Peewee 别名不起作用并抛出 AttributeError

Question

I have a Order model and Payment model. Payment model has a jsonb column data .

My Query:

orders = (
          Order
          .select(Order, Payment.data.alias('payment_data'))
          .join(Payment, JOIN_LEFT_OUTER, on=(Order.payment==Payment.id))
          .iterator()
         )

When I am iterating over the above query, and accessing order.payment_data , I am getting an AttributeError

But if I write the query below, it gives me the payment_data key in the dict while iterating over the orders:

orders = (
          Order
          .select(Order, Payment.data.alias('payment_data'))
          .join(Payment, JOIN_LEFT_OUTER, on=(Order.payment==Payment.id))
          .dicts()
          .iterator()
         )

Can someone please explain me what I am doing wrong in the first query and how can have access to order.payment_data ?

Thanks

Answer 1

When I am iterating over the above query, and accessing order.payment_data, I am getting an AttributeError

The payment data is probably getting attached to the related payment instance. So instead of order.payment_data you would look up the value using:

order.payment.payment_data

If you want all attributes simply patched directly onto the order, use the objects() query method, which skips the model/relation graph:

orders = (Order
          .select(Order, Payment.data.alias('payment_data'))
          .join(Payment, JOIN_LEFT_OUTER, on=(Order.payment==Payment.id))
          .objects()  # Do not make object-graph
          .iterator())
for order in orders:
    print(order.id, order.payment_data)

This is all covered in the docs: http://docs.peewee-orm.com/en/latest/peewee/relationships.html#selecting-from-multiple-sources

Answer 2

This could be a result of having NULL fields in joined results. Probably you miss payment_data for some records and peewee doesn't handle this situation as expected.

Check if your query results contain NULL s in places of payment_data . If so you should probably check if order has payment_data attribute on each iteration.

Here is more detailed explanation on Github: https://github.com/coleifer/peewee/issues/1756#issuecomment-430399189