ruby

Rails 5에서 API는 테이블 / 뷰 , 집합 적으로 데이터 소스 와 관련 하여 명백해졌습니다 .

# Tables and views
ActiveRecord::Base.connection.data_sources
ActiveRecord::Base.connection.data_source_exists? 'kittens'

# Tables
ActiveRecord::Base.connection.tables
ActiveRecord::Base.connection.table_exists? 'kittens'

# Views
ActiveRecord::Base.connection.views
ActiveRecord::Base.connection.view_exists? 'kittens'

Rails 2, 3 & 4에서 API는 테이블 에 관한 것 입니다.

# Listing of all tables and views
ActiveRecord::Base.connection.tables

# Checks for existence of kittens table/view (Kitten model)
ActiveRecord::Base.connection.table_exists? 'kittens'

마이그레이션 상태 얻기 :

# Tells you all migrations run
ActiveRecord::Migrator.get_all_versions

# Tells you the current schema version
ActiveRecord::Migrator.current_version

마이그레이션 또는 메타 데이터에 더 많은 API가 필요한 경우 다음을 참조하십시오.

• ActiveRecord :: SchemaMigration
  이것은 테이블 의 ActiveRecord::Base클래스입니다schema_migrations
• 
  마이그레이션이 실행될 때 모든 작업이 수행되는 ActiveRecord :: Migrator

답변

drop_table :kittens if (table_exists? :kittens)
ActiveRecord::Migration.drop_table :kittens if (ActiveRecord::Base.connection.table_exists? :kittens)

drop_table :kittens, if_exists: true

if ActiveRecord::Base.connection.data_source_exists? 'table_name'
   drop_table :table_name
end

drop_table :table_name, if_exists: true

class Dog < ApplicationRecord
  # something
end

do_something if Dog.table_exists?