我对在轨道上开发相对较新。
我正在尝试使用以下命令迁移新创建的表：
$ rake db:migrate
但我经常收到与已存在的表有关的错误。但每当我尝试运行我的rails应用程序时，我都会收到迁移正在等待处理的错误。
我不介意删除该表，因为我刚刚开始处理这个应用程序，所以我删除了我之前的迁移，并且我运行了db：migrate命令，并且没有任何东西可以迁移。然后我将使用以下命令再次添加新模型：
$ rails generate model User name:string
然后给我一个预期的输出：
invoke active_record
create db/migrate/20141129134103_create_users.rb
identical app/models/user.rb
invoke test_unit
identical test/models/user_test.rb
identical test/fixtures/users.yml
但之后我跑了：
$ rake db:migrate --trace
我得到了这个输出：
** Invoke db:migrate (first_time)
** Invoke environment (first_time)
** Execute environment
** Invoke db:load_config (first_time)
** Execute db:load_config
** Execute db:migrate
== 20141129134103 CreateUsers: migrating ======================================
-- create_table(:users)
rake aborted!
StandardError: An error has occurred, all later migrations canceled:
Mysql2::Error: Table 'users' already exists: CREATE TABLE `users` (`id` int(11) auto_increment PRIMARY KEY, `name` varchar(255), `created_at` datetime, `updated_at` datetime) ENGINE=InnoDB/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `query'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/mysql2_adapter.rb:228:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:460:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in `block in method_missing'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `block in say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in `method_missing'
/home/barry/Documents/Programming/Rails Projects/homework/db/migrate/20141129134103_create_users.rb:3:in `change'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:595:in `exec_migration'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in `block in execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:1039:in `ddl_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in `execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in `up'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in `block (2 levels) in <top (required)>'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `call'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:172:in `invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:165:in `invoke'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:156:in `invoke_task'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block (2 levels) in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:121:in `run_with_threads'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:106:in `top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:84:in `block in run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:182:in `standard_exception_handling'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:79:in `run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/bin/rake:33:in `<top (required)>'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `load'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `<main>'
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'users' already exists: CREATE TABLE `users` (`id` int(11) auto_increment PRIMARY KEY, `name` varchar(255), `created_at` datetime, `updated_at` datetime) ENGINE=InnoDB
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `query'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/mysql2_adapter.rb:228:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:460:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in `block in method_missing'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `block in say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in `method_missing'
/home/barry/Documents/Programming/Rails Projects/homework/db/migrate/20141129134103_create_users.rb:3:in `change'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:595:in `exec_migration'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in `block in execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:1039:in `ddl_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in `execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in `up'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in `block (2 levels) in <top (required)>'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `call'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:172:in `invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:165:in `invoke'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:156:in `invoke_task'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block (2 levels) in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:121:in `run_with_threads'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:106:in `top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:84:in `block in run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:182:in `standard_exception_handling'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:79:in `run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/bin/rake:33:in `<top (required)>'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `load'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `<main>'
Mysql2::Error: Table 'users' already exists
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `query'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activesupport-4.1.8/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:303:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/mysql2_adapter.rb:228:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/schema_statements.rb:205:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:460:in `create_table'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:649:in `block in method_missing'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `block in say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:621:in `say_with_time'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:641:in `method_missing'
/home/barry/Documents/Programming/Rails Projects/homework/db/migrate/20141129134103_create_users.rb:3:in `change'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:595:in `exec_migration'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:579:in `block (2 levels) in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/benchmark.rb:279:in `measure'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:578:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in `with_connection'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:577:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:752:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:991:in `block in execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:1039:in `ddl_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:990:in `execute_migration_in_transaction'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:952:in `block in migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:948:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:807:in `up'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/migration.rb:785:in `migrate'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/railties/databases.rake:34:in `block (2 levels) in <top (required)>'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `call'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:240:in `block in execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:235:in `execute'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:179:in `block in invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/2.1.0/monitor.rb:211:in `mon_synchronize'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:172:in `invoke_with_call_chain'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/task.rb:165:in `invoke'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:156:in `invoke_task'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block (2 levels) in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `each'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:112:in `block in top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:121:in `run_with_threads'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:106:in `top_level'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:84:in `block in run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:182:in `standard_exception_handling'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/lib/rake/application.rb:79:in `run'
/home/barry/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/rake-10.4.0/bin/rake:33:in `<top (required)>'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `load'
/home/barry/.rbenv/versions/2.1.2/bin/rake:23:in `<main>'
Tasks: TOP => db:migrate
正如我所说，在运行我的rails应用程序之后，我得到了迁移正在等待处理的错误，我似乎无法理解什么是错的。如果您需要任何其他文件来帮助诊断此问题，请与我们联系。我正在做的与教程不同的一件事是我使用mysql而不是sqlite3。
提前谢谢你：）
答案 0 :(得分：5)
您正在rails中删除迁移。然而，实际的mysql表本身没有被触及（丢弃），然后你的大部分问题都源于两者不同步的事实。
在这种情况下，您的选择通常是：
- `rake db:migrate:down` # To have rails remove the table and keep in sync*
- delete ('drop table users') the table in mysql and then re-run the migrations.
- Use rake db:reset as indicated by jykim to drop the database.
展望未来，不要在不考虑现有的实际数据库表的情况下删除迁移。使用rails down migration和db reset来保持mysql数据库同步。在一天结束时，schema_migrations表需要正确。