Command

A command is a single function, which will be called (invoked) by someone with the expectation to get a result back.

Add a command to an existing service with purista add command.

Commands can access service resources (for example database clients/connections) via context.resources. Resources are provided when creating the service instance with serviceBuilder.getInstance(eventBridge, { resources: ... }).

Command lifecycle

1. optional input transform
2. payload/parameter validation
3. before guards
4. command function execution
5. output validation
6. after guards
7. optional output transform

What to read next

• The command builder
• Invoke another command
• Expose as HTTP endpoint
• Test a command

When to use

• You need request/response behavior.
• A caller expects success/error result semantics.
• You want strict validation on input/output contracts.

Common pitfalls

• mixing long-running asynchronous workflows into one command
• overusing broad payload schemas instead of explicit contracts
• forgetting to define output schema, then losing type guarantees

Checklist

• payload, parameter and output schemas are defined
• guards are used for auth/authz concerns
• command is exposed (or intentionally internal only)
• unit tests cover success and failure paths