Django Code Repetition due to Multiple objects in JSON

Question

I have the following code which works as expected i.e saves data to the db as I would like it to, however, there is a lot of code repetition and I am unable to find a way to shorten the code

I have about 30 serializers (pasting 3 to shorten the code)

class FirstOne(serializers.ModelSerializer):
    period = PeriodSerializer(many=False)

    class Meta:
        model = FirstOne
        fields = ['decimals', 'unitRef', 'value', 'period']


class SecondOne(serializers.ModelSerializer):
    period = PeriodSerializer(many=False)

    class Meta:
        model = SecondOne
        fields = ['decimals', 'unitRef', 'value', 'period']


class ThirdOne(serializers.ModelSerializer):
    period = PeriodSerializer(many=False)

    class Meta:
        model = ThirdOne
        fields = ['decimals', 'unitRef', 'value', 'period'] 

class CashFlowSerializer(serializers.ModelSerializer):
    FirstItemInJson = FirstOne(many=True)
    SecondItemInJson = SecondOne(many=True)
    ThirdItemInJson = ThirdOne(many=True)

class Meta:
    model = Basetable
    fields = "__all__"

def create(self, validated_data):
    itemOneData = validated_data.pop('FirstItemInJson')
    itemTwoData = validated_data.pop('SecondItemInJson')
    itemThreeData = validated_data.pop('ThirdItemInJson')
cashflow = Basetable.objects.create(**validated_data)
for data in itemOneData:
    period_data = data.pop("period")
    dataObj = FirstItemModelClass.objects.create(
        basetable_id=cashflow, **data)
    period_object = Period.objects.create(
        firstItem_id=dataObj, **period_data)
for data in itemTwoData:
    period_data = data.pop("period")
    dataObj = SecondItemModelClass.objects.create(
        basetable_id=cashflow, **data)
    period_object = Period.objects.create(
        secondItem_id=dataObj, **period_data)
for data in itemThreeData:
    period_data = data.pop("period")
    dataObj = ThirdItemModelClass.objects.create(
        basetable_id=cashflow, **data)
    period_object = Period.objects.create(
        thirdItem_id=dataObj, **period_data)

JSON: (trimmed to keep it shorter)

jsonToUse = {
    "CompanyId": "320193",
    "CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents": [
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "instant": "2020-09-26"
            },
            "value": "39789000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "instant": "2019-09-28"
            },
            "value": "50224000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "instant": "2018-09-29"
            },
            "value": "25913000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "instant": "2021-09-25"
            },
            "value": "35929000000"
        }
    ],
    "NetIncomeLoss": [
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2020-09-27",
                "endDate": "2021-09-25"
            },
            "value": "94680000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2019-09-29",
                "endDate": "2020-09-26"
            },
            "value": "57411000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2018-09-30",
                "endDate": "2019-09-28"
            },
            "value": "55256000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2020-09-27",
                "endDate": "2021-09-25"
            },
            "segment": {
                "dimension": "us-gaap:StatementEquityComponentsAxis",
                "value": "us-gaap:RetainedEarningsMember"
            },
            "value": "94680000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2019-09-29",
                "endDate": "2020-09-26"
            },
            "segment": {
                "dimension": "us-gaap:StatementEquityComponentsAxis",
                "value": "us-gaap:RetainedEarningsMember"
            },
            "value": "57411000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2018-09-30",
                "endDate": "2019-09-28"
            },
            "segment": {
                "dimension": "us-gaap:StatementEquityComponentsAxis",
                "value": "us-gaap:RetainedEarningsMember"
            },
            "value": "55256000000"
        }
    ],
    "DepreciationDepletionAndAmortization": [
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2020-09-27",
                "endDate": "2021-09-25"
            },
            "value": "11284000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2019-09-29",
                "endDate": "2020-09-26"
            },
            "value": "11056000000"
        },
        {
            "decimals": "-6",
            "unitRef": "usd",
            "period": {
                "startDate": "2018-09-30",
                "endDate": "2019-09-28"
            },
            "value": "12547000000"
        }
    ]}

Given I have 30 items in my JSON, currently I am going through each item using a for loop so that I can store the Period data in that. How can I shorten my code?

Thank you for your time and help.

Answer 1

I'm not well-versed in Django, considering all the magic it does behind the scenes using metaproramming, and I don't have an environment where I could test the code I'll present, but I'll try to give a couple advices:

---

Firstly, you may try creating serializers.ModelSerializer-inheriting classes using a factory.

Write a function that creates the classes and call it like this:

def model_serializer_factory(meta_model, meta_fields):

    class T(serializers.ModelSerializer):
        period = PeriodSerializer(many=False)

        class Meta:
            model = meta_model
            fields = meta_fields

    return T


FirstOneSerializer, SecondOneSerializer, ThirdOneSerializer = (
    model_serializer_factory(model, ['decimals', 'unitRef', 'value', 'period'])
    for model in (FirstOne, SecondOne, ThirdOne)
)

This is a (very) simplified example that's specific to the code you've provided. If your classes have more complex structures, you could create them on the fly using type like this:

def create_serializer_class(meta_model, meta_attrs, serializer_name, serializer_attrs):
    meta = type(
        'Meta',
        (),
        {'model': meta_model, **meta_attrs}
    )

    return type(
        serializer_name,
        (serializers.ModelSerializer,),
        {**serializer_attrs, 'Meta': meta}
    )


FirstOneSerializer, SecondOneSerializer, ThirdOneSerializer = (
    model_serializer_factory(
        model,
        {'fields': ['decimals', 'unitRef', 'value', 'period']},
        serializer_name,
        {'period': PeriodSerializer(many=False)}
    )
    for model, serializer_name in (
        (FirstOne, 'FirstOneSerializer'),
        (SecondOne, 'SecondOneSerializer'),
        (ThirdOne, 'ThirdOneSerializer')
    )
)

I'm simply creating serializers in a loop since they're (almost) identical in your example, but you can create arbitrary classes using this improved model_serializer_factory function.

Refer to this question which is about the exact same thing as I'm explaining here.

---

Secondly, your copy-pasted loops at the end can be parameterized as well. Turning item_X_Data and X_ItemModelClass into loop variables is trivial. For passing the X_Item_id as a kwarg to Period.objects.create, you'll have to convert it into a single-item dictionary and use kwargs-spreading, though.

parameterized_list = [
    (itemOneData, FirstItemModelClass, 'firstItem_id'),
    (itemTwoData, SecondItemModelClass, 'secondItem_id'),
    (itemThreeData, ThirdItemModelClass, 'thirdItem_id')
]

for data_list, model, item_id in parameterized_list:
    for data in data_list:
        period_data = data.pop("period")
        dataObj = model.objects.create(basetable_id=cashflow, **data)
        period_object = Period.objects.create(**{item_id: dataObj}, **period_data)