对我来说,创建模型、运行迁移、销毁模型,再次创建相同的模型时出现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?迁移有删除表的代码 - 它只能用于回滚吗?
解决方法
删除模型和数据库表并生成一个新的相当容易:
1. 创建模型:
rails g model user name
2. 执行迁移:rake db:migrate
3. 在实现某些功能时,突然想起需要删除模型
4. 回滚到特定的迁移:rake db:migrate:down VERSION=20130417185814
,其中20130417185814
是迁移 ID(可以在rake db:migrate:status
中看到)
5. 删除模型:rails d model user
6. 突然想起需要该模型,但是带有其他字段
7. 创建模型:rails g model user email group:references
8. 成功迁移数据库:rake db:migrate
rake db:migrate:down VERSION=20130417185845
。谢谢 :) - Drakmail