Ruby on rails 迁移DB Rails时出错

我正在尝试使用这个迁移，但是我不断得到错误，就像下面这些

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

class CreateEmployeestrue
t、 整数：假期天数
t、 案文：评论
终止
终止
def自动关闭
下拉列表：员工
终止
终止

当我尝试执行rake db:migrate时，会出现以下错误：

==CreateEmployees:正在迁移================================================ --创建表格（：employees）rake中止！发生错误，此迁移和所有后续迁移已取消：

SQLite3:：SQLException:表“employees”已存在：创建表 “雇员”（“id”整数主键自动递增不为空，“名称” varchar（255），“雇佣”日期，“工资”浮动，“全职”布尔值 默认值为“t”，“vacationdays”整数，“comments”文本） /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

execute' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/sqlite3\u adapter.rb:328:in

block in execute'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/abstract\u adapter.rb:425:in

block in log' /Library/Ruby/Gems/2.0.0/Gems/activesupport-4.0.0/lib/active\u support/notifications/instrumenter.rb:20:in

仪器'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/abstract\u adapter.rb:420:in

log' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/sqlite3\u adapter.rb:328:in

execute'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/abstract/schema\u statements.rb:190:in

create_table' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:625:in

方法中的块\u缺失'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:597:in

用“时间”阻塞 /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:597:in

用“时间”说“时间”
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:617:in

方法\u缺失' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:383:in

method\u missing'/Users/YuriAguirre/Documents/Aptana Studio 3
Workspace/company/db/migrate/20130923140626\u create\u employees.rb:3:in

up' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:534:in

up'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:574:in

exec\u迁移' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:555:in 迁移中的块（2个级别）

/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:554:in

migrate中的块' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/abstract/connection\u pool.rb:294:in

与_连接'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:553:in

migrate' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:709:in

migrate'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:959:in

在事务中执行迁移时阻塞 /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:1005:in ddl_事务中的

块'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/abstract/database\u statements.rb:202:in

在事务中阻塞' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/abstract/database\u statements.rb:210:in

在新交易中
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/connection\u adapters/abstract/database\u statements.rb:202:in

transaction' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active_record/transactions.rb:209:in

transaction'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:1005:in

ddl\U交易' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:958:in

在\u事务中执行\u迁移\u'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:920:in

migrate中的块' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:916:in

每个'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:916:in

migrate' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:764:in

up'
/Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/migration.rb:742:in

migrate' /Library/Ruby/Gems/2.0.0/Gems/activerecord-4.0.0/lib/active\u record/railties/databases.rake:42:in `“Tasks:TOP=>db:migrate”中的块（2个级别）（请参见 通过使用--trace运行任务完成完整跟踪

---

正如我在评论中所写，您收到该错误是因为：

SQLite3::SQLException: table "employees" already exists

这意味着数据库中已经有了该列。您可以通过以下几种方式解决此问题：

• 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
  

  class CreateEmployees class RemoveEmployees < ActiveRecord::Migration
     def change
       drop_table :employees
     end
   end
  

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

  rails db:rollback
  rails db:migrate