Struggling to return partial data from multiple models connected via a "manyToMany" field and "through" relationship

[proffalken]

Hi,

I've built https://github.com/MakeMonmouth/mventory around this and it's awesome, but as I start to get more advanced I'm running in to issues.

In my models I want to link Components to Suppliers. Due to the nature of the Components, each Component may be sourced from multiple Suppliers at different prices, and each Supplier can provide multiple Components.

As a result, I've created a new model to link Supplier and Component, and now I want to display this in the API.

The issue I have is that whilst I want this data to be shown as part of the call for a Component, I only want certain fields to be returned.

The code I have so far is as follows:

class ComponentSerializer(serializers.HyperlinkedModelSerializer):
    component_prices = serializers.SerializerMethodField()

    def get_component_prices(self, obj):
        prices = []

        for supplier in obj.supplier_options.all():
            details = {}
            details['supplier'] = supplier.name
            cs_details = ComponentSupplier.objects.get(supplier=supplier, component=obj)
            details['price'] = cs_details.members_price
            details['currency'] = cs_details.currency
            details['included_donation_amount'] = cs_details.members_price - cs_details.bought_at
            prices.append(details)

        return prices

    class Meta:
        model = Component
        fields = ['url', 'name', 'sku', 'mpn', 'upc', 'storage_bin','measurement_unit', 'qty', 'component_prices']
        depth = 4

This gives me the following output for a test component:

HTTP 200 OK
Allow: GET, POST, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

[
    {
        "url": "http://localhost:8180/rest/components/1/?format=api",
        "name": "Test 1",
        "sku": "tst-1",
        "mpn": null,
        "upc": null,
        "octopart_data": {},
        "storage_bin": [
            {
                "url": "http://localhost:8180/rest/storage_bins/1/?format=api",
                "name": "Bin 01",
                "short_code": null,
                "unit_row": null,
                "unit_column": null,
                "storage_unit": {
                    "url": "http://localhost:8180/rest/storage_units/1/?format=api",
                    "name": "Cupboard 01",
                    "short_code": null,
                    "room": {
                        "url": "http://localhost:8180/rest/rooms/1/?format=api",
                        "name": "Main room",
                        "short_code": null,
                        "building": {
                            "url": "http://localhost:8180/rest/buildings/1/?format=api",
                            "name": "Old Shop",
                            "address": null,
                            "postcode": null
                        }
                    }
                }
            }
        ],
        "measurement_unit": {
            "url": "http://localhost:8180/rest/component_measurements/1/?format=api",
            "unit_name": "ea",
            "unit_description": "each"
        },
        "qty": 3,
        "component_prices": [
            {
                "supplier": "PiMoRoNi",
                "price": 49.5,
                "currency": "GBP",
                "included_donation_amount": 4.5
            }
        ]
    }
]

Ideally, I'd also want to include a link for each of the Supplier items to their specific view in the API, but I'm struggling to work out how I do this without returning all of the fields in the ComponentSupplier model (I don't want to disclose how much a Component is purchased for or what the markup might be, but I do want to disclose how much the membership price differs from the RRP for example).

I'm reasonably sure that I need to follow the second example in this section of the docs, but I can't quite work out what the values should be in order to retrieve only the data about the Supplier currently being examined in the "main" loop.

Thanks in advance for any light you can shed on this!