Ecto.Migration provides a database-independent DSL for writing and running migrations in Phoenix and Elixir applications.
CLI Migration Commands
# Generate migration file
mix ecto.gen.migration add_status_to_orders
# Run pending migrations
mix ecto.migrate
# Roll back the most recent migration step
mix ecto.rollback
# Check migration status
mix ecto.migrations
Table Definition DSL
defmodule MyApp.Repo.Migrations.CreateDocuments do
use Ecto.Migration
def change do
create table(:documents) do
add :title, :string, size: 100, null: false
add :body, :text
add :price, :decimal, precision: 10, scale: 2
add :views, :integer, default: 0
add :active, :boolean, default: true, null: false
add :metadata, :map # JSON / JSONB
add :published_at, :utc_datetime
# Foreign key reference
add :author_id, references(:users, on_delete: :delete_all), null: false
timestamps() # Adds inserted_at and updated_at
end
end
end
Modifying Existing Tables (alter)
alter table(:documents) do
add :subtitle, :string
modify :title, :string, size: 255
remove :views
end
Indices & Constraints
# Unique index
create unique_index(:users, [:email])
# Composite index with concurrent creation (PostgreSQL)
create index(:orders, [:user_id, :status], concurrently: true)
# Drop index
drop index(:orders, [:status])
Raw SQL Execution
# Execute arbitrary SQL commands in migration
execute "CREATE EXTENSION IF NOT EXISTS citext;"