rails database.yml 不接受 ERB

Question

在我的 database.yml 中，我有：

staging:
  adapter: <%= ENV['DATABASE_ADAPTER'] %>
  encoding: <%= ENV['DATABASE_ENCODING'] %>
  database: <%= ENV['DATABASE'] %>
  host: <%= ENV['DATABASE_HOST'] %>
  port: <%= ENV['DATABASE_PORT'].to_i %>
  pool: <%= ENV['DATABASE_POOL'].to_i %>
  username: <%= ENV['DATABASE_USERNAME'] %>
  password: <%= ENV['DATABASE_PASSWORD'] %>

但是，它在实际启动 puma 时不会读取 ERB 部分：

/usr/local/lib/ruby/gems/2.1.0/gems/activesupport-4.2.1/lib/active_support/dependencies.rb:274:in 
`require': Could not load 'active_record/connection_adapters/<%= ENV['DATABASE_ADAPTER'] %>_adapter'. 
Make sure that the adapter in config/database.yml is valid. If you use an adapter other than 'mysql', 'mysql2', 'postgresql' or 'sqlite3'
add the necessary adapter gem to the Gemfile. (LoadError)

这没有任何意义，因为在 Rails 代码中加载数据库配置：

  def database_configuration
    yaml = Pathname.new(paths["config/database"].existent.first || "")

    config = if yaml.exist?
      require "yaml"
      require "erb"
      YAML.load(ERB.new(yaml.read).result) || {}
    elsif ENV['DATABASE_URL']
      # Value from ENV['DATABASE_URL'] is set to default database connection
      # by Active Record.
      {}
    else
      raise "Could not load database configuration. No such file - #{yaml}"
    end

    config
  rescue Psych::SyntaxError => e
    raise "YAML syntax error occurred while parsing #{paths["config/database"].first}. " \
          "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
          "Error: #{e.message}"
  rescue => e
    raise e, "Cannot load `Rails.application.database_configuration`:\n#{e.message}", e.backtrace
  end

（取自 Rails 4.2 稳定代码，我运行的是 4.2.1）

我非常困惑为什么这不起作用，有什么想法吗？

Answer 1

我刚刚经历了同样的事情，并看到了你的帖子。我一直在关注一个教程，该教程让我创建了一个 puma.conf 文件，其中包含以下代码：

ActiveRecord::Base.establish_connection( YAML.load_file( "#{app_dir}/config/database.yml" )[rails_env])

我修改了以下内容，一切都按预期工作：

require 'erb'
ActiveRecord::Base.establish_connection( YAML.load( ERB.new( File.read( "#{app_dir}/config/database.yml" )).result)[rails_env])