Event sourcing pattern in Microservices - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the main storage in event sourcing.

Microservices

events = []  # This list stores all [1]

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Astates

Blogs

Cevents

Dsnapshots

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing events with snapshots or current states.

Using logs as a generic term instead of events.

In event sourcing, all changes are stored as events in an append-only log.

2fill in blank

medium

Complete the code to rebuild the current state from events.

Microservices

state = initial_state
for event in events:
    state = [1](state, event)

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Aapply_event

Bsave_event

Cdelete_event

Dlog_event

Attempts:

3 left

💡 Hint

Common Mistakes

Using functions that do not modify the state.

Confusing event application with event storage.

The apply_event function updates the state by applying each event in order.

3fill in blank

hard

Fix the error in the event storage function to append new events.

Microservices

def store_event(event):
    [1].append(event)

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Astate

Bevents

Csnapshot

Dlog

Attempts:

3 left

💡 Hint

Common Mistakes

Appending events to the wrong variable.

Using a variable that does not exist.

New events must be appended to the events list to keep the event history.

4fill in blank

hard

Fill both blanks to create a snapshot after every 100 events.

Microservices

if len(events) [1] 100 == 0:
    snapshot = [2](state)

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A%

B==

C>

Dcreate_snapshot

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators.

Confusing snapshot creation with event storage.

The modulo operator % checks if 100 events have occurred, then create_snapshot saves the current state.

5fill in blank

hard

Fill both blanks to implement event replay with snapshot optimization.

Microservices

def rebuild_state():
    state = [1]
    for event in events[[2]:]:
        state = apply_event(state, event)  # Apply remaining events
    return state  # Return the latest state

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Asnapshot

B0

Clen(snapshot_events)

Dinitial_state

Attempts:

3 left

💡 Hint

Common Mistakes

Starting replay from the beginning every time.

Ignoring snapshots and replaying all events.

Start from the latest snapshot, replay events after the snapshot index len(snapshot_events).