Make updating converted prices more robust #92

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lukas · 2025-03-22T16:05:19Z

lukas commented

2025-03-22 16:05:19 +00:00

Right now the code is quite fragile:

First it's manually checked in Purchase model's save() method if the converted price or currency is different, if it is, it sets both to default.
It's checked in the convert_prices method, and this uses the same way as in the save() method, which means code duplication.
calculate_price_per_game also depends on this and is itself very hacky way of determining if an update is needed. It does this by directly querying Django-Q's table Tasks and comparing its last run timestamp with the updated_at field of Purchase model.

Solutions

Either add a needs_price_update field to Purchase which would be reset in the model's save method. Being boolean it's unlikely to ever change, and the brittle check in convert_prices would just check the value of this field.
This would also be re-used for calculate_price_per_game because if a price has changed we also need to recalculate this.

Right now the code is quite fragile: 1. First it's manually checked in Purchase model's `save()` method if the converted price or currency is different, if it is, it sets both to default. 2. It's checked in the `convert_prices` method, and this uses the same way as in the `save()` method, which means code duplication. 3. `calculate_price_per_game` also depends on this and is itself very hacky way of determining if an update is needed. It does this by directly querying Django-Q's table `Tasks` and comparing its last run timestamp with the `updated_at` field of Purchase model. # Solutions 1. Either add a `needs_price_update` field to Purchase which would be reset in the model's save method. Being boolean it's unlikely to ever change, and the brittle check in `convert_prices` would just check the value of this field. 2. This would also be re-used for `calculate_price_per_game` because if a price has changed we also need to recalculate this.

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Reference: lukas/timetracker#92