an empty model (entity + migration + test)

+++ title = "Generate code with cargo loco generate" description = "Scaffold models, migrations, controllers, workers, and more with cargo loco generate <kind>, using the shared field:type mini-language." date = 2021-05-01T18:10:00+00:00 updated = 2021-05-01T18:10:00+00:00 draft = false weight = 60 sort_by = "weight" template = "docs/page.html"

[extra] lead = "" toc = true top = false +++

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
cargo loco generate controller posts index show

# 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

scaffold and controller are adaptive — there's no kind flag to pick. controller always generates a JSON API controller; scaffold generates a JSON API controller and, when the app has a frontend/, also emits typed React hooks and pages for the resource. The old --html/--htmx server-side views are gone (replaced by the React SPA frontend); --api is still accepted as a no-op for back-compat.

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.