错误迁移DB Rails的

Question

我试着去使用这种迁移，但我不断收到错误，像这些

这是我的移民文件

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 

当我尝试执行耙分贝：迁移得到这个错误：

== CreateEmployees: migrating ================================================ -- create_table(:employees) rake aborted! An error has occurred, this and all later migrations canceled:

SQLite3::SQLException: table "employees" already exists: CREATE TABLE "employees" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar (255), "hiredate" date, "salary" float, "fulltime" boolean DEFAULT 't', "vacationdays" integer, "comments" text) /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_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 block in log' /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 log' /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 block in method_missing' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:597:in block in say_with_time' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:597:in say_with_time' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:617:in method_missing' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:383:in method_missing' /Users/YuriAguirre/Documents/Aptana Studio 3 Workspace/company/db/migrate/20130923140626_create_employees.rb:3:in up' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:534:in up' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:574:in exec_migration' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:555:in block (2 levels) in migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:554:in block in migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:294:in with_connection' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:553:in migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:709:in migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:959:in block in execute_migration_in_transaction' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:1005: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 block in transactio n' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/database_statements.rb:210: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 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_record/migration.rb:1005:in ddl_transaction' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:958:in execute_migration_in_transaction' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:920:in block in migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:916:in each' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:916:in migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:764:in up' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/migration.rb:742:in migrate' /Library/Ruby/Gems/2.0.0/gems/activerecord-4.0.0/lib/active_record/railties/databases.rake:42:in `block (2 levels) in ' Tasks: TOP => db:migrate (See full trace by running task with --trace)

Answer 1

正如我写的评论，您收到因为这个错误：

SQLite3::SQLException: table "employees" already exists 

这意味着您已经在数据库中拥有该列。您可以解决在几个方面：

• 改变迁移修改，而不是创造：

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

• 添加另一个迁移将下降全表（显然，一个人应该比前面的时间戳从控制台手

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

• 降表，但是这并不是一个非常：修改一个这样的表将首先被再度回落，然后创建）不错的选择，因为你应该学习使用迁移来改变你的数据库，当然这将是最快的一个（如果你知道如何使用控制台）并且不会造成任何伤害，但如果这只是一些学习项目，尽可能地学习良好的习惯。

你也可能需要使用新的语法（据我所知）的def change代替self.up和self.down，少字母键入并减少重复;）

Answer 2

你跑了，移民已经在它的错误。所以迁移进行到一半，创建表不完整。回滚该迁移，然后再次运行迁移。

Answer 3

您的员工表已经创建在您的数据库中。你需要修复它，那么你可以做到这一点有两种方式1.降数据库，并创建一个或多个2.运行向下迁移然后向上迁移

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