Convert the table associated to a model into 'utf8_general_ci' (string columns + table)

convert_model_table_utf8.rb

class ConvertToUtf8

  DEFAULT_CONVERT_CHARACTER = 'utf8'
  DEFAULT_CONVERT_COLLATE   = 'utf8_general_ci'
  DEFAULT_CONVERT_COLUMNS   = {
    # ActiveRecord: SQL
    string: 'varchar(255)',
    text:   'text'
  }

  # Call example : ConvertToUtf8.new User
  def initialize model_class, **options
    options[:convert_columns]   ||= ConvertToUtf8::DEFAULT_CONVERT_COLUMNS
    options[:convert_character] ||= ConvertToUtf8::DEFAULT_CONVERT_CHARACTER
    options[:convert_collate]   ||= ConvertToUtf8::DEFAULT_CONVERT_COLLATE

    model_class   = model_class.constantize unless model_class.is_a? Class
    model_columns = model_class.columns

    options[:convert_columns].each do |rails_column, sql_column|
      fields_to_convert = model_columns.select{ |c| c.type == rails_column }.map(&:name)

      fields_to_convert.each do |field|
        ActiveRecord::Base.connection.execute("ALTER TABLE `#{model_class.table_name}` MODIFY `#{field}` #{sql_column} CHARACTER SET #{options[:convert_character]} COLLATE #{options[:convert_collate]};")
      end
    end

    ActiveRecord::Base.connection.execute("ALTER TABLE `#{model_class.table_name}` CONVERT TO CHARACTER SET #{options[:convert_character]} COLLATE #{options[:convert_collate]};")
  end

end