Ecto Migration

Overview

The ecto-migration skill generates new Ecto migration files for the Blockscout project using the Mix task. Migrations are used to evolve the database schema over time in a versioned and controlled manner.

When to Use

• When creating new database tables
• When modifying existing table structures (add/remove/change columns)
• When adding or removing database indexes
• When performing data migrations or transformations
• When implementing database constraints or relationships

How to Apply

Run the following command from the workspace root:

mix ecto.gen.migration [migration_name] -r Explorer.Repo

Replace [migration_name] with a descriptive name for your migration using snake_case (e.g., add_users_table, alter_transactions_status).

What It Does

• Creates a new migration file in apps/explorer/priv/repo/migrations/ directory
• Generates a timestamped filename to ensure proper ordering
• Provides a basic migration template with change/0 or up/0 and down/0 functions
• Targets the Explorer.Repo repository specifically

Example Usage

Generate a migration to add a new column:

mix ecto.gen.migration add_metadata_to_blocks -r Explorer.Repo

This creates a file like:

• apps/explorer/priv/repo/migrations/20260220123456_add_metadata_to_blocks.exs

Then edit the generated file to implement your schema changes:

defmodule Explorer.Repo.Migrations.AddMetadataToBlocks do
  use Ecto.Migration

  def change do
    alter table(:blocks) do
      add :metadata, :jsonb
    end
  end
end

Notes

• Always use descriptive migration names
• The -r Explorer.Repo flag specifies the repository (required for umbrella apps)
• Migration files are timestamped automatically to maintain order
• After creating a migration, edit it to implement the actual schema changes
• Run mix ecto.migrate to apply the migration to your database
• Use mix ecto.rollback to revert the last migration if needed
• For complex operations, consider using up/0 and down/0 instead of change/0