### Install Dekiru::DataMigration Gem

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Instructions for installing the Dekiru::DataMigration gem using Bundler or gem install.

```ruby
gem 'dekiru-data_migration'
```

```bash
$ bundle install
```

```bash
$ gem install dekiru-data_migration
```

--------------------------------

### Dekiru Data Migration Runtime Options Example

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Shows how to execute a Dekiru::DataMigration::Operator with specific runtime options. This includes options for controlling side effect warnings, transaction usage, logging, and output destination.

```ruby
Dekiru::DataMigration::Operator.execute('Title', options) do
  # Processing content
end
```

--------------------------------

### Test Data Migration Class (RSpec - Ruby)

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Example of unit testing a data migration class using RSpec. It covers testing the `migration_targets` and `migrate_record` methods.

```ruby
# spec/migrations/demo_migration_spec.rb
RSpec.describe DemoMigration do
  let(:migration) { described_class.new }

  describe '#migration_targets' do
    it 'returns correct migration targets' do
      create_list(:user, 3, email: 'test@sonicgarden.jp', admin: false)
      create_list(:user, 2, email: 'other@example.com', admin: false)

      targets = migration.migration_targets
      expect(targets.count).to eq(3)
      expect(targets.all? { |u| u.email.include?('sonicgarden') }).to be true
    end
  end

  describe '#migrate_record' do
    it 'updates user to admin' do
      user = create(:user, admin: false)
      expect { migration.migrate_record(user) }
        .to change { user.reload.admin }.from(false).to(true)
    end
  end
end
```

--------------------------------

### Dekiru Data Migration Basic Configuration Options

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Lists and explains basic configuration options for Dekiru::DataMigration, including setting the maintenance script directory and custom transaction providers.

```ruby
# config/initializers/dekiru.rb
Dekiru::DataMigration.configure do |config|
  # Output directory for maintenance scripts (default: "scripts")
  config.maintenance_script_directory = 'scripts/maintenance'

  # Custom transaction provider (default: Dekiru::DataMigration::TransactionProvider.new)
  config.transaction_provider = MyTransactionProvider.new
end
```

--------------------------------

### Legacy Block-based Data Migration (Ruby)

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Demonstrates the legacy block-based approach for data migration using `Dekiru::DataMigration::Operator.execute`.

```ruby
# scripts/legacy_demo.rb
Dekiru::DataMigration::Operator.execute('demo_migration') do
  # write here
end
```

--------------------------------

### Execute Data Migration with Operator Script (Ruby)

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Demonstrates how to use Dekiru::DataMigration::Operator.execute to perform data migrations using a block-based approach. This method includes progress display and logging.

```ruby
# scripts/demo.rb
Dekiru::DataMigration::Operator.execute('Grant admin privileges to users') do
  targets = User.where("email LIKE '%sonicgarden%'")

  log "Target user count: #{targets.count}"
  find_each_with_progress(targets) do |user|
    user.update!(admin: true)
  end

  log "Updated user count: #{User.where("email LIKE '%sonicgarden%'").where(admin: true).count}"
end
```

--------------------------------

### Define Data Migration with Class (Ruby)

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Shows how to define data migration logic as a class, inheriting from Dekiru::DataMigration::Migration. This approach is recommended for easier testing and better organization.

```ruby
# scripts/20230118_demo_migration.rb
class DemoMigration < Dekiru::DataMigration::Migration
  def migration_targets
    User.where("email LIKE '%sonicgarden%'").where(admin: false)
  end

  def migrate_record(user)
    user.update!(admin: true)
  end

  def migrate
    super
    log "Updated user count: #{User.where(admin: true).count}"
  end
end

DemoMigration.run
```

--------------------------------

### Configure Output Directory for Dekiru Data Migration

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Sets the output directory for maintenance scripts in Dekiru Data Migration. This configuration is applied within the application's initializers.

```ruby
# config/initializers/dekiru.rb
Dekiru::DataMigration.configure do |config|
  config.maintenance_script_directory = 'scripts/maintenance'
end
```

--------------------------------

### Custom Transaction Management for Multi-Database Applications

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Demonstrates how to implement custom transaction handling for Dekiru::DataMigration::Operator when dealing with multiple databases. It involves defining a custom TransactionProvider that utilizes application-specific transaction methods.

```ruby
# app/models/legacy_record.rb
class LegacyRecord < ApplicationRecord
  connects_to database: { writing: :legacy, reading: :legacy }
end

# app/models/application_record.rb
class ApplicationRecord < ActiveRecord::Base
  connects_to database: { writing: :primary, reading: :primary }

  def self.with_legacy_transaction
    ActiveRecord::Base.transaction do
      LegacyRecord.transaction do
        yield
      end
    end
  end
end
```

```ruby
# config/initializers/dekiru.rb
class MyTransactionProvider < Dekiru::DataMigration::TransactionProvider
  def within_transaction(&)
    ApplicationRecord.with_legacy_transaction(&)
  end
end

Dekiru::DataMigration.configure do |config|
  config.transaction_provider = MyTransactionProvider.new
end
```

--------------------------------

### Generated Maintenance Script Template (Ruby)

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

A template for a generated maintenance script file, outlining the structure for defining migration targets and record migration logic.

```ruby
# scripts/20230118_demo_migration.rb
# frozen_string_literal: true

class DemoMigration < Dekiru::DataMigration::Migration
  def migration_targets
    # 移行対象を返すActiveRecord::Relationを定義
    # 例: User.where(some_condition: true)
    raise NotImplementedError, 'migration_targets method must be implemented'
  end

  def migrate_record(record)
    # 個別レコードの更新処理を定義
    # 例: record.update!(some_attribute: new_value)
    raise NotImplementedError, 'migrate_record method must be implemented'
  end
end

DemoMigration.run
```

--------------------------------

### Monitor Side Effects During Data Migration (Ruby)

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Enables monitoring of side effects such as database writes, job enqueuing, and email sending during data migration by passing `warning_side_effects: true` to the `execute` method.

```ruby
Dekiru::DataMigration::Operator.execute('Grant admin privileges to users', warning_side_effects: true) do
  # Processing content...
end
```

--------------------------------

### Generate Maintenance Script (Bash)

Source: https://github.com/sonicgarden/dekiru-data_migration/blob/main/README.md

Command to generate a new maintenance script file using the Rails generator. The filename will be prefixed with the current date.

```bash
$ bin/rails g maintenance_script demo_migration
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.