ecto-guidelines

name	ecto-guidelines
description	Ecto best practices covering preloading, schema types, changeset validation, field access, security, and migration conventions. Use when working with Ecto schemas, changesets, queries, or migrations.

Ecto Guidelines

Preloading Associations

• Always preload Ecto associations in queries when they'll be accessed in templates:

# If the template needs message.user.email
messages = Repo.all(from m in Message, preload: [:user])

Seeds and Queries

• Remember import Ecto.Query and other supporting modules when you write seeds.exs

Schema Field Types

• Ecto.Schema fields always use the :string type, even for :text columns:

field :name, :string
field :description, :string  # Even if the DB column is :text

Changeset Validation

• Ecto.Changeset.validate_number/2 DOES NOT SUPPORT the :allow_nil option. By default, Ecto validations only run if a change for the given field exists and the change value is not nil, so such an option is never needed

Accessing Changeset Fields

• You must use Ecto.Changeset.get_field(changeset, :field) to access changeset fields
• Never use map access syntax (changeset[:field]) on changesets

Security: Programmatic Fields

• Fields which are set programmatically, such as user_id, must not be listed in cast calls or similar for security purposes. Instead they must be explicitly set when creating the struct:

# GOOD: Set user_id explicitly, not through cast
%Message{}
|> Message.changeset(params)  # cast only includes :content, :subject, etc.
|> Ecto.Changeset.put_assoc(:user, user)

Migrations

• Always invoke mix ecto.gen.migration migration_name_using_underscores when generating migration files, so the correct timestamp and conventions are applied