ecto-migration-helper

Ecto Migration Helper

This skill helps create and manage Ecto migrations safely with proper patterns and rollback support.

When to Use

• Creating new migrations
• Modifying existing tables
• Adding/removing indexes
• Changing constraints
• Data migrations
• Rolling back migrations

Creating Migrations

Generate Empty Migration

mix ecto.gen.migration add_email_to_users

Creates: priv/repo/migrations/TIMESTAMP_add_email_to_users.exs

Migration Naming Conventions

• create_table_name - Creating new table
• add_field_to_table - Adding column
• remove_field_from_table - Removing column
• add_index_to_table_on_field - Adding index
• modify_field_in_table - Changing column type
• add_constraint_to_table - Adding constraint

Common Migration Patterns

Adding a Column

defmodule MyApp.Repo.Migrations.AddEmailToUsers do
  use Ecto.Migration

  def change do
    alter table(:users) do
      add :email, :string
    end
  end
end

Adding Column with Default

def change do
  alter table(:users) do
    add :active, :boolean, default: true, null: false
  end
end

Adding Column with Index

def change do
  alter table(:users) do
    add :email, :string
  end

  create unique_index(:users, [:email])
end

Adding Foreign Key

def change do
  alter table(:posts) do
    add :user_id, references(:users, on_delete: :delete_all), null: false
  end

  create index(:posts, [:user_id])
end

Removing a Column

def change do
  alter table(:users) do
    remove :old_field
  end
end

WARNING: Removing columns is irreversible with change. Use up/down:

def up do
  alter table(:users) do
    remove :old_field
  end
end

def down do
  alter table(:users) do
    add :old_field, :string
  end
end

Modifying Column Type

def change do
  alter table(:products) do
    modify :price, :decimal, precision: 10, scale: 2
  end
end

Renaming Column

def change do
  rename table(:users), :username, to: :name
end