Issuing commands

Commands are how you ask EvidentSource to do something. Every command is routed to a State Change component, whose decide function validates it and returns the events to append.

Command shape

Every command has:

• type — the command name (e.g. CreateTodo)
• subject — the entity the command is about
• data — the command-specific payload
• metadata (optional) — correlation IDs, effective time, caller context

The schema for a command is defined by whatever State Change component handles it.

REST

curl -X POST https://sandbox.evidentsource.com/v1/commands \
  -H "Content-Type: application/json" \
  -d '{
    "database": "todomvc",
    "command": {
      "type": "CreateTodo",
      "subject": "todo-123",
      "data": { "title": "Try the Sandbox" }
    }
  }'

The response includes the revision number assigned to the resulting event(s).

gRPC

Use the AppendCommand RPC on the EventStore service. See gRPC API.

From an SDK

Every SDK exposes a typed sendCommand / send_command method. See Connecting with an SDK.

Concurrency and errors

Commands carry DCB conditions at the decide layer. If a condition fails at append time, the call returns a conflict error — the SDK lets you retry with fresh state. If decide itself rejects the command, you get a structured error with the rejection reason.

Next

• Reading state views — read back what your commands produced.