Event Sourcing

This contains a sample implementation to illustrate keys aspects of implementing an application that uses Event Sourcing.

Requirements

You have to have Python 3.7+ installed on your local system nad docker + docker-compose.

Setup

1. Clone this repository

2. Install the Python dependencies

In a command line - or via your IDE of choice - run

pip3 install -r requirements.txt

If you are using a virtual environment (venv) replace the pip3 with simply pip.

3. Enable docker container

docker-compose up -d

It will download and run the event store (eventstore.org). Try to access it via localhost:2113

username: admin
password: changeit

4. Initialize the database that will contain the projections

python3 setup.py

You should see an output like the one below

Ledger persistence available
Payment projection available
Decline code projection available

If you ever need to reset the projections call the same script with a -r option after setup.py.

Using

The system consists of 2 projections that should be run from command line to create projections (read models) of the system for two different purposes.

• ./src/ui/console/manage_customer_payment_projection.py

It will create a projection stored in the SQLite table payment_view. It contains only the latest status of the payment.

• ./src/ui/console/manage_decline_code_projection.py

It will create a projection stored in the SQLite table decline_view. It contains a list of all declined payments organized by the decline code, bank and date.

It also contains a helper script api.py that simulates the actions of API calls that would manipulate payments:

• create
• authorize
• settle
• refund
• decline
• find

For the full list of options you should run python3 api.py -h:

Usage: api.py [options]

Options:
  -h, --help            show this help message and exit
  -a ACTION, --action=ACTION
                        Which action to execute create, authorize, settle,
                        decline, refund or find
  -i ID, --id=ID        The payment ID to authorize, settle, decline, refund
                        or find
  -v VALUE, --value=VALUE
                        The amount to create, settle or refund
  -b BANK_NAME, --bank-name=BANK_NAME
                        The bank name
  -c DECLINE_CODE, --decline-code=DECLINE_CODE
                        The code for decline

With the exception of the find option, all the other commands, if successfully executed, will generate events that can be seen by accessing: http://localhost:2113/web/index.html#/streams/$ce-payments