Ecto Schemas

Master Ecto schema definitions to model your database entities effectively in Elixir applications.

Basic Schema Definition

defmodule MyApp.Accounts.User do use Ecto.Schema import Ecto.Changeset

schema "users" do field :email, :string field :name, :string field :age, :integer field :is_active, :boolean, default: true field :role, Ecto.Enum, values: [:user, :admin, :moderator]

timestamps()

end

def changeset(user, attrs) do user |> cast(attrs, [:email, :name, :age, :is_active, :role]) |> validate_required([:email, :name]) |> validate_format(:email, ~r/@/) |> validate_number(:age, greater_than: 0) |> unique_constraint(:email) end end

Field Types

schema "products" do

Basic types

field :name, :string field :price, :decimal field :quantity, :integer field :is_available, :boolean field :rating, :float

Date and time

field :released_on, :date field :sale_starts_at, :naive_datetime field :sale_ends_at, :utc_datetime

Complex types

field :tags, {:array, :string} field :metadata, :map field :settings, {:map, :string} # map with string values

Binary data

field :image_data, :binary field :uuid, :binary_id

timestamps() end

Associations

defmodule MyApp.Blog.Post do use Ecto.Schema

schema "posts" do field :title, :string field :body, :string

# Belongs to
belongs_to :author, MyApp.Accounts.User

# Has many
has_many :comments, MyApp.Blog.Comment

# Has one
has_one :featured_image, MyApp.Blog.Image

# Many to many
many_to_many :tags, MyApp.Blog.Tag, join_through: "posts_tags"

timestamps()

end end

defmodule MyApp.Blog.Comment do use Ecto.Schema

schema "comments" do field :content, :string

belongs_to :post, MyApp.Blog.Post
belongs_to :user, MyApp.Accounts.User

timestamps()

end end

Embedded Schemas

defmodule MyApp.Accounts.Address do use Ecto.Schema

Embedded schema - stored as JSON in parent

embedded_schema do field :street, :string field :city, :string field :state, :string field :zip, :string field :country, :string, default: "US" end

def changeset(address, attrs) do address |> cast(attrs, [:street, :city, :state, :zip, :country]) |> validate_required([:street, :city, :state, :zip]) end end

defmodule MyApp.Accounts.User do use Ecto.Schema

schema "users" do field :name, :string

# Single embedded
embeds_one :billing_address, MyApp.Accounts.Address, on_replace: :update

# Multiple embedded
embeds_many :shipping_addresses, MyApp.Accounts.Address, on_replace: :delete

timestamps()

end

def changeset(user, attrs) do user |> cast(attrs, [:name]) |> cast_embed(:billing_address) |> cast_embed(:shipping_addresses) end end

Virtual Fields

defmodule MyApp.Accounts.User do use Ecto.Schema

schema "users" do field :email, :string field :password_hash, :string

# Virtual fields - not persisted
field :password, :string, virtual: true
field :password_confirmation, :string, virtual: true
field :full_name, :string, virtual: true

timestamps()

end

def changeset(user, attrs) do user |> cast(attrs, [:email, :password, :password_confirmation]) |> validate_required([:email, :password]) |> validate_confirmation(:password) |> hash_password() end

defp hash_password(changeset) do case get_change(changeset, :password) do nil -> changeset password -> put_change(changeset, :password_hash, Bcrypt.hash_pwd_salt(password)) end end end

When to Use This Skill

Use ecto-schemas when you need to:

• Define database table structures

• Model relationships between entities

• Create embedded documents

• Handle complex data types

• Implement virtual computed fields

Best Practices

• Use meaningful schema module names

• Keep schemas focused on data structure

• Use embedded schemas for nested JSON

• Define changesets in the schema module

• Use Ecto.Enum for constrained values

• Add database constraints with unique_constraint

Common Pitfalls

• Forgetting timestamps() in schemas

• Not handling on_replace for embeds

• Mixing business logic into schemas

• Forgetting to add associations on both sides

• Not using virtual fields for sensitive data

• Overusing embedded schemas when separate tables are better