对我来说,创建模型,运行迁移,销毁它,再次创建相同的模型报告sql异常似乎很奇怪：
project|master ⇒ rails g model name name
invoke active_record
create db/migrate/20130417185814_create_names.rb
create app/models/name.rb
project|master⚡ ⇒ rake db:migrate
== CreateNames: migrating ====================================================
-- create_table(:names)
-> 0.0020s
== CreateNames: migrated (0.0021s) ===========================================
project|master⚡ ⇒ rails d model name
invoke active_record
remove db/migrate/20130417185814_create_names.rb
remove app/models/name.rb
project|master⚡ ⇒ rake db:migrate
project|master⚡ ⇒ rails g model name test
invoke active_record
create db/migrate/20130417185845_create_names.rb
create app/models/name.rb
project|master⚡ ⇒ rake db:migrate
== CreateNames: migrating ====================================================
-- create_table(:names)
rake aborted!
An error has occurred,this and all later migrations canceled:
sqlite3::sqlException: table "names" already exists: CREATE TABLE "names" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,"test" varchar(255),"created_at" datetime NOT NULL,"updated_at" datetime NOT NULL) /path/project/db/migrate/20130417185845_create_names.rb:3:in `change'
-- create_table("names",{:force=>true})
-> 0.0100s
-- initialize_schema_migrations_table()
-> 0.0025s
-- assume_migrated_upto_version(20130417185814,["/path/project/db/migrate"])
-> 0.0010s
You have 1 pending migrations:
20130417185845 CreateNames
Run `rake db:migrate` to update your database then try again.
也许,我做错了什么？迁移具有删除表的代码 – 它是否仅用于回滚？
解
>创建模型：rails g model用户名
>迁移：rake db：migrate
>实现一些东西,突然想起你需要删除模型
>恢复特定迁移：rake db：migrate：down VERSION = 20130417185814,其中20130417185814是迁移ID(可以在rake db：migrate：status中看到)
>删除模型：rails d model user
>突然想起你需要这个模型,但是需要其他领域
>创建模型：rails g model用户电子邮件组：引用
>成功迁移数据库：rake db：migrate