Dear list,
I'm still working on a DNS administration web interface and have to deal
with DNS records. This is what I have so far:
-------------------------------------------------------------------------------
import sqlalchemy as sql
import sqlalchemy.orm as orm
from sqlalchemy.databases.postgres import PGInet
records_table = sql.Table(
'records', metadata,
sql.Column('id', sql.Integer, primary_key=True),
sql.Column('name', sql.Unicode(80)),
sql.Column('type', sql.Unicode(10)),
sql.Column('content', sql.Unicode(200)),
sql.Column('inet', PGInet),
)
class Record(MyOrm):
@property
def ptr_records(self):
"""
Returns matching PTR records for an A record
"""
assert self.type=='A'
assert self.inet!=None
return Record.q().filter_by(type='PTR', inet=self.inet)
orm.mapper(Record, records_table)
-------------------------------------------------------------------------------
So for an address (A) entry I'd like to find out if there is a matching
PTR record. Match criteria are the "inet" column. So if I have a certain
A record...
a = query(Record).filter_by(type='A').one()
...and like to find out the matching PTR records I would call...
ptr = a.ptr_records
This works okay so far. But somehow it feels wrong to do queries in
properties I add to the Record class. Especially since the ptr_records
do not get cached and the query is run every time I access this
property. So I wondered how to do that as properties of the mapper. I
started with
http://www.sqlalchemy.org/docs/04/mappers.html#advdatamapping_relation_customjoin
But that example deals with User and Address tables and not with
self-references. I suspect I have to alias the table. Roughly I'm
thinking of something like:
properties={
'ptr_records': relation(Record, primaryjoin=and_(
records_table.c.type=='PTR',
records_table.c.inet=records_table2.c.inet
))
}
I don't know how to say "match other Record objects where the 'inet'
column contains the same value". How do I do that correctly?
Cheers
Christoph
P.S.: I simplified the models for this posting so bear with me if this
is not code that would run as is.
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