删除 Rails 迁移中的重复列答案

【问题标题】：Remove duplicate columns in rails migration删除 Rails 迁移中的重复列
【发布时间】：2017-01-15 21:25:31
【问题描述】：

我的应用中有 Paperclip gem，然后我删除了它，我想再次添加它。但是，当我尝试rake db:migrate 时出现此错误：

 ActiveRecord::SchemaMigration Load (0.4ms)  SELECT "schema_migrations".* FROM "schema_migrations"
Migrating to AddAttachmentImageToPosts (20170115210207)
   (0.3ms)  BEGIN
== 20170115210207 AddAttachmentImageToPosts: migrating ========================
-- change_table(:posts)
   (0.9ms)  ALTER TABLE "posts" ADD "image_file_name" character varying
   (0.2ms)  ROLLBACK
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

PG::DuplicateColumn: ERROR:  column "image_file_name" of relation "posts" already exists
: ALTER TABLE "posts" ADD "image_file_name" character varying
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:155:in `async_exec'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:155:in `block in execute'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract_adapter.rb:472:in `block in log'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-4.2.5/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract_adapter.rb:466:in `log'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:154:in `execute'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_statements.rb:393:in `add_column'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/schema_statements.rb:423:in `add_column'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_definitions.rb:443:in `column'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:54:in `block (2 levels) in attachment'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:52:in `each_pair'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:52:in `block in attachment'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:51:in `each'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:51:in `attachment'
/home/ubuntu/workspace/db/migrate/20170115210207_add_attachment_image_to_posts.rb:4:in `block in up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_statements.rb:363:in `change_table'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:665:in `block in method_missing'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:634:in `block in say_with_time'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:634:in `say_with_time'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:654:in `method_missing'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:416:in `method_missing'
/home/ubuntu/workspace/db/migrate/20170115210207_add_attachment_image_to_posts.rb:3:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:571:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:611:in `exec_migration'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:592:in `block (2 levels) in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:591:in `block in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:590:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:768:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:998:in `block in execute_migration_in_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:1044:in `block in ddl_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `block in transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/transaction.rb:184:in `within_new_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/transactions.rb:220:in `transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:1044:in `ddl_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:997:in `execute_migration_in_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:959:in `block in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:955:in `each'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:955:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:823:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:801:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/tasks/database_tasks.rb:137:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/railties/databases.rake:44:in `block (2 levels) in <top (required)>'
/usr/local/rvm/gems/ruby-2.3.0/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'
/usr/local/rvm/gems/ruby-2.3.0/bin/ruby_executable_hooks:15:in `eval'
/usr/local/rvm/gems/ruby-2.3.0/bin/ruby_executable_hooks:15:in `<main>'
ActiveRecord::StatementInvalid: PG::DuplicateColumn: ERROR:  column "image_file_name" of relation "posts" already exists
: ALTER TABLE "posts" ADD "image_file_name" character varying
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:155:in `async_exec'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:155:in `block in execute'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract_adapter.rb:472:in `block in log'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-4.2.5/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract_adapter.rb:466:in `log'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:154:in `execute'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_statements.rb:393:in `add_column'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/schema_statements.rb:423:in `add_column'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_definitions.rb:443:in `column'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:54:in `block (2 levels) in attachment'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:52:in `each_pair'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:52:in `block in attachment'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:51:in `each'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:51:in `attachment'
/home/ubuntu/workspace/db/migrate/20170115210207_add_attachment_image_to_posts.rb:4:in `block in up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_statements.rb:363:in `change_table'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:665:in `block in method_missing'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:634:in `block in say_with_time'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:634:in `say_with_time'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:654:in `method_missing'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:416:in `method_missing'
/home/ubuntu/workspace/db/migrate/20170115210207_add_attachment_image_to_posts.rb:3:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:571:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:611:in `exec_migration'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:592:in `block (2 levels) in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:591:in `block in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:590:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:768:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:998:in `block in execute_migration_in_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:1044:in `block in ddl_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `block in transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/transaction.rb:184:in `within_new_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/transactions.rb:220:in `transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:1044:in `ddl_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:997:in `execute_migration_in_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:959:in `block in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:955:in `each'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:955:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:823:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:801:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/tasks/database_tasks.rb:137:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/railties/databases.rake:44:in `block (2 levels) in <top (required)>'
/usr/local/rvm/gems/ruby-2.3.0/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'
/usr/local/rvm/gems/ruby-2.3.0/bin/ruby_executable_hooks:15:in `eval'
/usr/local/rvm/gems/ruby-2.3.0/bin/ruby_executable_hooks:15:in `<main>'
PG::DuplicateColumn: ERROR:  column "image_file_name" of relation "posts" already exists
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:155:in `async_exec'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:155:in `block in execute'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract_adapter.rb:472:in `block in log'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-4.2.5/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract_adapter.rb:466:in `log'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:154:in `execute'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_statements.rb:393:in `add_column'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/postgresql/schema_statements.rb:423:in `add_column'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_definitions.rb:443:in `column'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:54:in `block (2 levels) in attachment'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:52:in `each_pair'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:52:in `block in attachment'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:51:in `each'
/usr/local/rvm/gems/ruby-2.3.0/gems/paperclip-5.1.0/lib/paperclip/schema.rb:51:in `attachment'
/home/ubuntu/workspace/db/migrate/20170115210207_add_attachment_image_to_posts.rb:4:in `block in up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/schema_statements.rb:363:in `change_table'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:665:in `block in method_missing'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:634:in `block in say_with_time'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:634:in `say_with_time'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:654:in `method_missing'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:416:in `method_missing'
/home/ubuntu/workspace/db/migrate/20170115210207_add_attachment_image_to_posts.rb:3:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:571:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:611:in `exec_migration'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:592:in `block (2 levels) in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:591:in `block in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/connection_pool.rb:292:in `with_connection'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:590:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:768:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:998:in `block in execute_migration_in_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:1044:in `block in ddl_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `block in transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/transaction.rb:184:in `within_new_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/connection_adapters/abstract/database_statements.rb:213:in `transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/transactions.rb:220:in `transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:1044:in `ddl_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:997:in `execute_migration_in_transaction'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:959:in `block in migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:955:in `each'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:955:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:823:in `up'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/migration.rb:801:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/tasks/database_tasks.rb:137:in `migrate'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-4.2.5/lib/active_record/railties/databases.rake:44:in `block (2 levels) in <top (required)>'
/usr/local/rvm/gems/ruby-2.3.0/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'
/usr/local/rvm/gems/ruby-2.3.0/bin/ruby_executable_hooks:15:in `eval'
/usr/local/rvm/gems/ruby-2.3.0/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

当我运行rails c 时，我得到了：

 2.3.0 :001 > Post.column_names
     => ["id", "title", "link", "description", "created_at", "updated_at", "user_id", "image_file_name", "image_content_type", "image_file_size", "image_updated_at", "cached_votes_total", "cached_votes_score", "cached_votes_up", "cached_votes_down", "cached_weighted_score", "cached_weighted_total", "cached_weighted_average", "image"]

我知道有一种方法可以删除“image_file_name”重复项，但我真的不知道如何对我的应用执行此操作。我确实找到了一些与我的问题相似的帖子，但没有真正解决它！

【问题讨论】：

如果您已经拥有该字段，为什么还要尝试再次添加？
因为我之前删除回形针的时候..我也删除了它的迁移
评论你的模型，你添加了附件，任何验证......然后运行迁移文件..
@Milind 我这样做了，但现在我收到此错误Post model missing required attr_accessor for 'image_file_name'
您在其他一些模型中具有必需的属性。在整个项目中搜索 image_file_name，我相信..您会得到它..然后将其注释掉并重新运行迁移，然后再次取消注释它。

标签： ruby-on-rails migration paperclip

【解决方案1】：

因为你删除了创建列的迁移，如果你创建一个迁移来删除它，在其他环境（生产）中会导致错误，因为一开始没有要删除的列。

假设您尚未将迁移部署到生产环境。您可以直接在数据库控制台中删除该列。

运行rails dbconsole

和

ALTER TABLE posts DROP COLUMN image_file_name;

【讨论】：

【解决方案2】：

首先，您永远不应该只删除迁移。如果你想删除一个字段，你应该为它创建一个新的迁移。

您现在有 2 个选项，或者您可以 rake db:migration:reset 重新创建您的整个数据库，或者您可以评论上次迁移的内容，运行 rake db:migrate 然后您可以取消评论。

【讨论】：

我做了第二个选项，它运行了 db:migrate。但是，当我尝试上传图片时，我得到了这个Post model missing required attr_accessor for 'image_file_name'
我现在应该试试rake db:migration:rest 吗？