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**Event Sourcing** is an architectural approach in which the system does not store an object's current state directly, but stores **all the events that led to it**.

### The essence

Every data change is recorded as an event:

> "Order created", "Item added", "Payment received".

To get the current state, the system simply replays all the events in order.
This way, the database becomes a history log rather than a snapshot of the current state.

### Example

The usual approach stores:

```javascript
Order: {id: 1, status: "paid"}
```

Event Sourcing stores:

```javascript
1. OrderCreated
2. ItemAdded
3. PaymentReceived
```

From these events, the order's current state can be recomputed at any moment.

### Why this is needed

- **Full history of changes:** convenient for auditing and analytics.
- **Easy rollback and state replay.**
- **Natural integration with event-driven architecture (EDA).**
- **Flexibility:** data can be recomputed if the business rules change.

### Drawbacks

- Makes storing and reading data harder (you need "projections" for fast queries).
- Harder to implement transactional integrity.

**Summary:**

> **Event Sourcing** is a way of storing not the result but the **history of events**,
> letting you precisely restore the past and flexibly manage the system's state.

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