Deal with the change of field data type of PynamoDB, an ORM of DynamoDB - Best Software Development Team Extension Partner for Nordics

Effectively manage the change of field data type of PynamoDB, an object-relational mapper (ORM) for DynamoDB. Ensure smooth database schema updates and maintain application performance and integrity with this guide.

PynamoDB, with a Python interface, is a great ORM for AWS DynamoDB. DynamoDB is a NoSQL database with scalability and security and it has awesome API and SDKs. PynamoDB wraps the underneath APIs of DynamoDB and gives a beautiful pythonic way to use DynamoDB.

In real-world our DB fields are not constant. It can change with the requirements update of our project. The hard part is when you have to maintain the old and new features. For example, a field data type can change from String to Binary. So if any API e.g. REST API with versioning is working with DynamoDB, you have to accept both old data type (String) and new data type (Binary). We are going to find a solution in such a case.

Setting the goal

Let’s start with setting a goal. Assume we have a field with Dynamo data type List. But after times it changes to Map. So we will do

• Accept Map object and save to DynamoDB
• Accept List object and change it to Map according to requirement and save to DynamoDB as our field changed to Map
• Return Map object according to requirement change

Setting the project

Let’s add a couple of files to do our task.

# Add project folder
mkdir change-field-ddb
cd change-field-ddb
# Add Pipfile for requirements mange with pipenv
touch Pipfile
# For Custom PynamoDB attributes
touch attributes.py
# Add models.py to add pynamo model
touch models.py
# To test everything
touch test.py

Add python requirements

Add following requirements to Pipfile

[dev-packages]
pipenv = "==2020.8.13"
moto = "==1.3.14"
[packages]
pynamodb = "==4.3.2"
[requires]
python_version = "3.8"

Now initiate pipenv with

pipenv install

Now the project will look like

tree
.
├── attributes.py
├── models.py
├── Pipfile
├── Pipfile.lock
└── test.py

The changed datatype

Let’s assume our previous datatype (List) for a field result is

[3.75, 3.17, 3.90, 3.67, .......]

So the result stores CGPA of a student from 1st semester to final semester e.g. result[0] as 1st semester, result[1] as 2nd semester, and so on. But we will make it better (Map) at the updated version

{
    'semester 1': 3.75,
    'semester 2': 3.17,
    'semester 3': 3.90,
    'semester 4': 3.67,
    ..................
}

PynamoDB attributes

Add the custom PynamoDB attribute to accept old (List) and new (Map) attribute and saves only as Map. But at return time it will return old (List) data as Map and also new data as Map. Also, we are going to use custom UUIDAttribute which will be used as a hash key.