Add Model

+++ title = "Add a model" description = "Generate a model with a migration, add fields to it, and run the migration to get working entities." date = 2021-05-01T18:10:00+00:00 updated = 2021-05-01T18:10:00+00:00 draft = false weight = 1 sort_by = "weight" template = "docs/page.html" aliases = ["/docs/the-app/models/"]

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

Goal: add a new database-backed model to a Loco app — a migration, a Sea-ORM entity, and your own model file to extend it — using the model generator.

This assumes a working Loco app with the with-db feature enabled (the default). For the full field-type mini-language and every generator kind, see Generators & field types. For the migration DSL used under the hood, see Schema & ColType DSL.

1. Generate the model

Run the model generator with a name and a list of field:type pairs:

$ cargo loco generate model posts title:string! content:text user:references

This does three things in one step:

1. Writes a migration under migration/src/ that creates a posts table.
2. Applies the migration against your development database.
3. Regenerates Sea-ORM entities into src/models/_entities/, and scaffolds src/models/posts.rs for your own model code.

You end up with:

src/
  models/
    _entities/
      posts.rs   <-- generated entity (Entity, Model, ActiveModel, Column, Relation)
    posts.rs     <-- your extension point
migration/
  src/
    m20240101_000002_posts.rs

Set the SKIP_MIGRATION environment variable if you want the generator to only write the migration file, without applying it or regenerating entities — useful when scripting several generate model calls back to back before running db migrate once at the end.

2. Read the field syntax

Each field:type pair follows a small suffix convention:

• no suffix → nullable column (Option<T>)
• ! → required column (NOT NULL)
• ^ → unique column (implies NOT NULL)

So title:string! is a required String, and content:text is a nullable Option<String>.

user:references is special: it doesn't name a column type, it declares a belongs-to foreign key. It adds a required user_id column referencing the users table (user:references? makes it nullable; user:references:author_id picks a custom column name). See Generators & field types § References for the full syntax.

3. Add more fields to an existing model

To add columns to a table you already created, generate a plain migration instead of a new model — name it Add<Columns>To<Table> so Loco infers an "add columns" migration:

$ cargo loco generate migration AddViewsToPosts views:int

Apply it and regenerate entities:

$ cargo loco db migrate
$ cargo loco db entities

Removing columns follows the mirror-image naming convention, Remove<Columns>From<Table>:

$ cargo loco generate migration RemoveViewsFromPosts views:int

4. Generate without timestamps (optional)

By default every table generated through the DSL gets created_at/updated_at columns. To opt out, pass --without-tz to model, migration, or scaffold:

$ cargo loco generate model posts title:string! content:text --without-tz

5. Verify

Confirm the migration applied and entities exist:

$ cargo loco db status
$ ls src/models/_entities/

Then write against the model directly — e.g. in a cargo loco playground script or a test:

use migration::Migrator;
use loco_rs::testing::prelude::*;
use myapp::models::_entities::posts;

let boot = boot_test::<App, Migrator>().await?;
let post = posts::ActiveModel {
    title: sea_orm::ActiveValue::set("hello".to_string()),
    user_id: sea_orm::ActiveValue::set(1),
    ..Default::default()
}
.insert(&boot.app_context.db)
.await?;

assert_eq!(post.title, "hello");

Result: a posts table exists in your database, posts::Entity/Model/ActiveModel compile, and src/models/posts.rs is where you add custom methods (e.g. Model::find_by_title) the same way examples/demo/src/models/users.rs extends the generated users entity.

Next

• Query data with the ConditionBuilder DSL.
• Foreign-key relationships and request/model validation beyond a single table.