Fix ModelReceipt queries #4432
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Fix ModelReceipt queries #4432
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Hybrid properties were the root cause of performance issues with various queries we were trying to run on model receipts. Now we return an SQL aggregate function instead, allowing you to build similar queries without the massive performance hit. This change uses the attendee receipt discrepancies and nonzero balance pages as a proof of concept -- if these become useable once on prod, then we can apply this change to related currently-unusable pages. One important thing to note is that you should NOT ever use the new _sql aggregate functions from two different tables in one query -- this either creates a cartesian join or, if you specify joins, repeats the rows from earlier tables in the join and screws up calculations (e.g., doubling the item total). You can see how we handle needing aggregates from two different tables in the attendees_nonzero_balance page handler, where we create a subquery for the ReceiptItems table. This appears to work well alongside normal aggregate functions/outer joins for ReceiptTransactions. For more information, see https://stackoverflow.com/questions/12484975/sqlalchemy-using-func-with-outerjoin-on-multiple-tables and https://blog.miguelgrinberg.com/post/nested-queries-with-sqlalchemy-orm
We were accidentally selecting only discrepant receipts when you had include_discrepancies off, whoops.
These were the only pages that relied on the .is_paid hybrid property, which I took out.
This will let us add items to attendee receipts for purchases that don't affect their default cost without tripping the receipt discrepancies page. The FK stands for Foreign Key.
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Hybrid properties were the root cause of performance issues with various queries we were trying to run on model receipts. Now we return an SQL aggregate function instead, allowing you to build similar queries without the massive performance hit. This change uses the attendee receipt discrepancies and nonzero balance pages as a proof of concept -- if these become useable once on prod, then we can apply this change to related currently-unusable pages.
One important thing to note is that you should NOT ever use the new _sql aggregate functions from two different tables in one query -- this either creates a cartesian join or, if you specify joins, repeats the rows from earlier tables in the join and screws up calculations (e.g., doubling the item total). You can see how we handle needing aggregates from two different tables in the attendees_nonzero_balance page handler, where we create a subquery for the ReceiptItems table. This appears to work well alongside normal aggregate functions/outer joins for ReceiptTransactions.
For more information, see https://stackoverflow.com/questions/12484975/sqlalchemy-using-func-with-outerjoin-on-multiple-tables and https://blog.miguelgrinberg.com/post/nested-queries-with-sqlalchemy-orm