CRUD stores only current state, losing history. Event‑Sourcing records every change as an immutable event, enabling you to answer "How did we get here?"

Growing Marijuana with Event‑Sourcing — Introduction

The story of `myPlant`

Three months ago I planted a marijuana seed in a small pot. I named it myPlant and put it near the window. The first week was exciting — I watered it daily, watched the first leaves sprout, and took photos to track its growth.

Then life got busy. Work deadlines piled up, I traveled for a week, and I forgot a few times — you know how it goes. I still watered myPlant when I remembered, but the intervals became irregular: two weeks would pass, then I’d water it twice in one week, then another long gap.

Today I checked on `myPlant`. The leaves are yellowing, the stem is thin, barely 15 cm tall. Something went wrong, but I can't remember what. Did I water it enough? I honestly can't recall.

Meanwhile, Grandma's plant — same day, same strain — stands at 45 cm with lush green leaves. While I'm trying to remember *if* I watered mine, hers looks ready for a photoshoot.

CRUD: the traditional approach

| id            | height | health | lastWatered         | trimCount |
|---------------|--------|--------|---------------------|-----------|
| myPlant       | 15     | 30     | 2023-10-15T14:30:00 | 0         |

| id            | height | health | lastWatered         | trimCount |
|---------------|--------|--------|---------------------|-----------|
| grandmasPlant | 45     | 95     | 2023-10-30T08:45:00 | 12        |

Both plants are stored as simple rows in a CRUD database, showing only their current state.

The question CRUD cannot answer

Why is myPlant unhealthy while Grandma's plant thrives?

I can see myPlant is in poor condition, but I cannot answer:

Was it watered consistently or sporadically?
How many times was it watered in total?
Were there long gaps between watering sessions?
Did the health ever improve and then decline again?

With CRUD, I only have a snapshot of myPlant’s current state. The history is gone—overwritten with each update. I can’t debug the problem because I don’t know how myPlant got to this state.

Grandma's secret

"How do you do it, Grandma?" I asked.

She smiled and pulled out a small notebook. "I keep track of everything," she said. "Every time I water it, trim it, or do anything — I write it down with the date"

Her notebook looked like this:

2023-08-01T10:00:00: Seeded
2023-08-03T08:30:00: Watered
2023-08-06T09:15:00: Watered
2023-08-09T07:45:00: Watered
2023-08-12T08:00:00: Watered
2023-08-15T09:30:00: Watered, Trimmed
2023-08-18T08:15:00: Watered
...
2023-10-28T07:30:00: Watered
2023-10-30T08:45:00: Watered

But why does this make a difference?

Looking at her notebook I could immediately see the pattern: consistent watering every 2–3 days. My CRUD snapshot couldn’t tell me that. It only showed the last time I watered myPlant, not the pattern of care.

Grandma’s notebook is Event‑Sourcing — tracking every event that happened, not just the current state.

Event‑Sourcing: storing the full history

With Event‑Sourcing, instead of storing only the current state, we store every event that happened:

type PlantEvent =
  | {
      type: "Seeded";
      plantId: string;
      occured_at: Date;
    }
  | { type: "Watered"; plantId: string; occured_at: Date }
  | { type: "Trimmed"; plantId: string; occured_at: Date }
  | { type: "Died"; plantId: string; occured_at: Date };

myPlant.ts (sporadic care)

const myPlantEvents: PlantEvent[] = [
  { type: "Seeded", plantId: "myPlant", occured_at: new Date("2023-08-01T10:00:00") },
  { type: "Watered", plantId: "myPlant", occured_at: new Date("2023-08-03T08:30:00") },
  { type: "Watered", plantId: "myPlant", occured_at: new Date("2023-08-20T09:15:00") },
  { type: "Died", plantId: "myPlant", occured_at: new Date("2023-10-15T14:30:00") },
];

grandmasPlant.ts (consistent care)

const grandmasPlantEvents: PlantEvent[] = [
  { type: "Seeded", plantId: "grandmasPlant", occured_at: new Date("2023-08-01T10:00:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-02T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-03T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-04T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-05T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-06T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-07T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-08T08:30:00") },
  { type: "Trimmed", plantId: "grandmasPlant", occured_at: new Date("2023-08-09T09:00:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-09T09:15:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-10T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-11T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-12T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-13T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-14T08:30:00") },
  { type: "Trimmed", plantId: "grandmasPlant", occured_at: new Date("2023-08-15T09:00:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-15T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-16T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-17T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-18T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-19T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-20T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-21T08:30:00") },
  { type: "Trimmed", plantId: "grandmasPlant", occured_at: new Date("2023-08-22T09:00:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-22T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-23T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-24T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-25T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-26T08:30:00") },
  { type: "Trimmed", plantId: "grandmasPlant", occured_at: new Date("2023-08-27T09:00:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-27T08:30:00") },
  { type: "Watered", plantId: "grandmasPlant", occured_at: new Date("2023-08-28T08:30:00") },
];

The insight: now we can answer the question. myPlant was watered only twice in the first 19 days before it died from neglect; Grandma’s plant was watered regularly and trimmed twice per week. The events tell the complete story of how we got to the current state — my neglect led to death, while consistent care produced healthy growth.

Summary

Event‑Sourcing provides a fundamentally different approach to managing state:

CRUD stores only the current state → loses history
Event‑Sourcing stores all events → a complete audit trail; can answer “How did we get here?”

Storing events (Seeded, Watered, Trimmed, Died) lets us:

Answer questions that CRUD cannot (for example, "Why did myPlant die?")
Understand the complete history of our plants
Derive insights that would be impossible with just a snapshot
Consistent care matters: daily watering and regular trimming lead to healthy growth; neglect leads to death

Further reading:

Martin Fowler's foundational article on Event Sourcing provides a comprehensive introduction to the pattern and its applications.
Shawn McCool's CQRS and Event Sourcing course - I bought this course back in 2018, but luckily it's now available for free on YouTube.