Ruby-on-rails 无法加载`Rails.application.database_configuration`：未知别名：默认

Cannot load `Rails.application.database_configuration`: Unknown alias: default

提问by user3868747

I am new to Ruby on Rails and I am guessing that the answer to my question is pretty simple but I can't find it. I recently created a project and used "rails generate scaffold..." and everything was working fine. I wanted to add another column to the database so I used "rails generate migration ...." Everything worked well after this too. The problem started after I stopped the server and restarted it. Now I get this error Psych::BadAlias Cannot load Rails.application.database_configuration: Unknown alias: default

我是 Ruby on Rails 的新手，我猜我的问题的答案很简单，但我找不到。我最近创建了一个项目并使用了“rails generate scaffold...”并且一切正常。我想向数据库添加另一列，所以我使用了“rails generate migration ....”之后一切都运行良好。在我停止服务器并重新启动它后问题就开始了。现在我收到此错误 Psych::BadAlias 无法加载Rails.application.database_configuration：未知别名：默认

I found this Requesting a ruby-on-rails application gives Psych::BadAlias errorbut I didn't see a definite answer.

我发现这个请求 ruby​​-on-rails 应用程序给出了 Psych::BadAlias 错误，但我没有看到明确的答案。

Here is what my database.yml file looks like...

这是我的 database.yml 文件的样子...

  #  

  <<: *default 
    database: db/development.sqlite3 


  test:
    <<: *default
    database: db/development.sqlite3_test

  production:
    <<: *default  
    database: db/development.sqlite3_production 

Here is the file that genereated after I did the migration

这是我迁移后生成的文件

class AddHardwareToComputers < ActiveRecord::Migration
  def change
    add_column :computers, :hardware, :string
  end
end

and here is my schema.rb

这是我的 schema.rb

ActiveRecord::Schema.define(version: 20140723203054) do  

  create_table "computers", force: true do |t|
    t.string   "name"
    t.string   "serial_number"
    t.string   "user"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "hardware" 
  end

end

Any help would be appreciated. Thank you.

任何帮助，将不胜感激。谢谢你。

回答by hgorni

I know this is an old question but I was looking for the same issue and got it resolved using jvnill's + CocoHot's suggestion with a small correction. I don't have enough points to comment so I'm adding the amended solution as a new answer.

我知道这是一个老问题，但我一直在寻找同样的问题，并使用 jvnill 的 + CocoHot 的建议解决了这个问题，并稍作修正。我没有足够的分数来评论，所以我将修改后的解决方案添加为新答案。

First, change &defaultsto &default(singular); second, since you are using sqlite3 (as I am), replace the adapter mysql2with sqlite3.

首先，变化&defaults到&default（单数）; 第二，因为你正在使用sqlite3的（如我），更换适配器mysql2使用sqlite3。

defaults: &default
  adapter: sqlite3
  encoding: utf8

development:
  <<: *default
  database: db/development.sqlite3

test:
  <<: *default
  database: db/development.sqlite3_test

production:
  <<: *default
  database: db/development.sqlite3_production

回答by jvnill

your yaml file should contain a configuration that's default like the following

您的 yaml 文件应包含一个默认配置，如下所示

defaults: &default
  adapter: mysql2
  encoding: utf8

development:
  <<: *default
  database: app_development

test:
  <<: *default
  database: app_test

EDIT: Apr 22, 2020

编辑：2020 年 4 月 22 日

• change defaultsto defaultto make it less confusing.

• 更改defaults为default使其不那么混乱。

回答by CocoHot

jvnill's point on the right path

jvnill 在正确的道路上的点

All you need is change it to default: &defaultinstead of defaults: &defaultsand you should be good.

您所需要的只是将其更改为default: &default而不是，defaults: &defaults您应该会很好。

回答by ImranNaqvi

I found a different case , actually i merged my old code with openshift's new code . And it generated two defaults and two development modes in the database.yml file . I just removed the duplicates and made my Yaml file look like below . and it worked (i'm pasting my yaml file for the sake of reference)

我发现了一个不同的案例，实际上我将旧代码与 openshift 的新代码合并了。并且在database.yml 文件中生成了两个默认值和两种开发模式。我刚刚删除了重复项并使我的 Yaml 文件如下所示。它起作用了（我正在粘贴我的 yaml 文件以供参考）

development:
  adapter: mysql2
  encoding: utf8
  pool: 5
  username: root
  password: admin
  database: abc
  timeout: 5000

production:  
  adapter: mysql2
  database: <%=ENV['OPENSHIFT_APP_NAME']%>
  username: <%=ENV['OPENSHIFT_MYSQL_DB_USERNAME']%>
  password: <%=ENV['OPENSHIFT_MYSQL_DB_PASSWORD']%>
  host:     <%=ENV['OPENSHIFT_MYSQL_DB_HOST']%>
  port:     <%=ENV['OPENSHIFT_MYSQL_DB_PORT']%>
  min_messages: ERROR
  reconnect: false

As both of my enviroments required difference confs , so i removed the default case at all and defined individual case as you can see . It'll be good for some one to give it a shot when very desperate , i mean by removing default cases at all

由于我的两个环境都需要不同的 confs，所以我完全删除了默认情况并定义了个别情况，如您所见。有人在非常绝望的时候试一试会很好，我的意思是完全删除默认情况