Mongoengine to_python() is not working as expected

[Vishnu Jayan]

I am new to MongoDb and Python. I would like to work Field level Encryption. In order to understand the best practices, I have tried with simple to_mongo() and to_python() functions of Field class.

My code is as follows.

from mongoengine import Document, StringField

from faker import Faker

from mongoengine import connect

class TestMixin:

    pass

class TestField(StringField):

    def __init__(self, *args, **kwargs):

        super().__init__(*args, **kwargs)

    def to_mongo(self, value):

        print(f"Calling to_mongo with {value}")

        print("---------------------------")

        if value is not None:

            return f"to_mongo: {value}"

    def to_python(self, value):

        print(f"Calling to_python with {value}")

        print("---------------------------")

        # Modify the data when converting from MongoDB to Python

        if value is not None:

            modified_value = f"to_python: {value}"

            return modified_value

        return value

class MyDocument(Document):

    ssn = TestField(required=True)

    name = StringField(required=True)

    key = StringField()

if __name__ == '__main__':

    faker = Faker()

    connection = connect(host="mongodb://localhost:27017/test-db")

    my_doc = MyDocument(ssn=faker.ssn(), name=faker.name())

    try:

        print("On Saving/n-----------------")

        my_doc.save()

        print("Object saved")

    except Exception as e:

        print(str(e))

    data = MyDocument.objects

    print("ON retrieval\n-------------------")

    for item in data:

        print(f"id: {item.id}\n")

        print(f"ssn: {item.ssn}\n")

        print(f"name: {item.name}\n")

        print(f"key: {item.key}\n")

        print("-------------------")

My output is

Calling to_python with 375-07-7733
---------------------------
On Saving/n-----------------
Calling to_mongo with to_python: 375-07-7733
---------------------------
Object saved
ON retrieval
-------------------
Calling to_python with to_mongo: to_python: 066-30-4869
---------------------------
Calling to_python with to_mongo: to_python: 291-98-9774
---------------------------
Calling to_python with to_mongo: to_python: 815-65-3945

Kindly explain how this is happening and how to resolve it?