我有两个迁移.. self.down方法在一个上失败并在另一个上工作，即使它们看起来与我相同（不同的表，相同的列和类型。）如果我用“varchar”替换：string ）“它有效，但我不明白为什么：在这种情况下字符串会失败。
有人可以看到我可能做错了吗？
我在OSX上使用Rails / ActiveRecord 2.1.0和Mysql 5.6.13
这个失败了。
def self.down
remove_column :comments, :employee_id
add_column :comments, :employee_id, :string #"varchar(255)" will work
Comment.all.each do |c|
c.employee_id = c.empno
c.send(:update_without_callbacks)
end
remove_column :comments, :empno
end
这个有效
def self.down
remove_column :supervisor_options, :employee_id
add_column :supervisor_options, :employee_id, :string
SupervisorOption.all.each do |c|
c.employee_id = c.empno
c.send(:update_without_callbacks)
end
remove_column :supervisor_options, :empno
end
我在db：migrate期间获得的堆栈是......
rake aborted!
Mysql2::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(255)' at line 1: ALTER TABLE `comments` ADD `employee_id` varchar(255)(255)
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/connection_adapters/abstract_adapter.rb:147:in `log'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-mysql2-adapter-0.0.3/lib/active_record/connection_adapters/mysql2_adapter.rb:265:in `execute'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-mysql2-adapter-0.0.3/lib/active_record/connection_adapters/mysql2_adapter.rb:450:in `add_column'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:330:in `send'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:330:in `method_missing'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:310:in `say_with_time'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:310:in `say_with_time'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:326:in `method_missing'
./db/migrate//20140501155627_rename_employee_id.rb:17:in `down_without_benchmarks'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:264:in `send'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:264:in `migrate'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:264:in `migrate'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:430:in `migrate'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:420:in `each'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:420:in `migrate'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:361:in `down'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/activerecord-2.1.0/lib/active_record/migration.rb:341:in `migrate'
/Users/gakins/.rvm/gems/ree-1.8.7-2012.02@gaimplan/gems/rails-2.1.0/lib/tasks/databases.rake:99