Concepts

This section covers the core concepts of Operandi: Arguments, Steps, Outputs, Context, Errors, and Callbacks.

Service Execution Flow

When you call MyService.run(args), the following happens:

┌──────────────────────────────────────────────────────────────┐
│                      Service.run(args)                       │
├──────────────────────────────────────────────────────────────┤
│  1. Load default values for arguments and outputs            │
│  2. Validate argument types                                  │
│  3. Run before_service_run callbacks                         │
├──────────────────────────────────────────────────────────────┤
│  4. Begin around_service_run callback                        │
│  5. Begin database transaction (if use_transactions: true)   │
│     ┌─────────────────────────────────────────────────────┐  │
│     │  6. Execute steps in order                          │  │
│     │     - Run before_step_run / around_step_run         │  │
│     │     - Execute step method                           │  │
│     │     - Run after_step_run / on_step_success          │  │
│     │     - Skip if condition (if:/unless:) not met       │  │
│     │     - Stop if errors.break? is true                 │  │
│     │     - Stop if stop! was called                      │  │
│     ├─────────────────────────────────────────────────────┤  │
│     │  7. On error → Rollback transaction                 │  │
│     │     On success → Commit transaction                 │  │
│     └─────────────────────────────────────────────────────┘  │
│  8. End around_service_run callback                          │
├──────────────────────────────────────────────────────────────┤
│  9. Run steps marked with always: true (unless stop! called) │
│ 10. Validate output types (if success)                       │
│ 11. Copy errors/warnings to parent service (if in context)   │
│ 12. Run after_service_run callback                           │
│ 13. Run on_service_success or on_service_failure callback    │
├──────────────────────────────────────────────────────────────┤
│ 14. Return service instance                                  │
│     - service.success? / service.failed?                     │
│     - service.outputs / service.errors                       │
└──────────────────────────────────────────────────────────────┘

Arguments

Arguments are the inputs provided to a service when it is invoked. They can be validated by type, assigned default values, and be designated as optional or required.

Steps

Steps are the fundamental units of work within a service, representing each individual task a service performs. They can be executed conditionally or skipped.

Outputs

Outputs are the results produced by a service upon its completion. They can have default values and be validated by type.

Context

Context refers to the shared state that passes between services in a service chain, enabling the transfer of arguments and error states from one service to another.

Errors

Errors occur during service execution and cause execution to halt. When an error occurs, all services in the same context chain stop, and database transactions are rolled back (configurable).

Callbacks

Callbacks allow you to run custom code at specific points during service and step execution. They're perfect for logging, benchmarking, auditing, and other cross-cutting concerns.

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