Simple CQRS application in Python

How it works

   X
  XXX                +------Projection------+
   X     Balance View|    Balance Sheet     |
XXXXXXX  <-----------+"XX1"-------------1400+<-------------+
   X                 |"XX2"-------------2333|              |
   X                 |                      |              |
  XXX                +----------------------+              |
 XX XX                                                     |
XX   XX  +-----------+                                     |
X     X              |Deposit                              |
                     |                                     |
   +                 |                                     |
   |                 |                                     |
   |                 |                                     |
   |                 |                                     |
   |Withdraw         v                                     |
   |                 +------Bus/Handler-----+              |
   |                 |                      |              |
   +---------------->+    Account Handler   |              |New Events
                     |                      |              |
                     +--+----------------+--+              |
                        ^                |                 |
                        |                |                 |
                        |                |                 |
            Event Stream|                |New Events       |
                        |                |                 |
                        |                |                 |
                        |                |                 |
                        |                |                 |
                        |                v                 |
                  +-----+---Event-Store--+-----+           |
                  |AccountCredited "XX1", 1000 |           |
                  |AccountCredited "XX5", 2000 |           |
                  |AccountDebited  "XX1", 300  |           |
                  |AccountCredited "XX1", 100  +-----------+
                  |AccountDebited  "XX1", 200  |
                  |AccountCredited "XX5", 333  |
                  |............................|
                  +----------------------------+

What is included

Event Store

Sample event store saves events into dictionary. Nice features:

• Saves events
• Loads event stream
• Provides events for projection

Event store does not publish events - projections need to poll for new events themselves

Account Handler

Command Handler and Command Bus as one thing for the sake of simplicity. Nice features:

• Deposits money
• Withdraws money

Balance Sheet

Projection which downloads new events from Event Store and updates balance documents. Nice features:

• Provides with balances of all the accounts
• Checks event store for update per your request

How to use it

Run app with Python 3 to perform example operations with accounts and print balances