def generate_migration_body(tables)
      current_tables, new_tables = table_names(tables).partition do |table_name| 
        @db_table_names.include?(table_name)
      end

      add_line "change do"
      create_new_tables(new_tables, tables)
      alter_tables(current_tables, tables)
      add_line "end"
    end
def generate_migration_body(tables)
      current_tables, new_tables = table_names(tables).partition do |table_name| 
        @db_table_names.include?(table_name)
      end

      add_line "change do"
      create_new_tables(new_tables, tables)
      alter_tables(current_tables, tables)
      add_line "end"
    end
Generates the 'change' block of the migration.