AgentSkillsCN

ecto-guidelines

涵盖预加载、Schema 类型、Changeset 验证、字段访问、安全性，以及迁移规范等 Ecto 最佳实践。当您需要处理 Ecto Schema、Changesets、查询，或进行迁移操作时，可选用此方法。

SKILL.md
--- frontmatter
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:
elixir
# 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:
elixir
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:
elixir
# 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