CQRS and Event Sourcing Practice Project

This project creates a JSON API around patient records. The write API implements event sourcing based on these immutable patient events - admit patient, transfer patient, discharge patient, update patient name and update patient age. These events are aggregated asynchronously to generate a most recent patient record in the database. The read API just queries the database for these generated record(s).

Directory Structure

Directory	Description
activities	Contains temporal activities
cmd	Contains program entrypoint in server subpackage
config	Configuration settings for db, temporal and api server
db	Database client
ent	Ent ORM schema and generated files
eventstore	Event store implementation using PostgreSQL
handlers	Container HTTP handlers (subpackages seggregate commands and queries handlers)
repositories	Contains repositories and models
server	API server setup
workflows	Contains temporal workflows

Application Configuration (Environment Variables)

Variable	Description
PSQL_HOST	Host name for PostgreSQL database
PSQL_PORT	Port for PostgreSQL database
PSQL_USER	PostgreSQL database user name
PSQL_PASSWORD	PostgreSQL database user password
PSQL_DB	PostgreSQL database name
GIN_MODE	debug or release mode for Gin
ENV	Application mode: dev or prod
SERVER_PORT	Server port to listen on (default: 3001)
TEMPORAL_HOST	Temporal host name
TEMPORAL_PORT	Temporal port number
TEMPORAL_NAMESPACE	Temporal namespace to use

Build/Run (Docker Compose)

Run the following steps to build/run the application -

1. cp .env.example .env
2. docker compose up --build -d

Now, docker containers for postgresql server, temporal server and the application server should be up and running and you can play with the API endpoints.

You can also access temporal web ui at this address: http://localhost:8080 and see which workflows are being executed.

Build/Run (Manual)

1. Run cp .env.example .env command and set the environment variables for postgresql and temporal in the .env file.
2. Build command - go build -o api ./cmd/server
3. Run command - ./api

Now, application server should be up and running and you can play with the API endpoints.

Note: This manual build/run requires pre-running instances of Temporal and PostgreSQL. The application server will connect with these instances.

Endpoints

Base URL: http://localhost:3001

The API exposes the following endpoints -

Commands

Admit New Patient

POST /patient/admit

Request Body

{
    "name": "Foo Name",
    "ward": 10,
    "age": 25
}

The response contains id field which is the ID for new patient.

Transfer Patient to Ward

POST /patient/transfer

Request Body

{
    "id": "<patient-id-here>",
    "ward": 11
}

Discharge Patient

POST /patient/discharge

Request Body

{
    "id": "<patient-id-here>",
}

Update Patient Name

POST /patient/updateName

Request Body

{
    "id": "<patient-id-here>",
    "name": "New Foo Name",
}

Update Patient Age

POST /patient/updateAge

Request Body

{
    "id": "<patient-id-here>",
    "age": 30,
}

Queries

Get All Patients

GET /patient/all

Get Patient By ID

GET /patient/id/<patient-id-here>

Get Patient By Name

GET /patient/name/<patient-name>