我想这是我应该用GitHub支持我的工作的另一个原因，但是唉，我还没有。
我想要回滚的迁移是这样的：
class AddAssociationToTables < ActiveRecord::Migration
def change
add_column :articles, :user, :belongs_to
end
end
它显然没有很好地形成，因为它似乎已从数据库中完全删除了我的article表。
我试过rake db:rollback:status并且没有任何“遗漏”或任何东西。
我要跳过复制粘贴整个痕迹。
我试图阻止迁移并运行它。这就是我写的：
class RemoveAssociationFromArticle < ActiveRecord::Migration
def change
remove_column :articles, :user, :belongs_to
end
end
但是当我试图用rake db:migrate运行时，我得到了同样的错误。
编辑好了这里首先是回滚的整个跟踪，然后是迁移尝试
== AddAssociationToTables: reverting =========================================
-- remove_column(:articles, :user, :belongs_to)
rake aborted!
An error has occurred, this and all later migrations canceled:
undefined method `to_sym' for nil:NilClass/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:215:in `column'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:545:in `block (2 levels) in copy_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:538:in `each'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:538:in `block in copy_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:184:in `create_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:535:in `copy_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:528:in `move_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:521:in `block in alter_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/database_statements.rb:200:in `transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:520:in `alter_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:463:in `remove_column'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:625:in `block in method_missing'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:597:in `block in say_with_time'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:597:in `say_with_time'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:617:in `method_missing'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:462:in `block in revert'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:461:in `each'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:461:in `revert'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:569:in `exec_migration'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:555:in `block (2 levels) in migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:554:in `block in migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:553:in `migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:709:in `migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:959:in `block in execute_migration_in_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:1005:in `block in ddl_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/database_statements.rb:202:in `block in transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/database_statements.rb:210:in `within_new_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/database_statements.rb:202:in `transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/transactions.rb:209:in `transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:1005:in `ddl_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:958:in `execute_migration_in_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:920:in `block in migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:916:in `each'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:916:in `migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:771:in `down'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:857:in `move'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:753:in `rollback'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/railties/databases.rake:126:in `block (2 levels) in <top (required)>'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/bin/ruby_executable_hooks:15:in `eval'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => db:rollback
(See full trace by running task with --trace)
== RemoveAssociationFromArticle: migrating ===================================
-- remove_column(:articles, :user, :belongs_to)
rake aborted!
An error has occurred, this and all later migrations canceled:
undefined method `to_sym' for nil:NilClass/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:215:in `column'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:545:in `block (2 levels) in copy_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:538:in `each'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:538:in `block in copy_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:184:in `create_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:535:in `copy_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:528:in `move_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:521:in `block in alter_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/database_statements.rb:200:in `transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:520:in `alter_table'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/sqlite3_adapter.rb:463:in `remove_column'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:625:in `block in method_missing'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:597:in `block in say_with_time'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:597:in `say_with_time'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:617:in `method_missing'
/home/macs/code/my_apps/rails_apps/satisfactory/dec1/whatis/db/migrate/20131202144933_remove_association_from_article.rb:3:in `change'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:571:in `exec_migration'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:555:in `block (2 levels) in migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:554:in `block in migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:553:in `migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:709:in `migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:959:in `block in execute_migration_in_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:1005:in `block in ddl_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/database_statements.rb:202:in `block in transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/database_statements.rb:210:in `within_new_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/connection_adapters/abstract/database_statements.rb:202:in `transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/transactions.rb:209:in `transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:1005:in `ddl_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:958:in `execute_migration_in_transaction'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:920:in `block in migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:916:in `each'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:916:in `migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:764:in `up'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/migration.rb:742:in `migrate'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/gems/activerecord-4.0.1/lib/active_record/railties/databases.rake:42:in `block (2 levels) in <top (required)>'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/bin/ruby_executable_hooks:15:in `eval'
/home/macs/.rvm/gems/ruby-2.0.0-p247@railstutorial_rails_4_0/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
答案 0 :(得分：1)
第三个参数应该是列的类型。
正确的语法是：
add_column :articles, :user_id, :integer
:belongs_to参数可能会导致与ActiveRecord方法发生冲突！
答案 1 :(得分：1)
如果它首先没有正确迁移，请不要担心回滚。只需修复迁移并尝试再次迁移即可。
您的迁移应该是：
add_column :articles, :user, :references
belongs_to适用于模型类，而不适用于迁移。如果它无法执行任何操作，您可以随时重新创建数据库以重新启动（并丢失所有数据）。
$ rake db:drop db:create db:migrate
开始使用版本控制，并在生命的某个时刻慢慢仔细地阅读所有这些http://guides.rubyonrails.org/migrations.html