Question

我试图使用此迁移，但我不断收到错误，例如

这是我的迁移文件

class CreateEmployees < ActiveRecord::Migration
  def self.up
    create_table :employees do |t|
      t.string :name 
      t.date :hiredate 
      t.float :salary 
      t.boolean :fulltime , :default => true 
      t.integer :vacationdays 
      t.text :comments
    end 
  end

  def self.down
    drop_table :employees
  end
end

当我尝试执行rake db：migrate时出现此错误：

== CreateEmployees：迁移========================================== ======    - create_table（：employees）rake aborted！发生错误，此操作和所有后续迁移都已取消：

SQLite3 :: SQLException：表“employees”已经存在：CREATE TABLE   “雇员”（“id”INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL，“name”   varchar（255），“hiredate”date，“salary”float，“fulltime”boolean   DEFAULT't'，“休假日”整数，“评论”文字）   /Library/Ruby/Gems/2.0.0/gems/sql   ite3-1.3.8 / lib / sqlite3 / database.rb:91:in initialize' /Library/Ruby/Gems/2.0.0/gems/sqlite3-1.3.8/lib/sqlite3/database.rb:91:in new'   /Library/Ruby/Gems/2.0.0/gems/sqlite3-1.3.8/lib/sqlite3/database.rb:91:in   prepare' /Library/Ruby/Gems/2.0.0/gems/sqlite3-1.3.8/lib/sqlite3/database.rb:134:in执行”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/sqlite3_adapter.rb:328:in block in execute' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:425:in阻止日志'   /Library/Ruby/Gems/2.0.0/gems/activesupport-4.0.0/lib/active_support/notifications/instrumenter.rb:20:in   instrument' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:420:in登录”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/sqlite3_adapter.rb:328:in execute' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/schema_statements.rb:190:in create_table'   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:625:in   {_ 1}}阻止在say_with_time'   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:597:in   block in method_missing' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:597:in的method_missing”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:383:in   say_with_time' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:617:in向上”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:534:in   method_missing' /Users/YuriAguirre/Documents/Aptana Studio 3 Workspace/company/db/migrate/20130923140626_create_employees.rb:3:in exec_migration”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:555:in   up' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:574:in阻止迁移'   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in   block (2 levels) in migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:554:in迁移”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:709:in   execute_migration_in_transaction中的with_connection' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:553:in阻止   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:1005:in   交易migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:959:in阻止   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/database_statements.rb:210:in   block in ddl_transaction' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/database_statements.rb:202:in交易”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/transactions.rb:209:in within_new_transact ion' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/database_statements.rb:202:in ddl_transaction'   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:958:in   transaction' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:1005:in阻止迁移'   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:916:in   execute_migration_in_transaction' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:920:in迁移”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:764:in   each' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:916:in迁移”   /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/railties/databases.rake:42:in   '任务：TOP =＆gt;中的'阻止（2级） db：migrate（参见   使用--trace运行任务完全跟踪

Answer 1

您的员工表已在数据库中创建。您需要修复它，然后您可以通过两种方式执行此操作1.删除数据库并再创建一个或2.运行向下迁移然后向上迁移

rake db:drop
rake db:create
rake db:migrate

Answer 2

正如我在评论中写的那样，您收到的错误是因为：

SQLite3::SQLException: table "employees" already exists

这意味着您已经在数据库中拥有该列。您可以通过以下几种方式解决这个问题：

将迁移更改为修改而不是创建：

class CreateEmployees < ActiveRecord::Migration
  def self.up
    add_column :employees, :name, :string 
    (...)
    end 
  end

  def self.down
    remove_column :employees, :name
  end
end

添加另一个将删除整个表的迁移（显然，那个应该使用更早的时间戳而不是修改一个，因此表将首先被删除然后再次创建）：
```
 class RemoveEmployees < ActiveRecord::Migration
   def change
     drop_table :employees
   end
 end
```
从控制台手动删除表，但这不是一个很好的选择，因为您应该学会使用迁移来更改数据库，当然这是最快的（如果你知道如何使用控制台，如果这只是一些学习项目，那将不会造成伤害，但是，你应该尽可能地学习好习惯。

您可能还想使用较新的语法（AFAIK）def change而不是self.up和self.down，减少输入的字母数量，减少重复次数;）

Answer 3

您已经运行了该迁移，其中包含错误。因此迁移中途运行，不完全创建表。回滚该迁移，然后再次运行迁移。

Answer 4

您的迁移未完全运行。您应回滚迁移并再次迁移。

rails db:rollback
rails db:migrate

迁移DB Rails时出错

4 个答案: