A have a Machines table and a Parts table. A machine is made up of many parts,
and each part could be in many machines, so clearly this is a M:M relationship.
I've implemented this with a secondary table, which has two columns: machine_id
and part_id. There is no primary key or unique constraint on the secondary
table, just two foreign keys.
So far so good.
The problem is when I want to have 2 of a part in a machine. It was no problem
doing this:
machine = Machine('theMachine')
machine.parts.append(session.query(Part).filter_by(name =
'thePart').first())
machine.parts.append(session.query(Part).filter_by(name =
'thePart').first())
session.add(machine)
I now have two identical rows in the secondary table, which is what I want.
However, when I try to retrieve the object:
print session.query(Machine).filter_by(name = 'theMachine').first().parts
I just get:
InstrumentedList: [<Part(u'thePart')>]
The duplicates are being cut out, which is very annoying. This Stack Overflow
question<http://stackoverflow.com/questions/5656715/can-i-append-twice-the-same-object-to-an-instrumentedlist-in-sqlalchemy>
seems relevant, but I wasn't to glean any useful information from it.
How can I have duplicate entries in my M:M relationship?
Cheers,
Cam
Cameron Jackson
Engineering Intern
Air Operations
Thales Australia
Thales Australia Centre, WTC Northbank Wharf, Concourse Level,
Siddeley Street, Melbourne, VIC 3005, Australia
Tel: +61 3 8630 4591
cameron.jack...@thalesgroup.com.au<mailto:cameron.jack...@thalesgroup.com.au> |
www.thalesgroup.com.au<http://www.thalesgroup.com.au>
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