_key,
Partitioned.other_id]",
uselist=True, innerjoin=True, lazy='dynamic')
It works, but it only interpolates the First.first_id with the actual value
which normally makes sense but to make the PostgreSQL constraint-exclusion
work the First.partition_key would need to be interpolated with the proper
value as well. Right now it is only given as
First.partition_key==Partitioned.partition_key.
Does that make sense? I am not sure if my relationship configuration is
wrong or if this kind of mapping is simply not supported.
On Thu, Dec 5, 2013 at 3:31 PM, Michael Bayer <mike...@zzzcomputing.com>wrote:
>
> On Dec 5, 2013, at 6:57 AM, Adrian Schreyer <adrian.schre...@gmail.com>
> wrote:
>
> Actually that was a bit too early but I tracked the problem down to the
> many-to-many relationship. Parameters are only interpolated (e.g.
> %(param_1)s) for the primaryjoin to the secondary table. Is there a
> technique to force relationship() to interpolate a parameter between the
> 1st and 3rd table instead of using only table.column=table.column?
>
>
> there’s no reason why that would be the case can you provide more
> specifics?
>
>
>
>
>
>
> On Thu, Dec 5, 2013 at 10:58 AM, Adrian Schreyer <
> adrian.schre...@gmail.com> wrote:
>
>> Never mind,
>>
>> the problem was that I specified the clause in a secondaryjoin and not in
>> the primaryjoin of the relationship().
>>
>>
>> On Thu, Dec 5, 2013 at 10:44 AM, Adrian <adrian.schre...@gmail.com>wrote:
>>
>>> Hi All,
>>>
>>> I have a few partitioned tables in my PostgreSQL database but I do not
>>> know yet how to make the ORM relationship() with partition
>>> constraint-exclusion<http://www.postgresql.org/docs/9.3/static/ddl-partitioning.html#DDL-PARTITIONING-CONSTRAINT-EXCLUSION>
>>> on
>>> the instance level. Constraint-exclusion does not work with joins and
>>> requires scalar values - the problem is that I would need to add an
>>> additional WHERE clause to the primaryjoin (which adds the partition key)
>>> if the relationship is accessed from the* instance level*, e.g.
>>> user.addresses. Is there a mechanism in relationship() to distinguish
>>> between class-based joins (User.addresses) and instance-level access?
>>>
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>>
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