When a customer purchases an item using their payment card at a store, several things happen in the background. Below diagram shows the typical entities in the payment card industry with an example transaction from a Cardholder to a Merchant.
Project: Build a Database and API's for a fintech company that acts as an Issuer. Fintech opperates with its customers(cardholders) and Scheme
- Django application (written in python, following PEP8 and PEP257 conventions)
- Django rest_framework for API's
- This application is connected to Postgresql 10 database, is scalable and robust for this purpose.
Follow the below steps to get the application running:
Create database in the Postgresql instance. Reccomended to create a database with application name. Eg: fintech_api
Please note that below environment variables need to be configured in .bash_profile before attempting to start the application server and running management commands.
FINTECH_SECRET_KEY - secret key for the application
DB_NAME - name of the database in postgresql, usually it is your app name.
DB_USER - username of the database in Postgresql
DB_PASS - password of the database in Postgresql
DB_HOST - 127.0.0.1 for localhost
DB_PORT - usually it is 5432 or 5433 depending on what you choose
- go to working directory
- create a virtualenv
- activate virtualenv
pip3 install -r requirements.txtthis will install needed dependencies in the virtual environment
To migrate models to database tables, Run the following command:
python manage.py makemigrations
python manage.py migrate
To create superuser, Run the following command:
python manage.py createsuperuser
create username and password --> Login to admin --> add 2 Customers in Customer table by providing needed details ---> add Accounts for these 2 Customers in Accounts table matching the details in Customer table. (Note: total_balance and available_balance values should be the same since both values are equal before authorization and presentation)
We added dummy customers inorder to test our API Request.
To start the server, Run the following management command:
python manage.py runserver
server will run at: http://127.0.0.1:8000/
This command is to credit amount to cardholder. Run it as follows:
python manage.py load_money <cardholder_id> <amount> <currency>
Format to be:
cardholder_id - numerical value representing the ID of the cardholder to credit. Eg: 21321
amount - float value, with 2 decimal places, representing the amount of money to credit. Eg: 1000.50
currency - 3 (capital) letter value, representing the currency of the account to credit. Eg: EUR
Example command:
python manage.py load_money 21321 1000.50 EUR
This command is used to run the batch process of settling transactions to the Scheme.
python manage.py batch_process
4 tables used: Customers, Accounts, Transactions and Transfers. The following Entity Relation diagram illustrates how I intend to implement the database:
This feature is used by the Scheme in order to send authorisation/presentment WebHooks.
For authorisation requests, below parameters in form of JSON data need to be available in the request:
{
"type": "authorisation",
"card_id": "21321",
"transaction_id": "1234ROKKA",
"merchant_name": "SNEAKERS R US",
"merchant_country": "US",
"merchant_mcc": "5139",
"billing_amount": "90.00",
"billing_currency": "EUR",
"transaction_amount": "100.00",
"transaction_currency": "USD"
}
For presentment requests, below parameters in form of JSON data need to be available in the request:
{
"type": "presentment",
"card_id": "21321",
"transaction_id": "1234ROKKA",
"merchant_name": "SNEAKERS R US",
"merchant_country": "US",
"merchant_city": "LOS ANGELES",
"merchant_mcc": "5139",
"billing_amount": "90.00",
"billing_currency": "EUR",
"transaction_amount": "100.00",
"transaction_currency": "USD",
"settlement_amount": "89.50",
"settlement_currency": "EUR"
}
This feature is used by Cardholders to see their presented transactions.
The following query parameters need to be set in order to get data:
cardholder - numerical value
start_date - datetime format %Y-%m-%d %H:%M:%S
end_date - datetime format %Y-%m-%d %H:%M:%S
Example request
http://localhost:8000/transactions/?cardholder=21321&start_date=2018-10-21 00:00&end_date=2018-10-22 03:50
Returns data is a JSON containing all specific transactions in that timeframe.
Functionality here is used by Cardholders, in order to see their current accounts and balances.
The following query parameters need to be set in order to get data:
cardholder - numerical value
type - ledger or available
Example request
http://localhost:8000/balances/?cardholder=21321&type='ledger'
Return data is a JSON containing current balance(presented) or available balance.