On May 2, 2007, at 3:53 PM, askel wrote:
>
> Michael,
>
> Thank you for answering. The following is what I tried in order to
> follow your advise:
>
> account_summaries = select(
> [
> transactions.c.account_id,
> func.max(transactions.c.processed_at).label('last_used'),
> func.count(transactions.c.id).label('times_used'),
> ],
> group_by=[transactions.c.account_id],
> ).alias('account_summaries')
>
> class AccountSummary(object):
> pass
>
> account_summary_mapper = mapper(Account, account_summaries,
> non_primary=True)
>
> account_mapper = mapper(Account, accounts,
> properties={
> 'summary': relation(AccountSummary, lazy=True, viewonly=True,
> primaryjoin=(accounts.c.id==account_summary.c.account_id)),
> },
> )
>
> But it raises the following exception when I try to instantiate
> Account class:
>
> ArgumentError: Could not assemble any primary key columns for mapped
> table 'account_summary'
>
> What am I doing wrong?
transactions.account_id needs to be a primary_key column, or
otherwise add a primary_key=[transactions.account_id] attribute to
mapper().
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