Generate code with cargo loco generate

Goal: scaffold application code (models, migrations, controllers, workers, mailers, deployment files, …) from Loco’s built-in templates instead of hand-writing boilerplate.

1. Know the constraint: debug builds only

cargo loco generate (alias g) is compiled only in debug builds — #[cfg(debug_assertions)] gates the whole subcommand (src/cli.rs). It’s available whenever you run your app the normal dev way (cargo run, cargo loco start, cargo test), but it is not present in a --release binary. model/migration/scaffold are additionally gated on the with-db feature (on by default).

2. Run a generator

# an empty model (entity + migration + test)
cargo loco generate model posts

# a model with typed fields
cargo loco generate model posts title:string! content:text

# a full CRUD resource: entity + migration + controller + routes + tests
cargo loco generate scaffold posts title:string! user:references

# controller only, no model/migration (an `index` action is always generated,
# so name only the extra actions you want)
cargo loco generate controller posts show publish

# non-DB generators
cargo loco generate task cleanup_old_sessions
cargo loco generate worker send_digest
cargo loco generate mailer welcome
cargo loco generate scheduler
cargo loco generate data countries
cargo loco generate deployment docker

Every generator writes files relative to your project root and prints what it created (or, for model/migration/scaffold, injects a mod line into the relevant mod.rs).

3. Pick the right kind

Kind	Needs with-db	What you get
model	yes	Sea-ORM entity + model file + migration + a starter test in tests/models/
migration	yes	Standalone migration file (add/remove columns, join tables, or an empty stub — inferred from the name)
scaffold	yes	Full CRUD: entity, migration, DTOs, controller, routes, a model test — plus typed React hooks/pages when the app has a frontend/
controller	no	Controller + routes + tests, no model
task	no	One-off/CLI task stub, registered automatically
scheduler	no	config/scheduler.yaml starter
worker	no	Background worker stub, registered automatically
mailer	no	Mailer struct + embedded subject/html/text templates
data	no	Data-loader struct + a static data/<name>/data.json
deployment	no	docker, nginx, or lambda deployment files
override	no	Copies a built-in template locally so you can edit it — see Override built-in templates

scaffold and controller are adaptive — no kind flag. They generate a JSON API by default, and a scaffold additionally emits typed React hooks/pages when the app has a frontend/. (The old --api/--html/--htmx flags were removed in 1.0: --api is still accepted as a no-op so existing commands keep working; server-rendered HTML/HTMX views were replaced by the React SPA frontend.)

Scaffolded routes require a JWT by default, so curl-ing one without a bearer token answers 401 — pass --no-auth for a public resource. A generated controller is public by default; --auth is its opt-in mirror. See Authentication on generated routes.

This is a summary for orientation only — the exhaustive, verified dictionary of every kind, every flag, and migration-name inference rules is the Generators & field types reference; the raw CLI flag shapes are also in the CLI reference.

4. Use the field-type mini-language

model, migration, and scaffold all take name:type pairs after the resource name. The full table of ~50 base types (with their !/^ suffix variants, arities, and Rust types) lives in the field-type mini-language reference — check it before guessing a type name. A few load-bearing facts to keep in mind while typing field lists:

• No suffix = nullable (Option<T>); ! = required; ^ = unique (implies required). Not every type has a ^ form (bool, tstz, json don’t).
• int is i64/BIGINT in Loco 1.0 (it was i32 before) — big_int is just an alias. Use small_int/small_unsigned if you need a 16-bit column.
• name:references adds a required belongs-to foreign key (name_id); name:references? makes it nullable; name:references:custom_id (optionally with ?) picks the FK column name explicitly.
• array types take the element type as a second colon segment: tags:array:string, scores:array!:int.

cargo loco generate model movies long_title:string director:references award:references:prize_id

5. Apply generated migrations

Generating a migration (standalone or via scaffold/model) only writes the file — it doesn’t touch the database. Apply it and regenerate entities:

cargo loco db migrate && cargo loco db entities

Verify it

cargo build          # generators need a debug build to even be available
cargo loco generate model posts title:string!
cargo loco db migrate
cargo test

A successful generator run prints the list of files it created/modified; cargo build (or cargo check) then confirms the generated code compiles, and cargo test runs the starter test the generator scaffolded for you.