錯誤遷移DB Rails的

Question

我試着去使用這種遷移，但我不斷收到錯誤，像這些

這是我的移民文件

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 

當我嘗試執行耙分貝：遷移得到這個錯誤：

== 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

正如我寫的評論，您收到因爲這個錯誤：

SQLite3::SQLException: table "employees" already exists 

這意味着您已經在數據庫中擁有該列。您可以解決在幾個方面：

• 改變遷移修改，而不是創造：

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

• 添加另一個遷移將下降全表（顯然，一個人應該比前面的時間戳從控制檯手

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

• 降表，但是這並不是一個非常：修改一個這樣的表將首先被再度回落，然後創建）不錯的選擇，因爲你應該學習使用遷移來改變你的數據庫，當然這將是最快的一個（如果你知道如何使用控制檯）並且不會造成任何傷害，但如果這只是一些學習項目，儘可能地學習良好的習慣。

你也可能需要使用新的語法（據我所知）的def change代替self.up和self.down，少字母鍵入並減少重複;）

Answer 2

你跑了，移民已經在它的錯誤。所以遷移進行到一半，創建表不完整。回滾該遷移，然後再次運行遷移。

Answer 3

您的員工表已經創建在您的數據庫中。你需要修復它，那麼你可以做到這一點有兩種方式1.降數據庫，並創建一個或多個2.運行向下遷移然後向上遷移

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