ecto-guidelines

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