Updating line item quantity doesn't recalculate discounts about django-oscar-api HOT 7 CLOSED

Hi @ckepper. Discounts are calculated by applying offers on the complete basket, not just per line. So this is a bit of an edge-case as we follow the way oscar caclulates the discounts on a basket.

Do you mean btw that price_excl_tax and price_excl_tax_excl_discounts are not automatic recalculated on your client when not retrieving the basket again? These fields are only available in the basket right?

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I am aware that this might be an edge case and I know that Oscar calculates discounts on the basket and not on a single line item.

What I found confusing was that I received a response to the PUT request that included price_excl_tax_excl_discounts but the value was incorrect. I would have expected that the response shows either the correct value (with discount applied) or no discount field at all. Hope that makes sense.

Here is the output of the PUT request. As you can see, price_excl_tax == price_incl_tax_excl_discounts:

{
  "url": "https://localhost/shop/api/v1/baskets/37/lines/31/",
  "product": "https://localhost/shop/api/v1/products/8/",
  "quantity": 100,
  "attributes": [],
  "price_currency": "USD",
  "price_excl_tax": 299,
  "price_incl_tax": 299,
  "price_incl_tax_excl_discounts": 299,
  "price_excl_tax_excl_discounts": 299,
  "is_tax_known": false,
  "warning": null,
  "basket": "https://localhost/shop/api/v1/baskets/37/",
  "stockrecord": "https://localhost/shop/api/v1/stockrecords/8/",
  "date_created": "2016-11-13T00:17:06.447193Z"
}

The call to the basket lines however reveals that there is a discount on the product (price_excl_tax != price_incl_tax_excl_discounts):

{
  "count": 1,
  "next": null,
  "previous": null,
  "results": [
    {
      "url": "https://localhost/shop/api/v1/baskets/37/lines/31/",
      "product": "https://localhost/shop/api/v1/products/8/",
      "quantity": 100,
      "attributes": [],
      "price_currency": "USD",
      "price_excl_tax": 269.1,
      "price_incl_tax": 269.1,
      "price_incl_tax_excl_discounts": 299,
      "price_excl_tax_excl_discounts": 299,
      "is_tax_known": false,
      "warning": null,
      "basket": "https://localhost/shop/api/v1/baskets/37/",
      "stockrecord": "https://localhost/shop/api/v1/stockrecords/8/",
      "date_created": "2016-11-13T00:17:06.447193Z"
    }
  ]
}

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@ckepper Ah ok, I see now that the price_excl_tax_excl_discounts is also serialized in the line response (which means that we don't apply the offers to the basket before the response). This should be fixed (or we should leave out the price_incl_tax_excl_discounts and price_excl_tax_excl_discounts fields). I'll investigate this further and will come up with a proper solution. Thanks for reporting!

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I will try to fix this (when I have more time) in a proper way. In the meanwhile I have this branch which hopefully fixes this : https://github.com/django-oscar/django-oscar-api/tree/fix/update-line-quantity Can I ask you try this (just to see if I'm lucky :) )

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Thank you for supplying this patch so quickly. I tried it out but unfortunately it didn't fix it. I stepped through the code with a debugger and found that the correct value was in the result cache (basket._lines._result_cache[0]) but this was not used for the output.

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Hi @ckepper, I think I fixed this in https://github.com/django-oscar/django-oscar-api/tree/fix/update-line-quantity now (and I added a test for it). Can you confirm this works for you? Then I'll review it next week and make a new release of oscarapi. Thnx.

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@ckepper, We already made a proper solution for this and merged this to master. Maybe you can check this so we are sure we have the correct solution?

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