On May 19, 2011, at 5:24 PM, Faheem Mitha wrote:
>
> Unfortunately, that is not true. (So I guess just leaving the
> structure alone and switching dbs will not work.) There are 4 possible
> different database layouts. Also, there can be multiple schemas in
> each database.
So you have a model with a set of tables, the tables are split amongst multiple
schemas, say schemas A, B, and C. You then have four types of databases,
each of which have the identical set of table designs, except the actual names
of *just the schemas*, I.e. A, B, and C, randomly change.
That seems ridiculous. I would absolutely name the schemas consistently.
Or name the tables distinctly in the schemas so that search_path could be used.
Very unfortunate that PG doesn't support synonyms.
Since I know you aren't going for that, there's some other Python tricks all of
which are more complex, or interfere with how mapper() works in such a way that
I can't guarantee ongoing compatibility, than just wiping out everything with
clear mappers and re-mapping. I would keep the MetaData for each set of
tables in a dictionary and pull the appropriate set of tables out for each use,
send them into mapper(). I'd create the three copies of each Table from the
original one using table.tometadata(schema='newschema').
# runs only once
metadatas = {
'one':MetaData(),
'two':MetaData(),
'three':MetaData(),
'four':MetaData(),
}
# runs only once, per table
def table(name, *args, **kw):
t = Table(name, metadatas['one'], *args, **kw)
t.tometadata(metadatas['two'], schema='two')
t.tometadata(metadatas['three'], schema='three')
t.tometadata(metadatas['four'], schema='four')
then to map a class:
mapper(cls, metadatas['two'].tables['some_table'])
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