I am working on creating some tables that are versionable and what I
wanted to do was have a Composite Primary Key
where the id is the sequence and the vernum is the version number that
tracks the changes. next_version is supposed to be the max of all
version numbers for the id + 1. something along the lines of:
nodes_table = Table('nodes', metadata,
Column('id', PGBigInteger, Sequence('node_id_seq'),
primary_key=True),
Column('owner_id', Integer,
ForeignKey('users.id')),
Column('created', DateTime,
default=func.current_timestamp()),
Column('modified', DateTime,
default=func.current_timestamp(), onupdate=func.current_timestamp()),
Column('status', String(50)),
Column('type', String(50), nullable=False),
)
versionnodes_table = Table('versionnodes', metadata,
Column('id', PGBigInteger,
ForeignKey('nodes.id'), primary_key=True),
Column('vernum', Integer, primary_key=True,
default=1),
Column('modified_by_id', Integer,
ForeignKey('users.id'))
)
mapper(Node, nodes_table, polymorphic_on=nodes_table.c.type,
polymorphic_identity='Node',
properties={'childnodes':relation(Node,
secondary=node_relation_table,
primaryjoin=nodes_table.c.id==node_relation_table.c.id1,
secondaryjoin=nodes_table.c.id==node_relation_table.c.id2,
backref='parentnodes'),
'owner':relation(User)
}
)
mapper(VersionNode, versionnodes_table, inherits=Node,
polymorphic_identity='versionnode',
properties={'next_version' :
column_property(select([func.max(versionnodes_table.c.vernum)+1],
versionnodes_table.c.id==nodes_table.c.id).label('next_version')),
'modified_by' : relation(User)
}
)
what I am trying to figure out is how to set it up so that when a
change is made to a versionnode it is saved as a new record instead of
issuing an update on the current record. I have looked at using a
MapperExtension but since a before_update can't change the flush, I
don't think that will work. I also looked at a SessionExtension but I
couldn't figure out how to make those work. Any ideas would be very
helpful.
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