YAML.load_file 无法正确读取 ENV 变量

Question

我已经设置了一个辅助数据库 YAML 文件，如下所示：

# config/remote_database.yml

default: &default
  adapter: postgresql
  encoding: unicode
  pool: 5

development:
  <<: *default
  database: 'cexplorer'
  username: <%= ENV['HOST_PG_DATABASE_USERNAME'] %>
  password: <%= ENV['HOST_PG_DATABASE_PASSWORD'] %>
  host: <%= ENV['HOST_PG_DATABASE_IP'] %>
  port: 5432

此 YAML 文件是从创建变量以用于establish_connection 的初始化程序中读取的：

# config/initializers/remote_database.rb

REMOTE_DB = YAML.load_file(File.join(Rails.root, "config", "remote_database.yml"))[Rails.env.to_s]

当我使用byebug 检查 REMOTE_DB 的外观时，我看到 ENV 变量是使用占位符而不是变量本身读取的，即使变量可用。

# app/models/remote_record.rb

class RemoteRecord < ActiveRecord::Base
  byebug
  establish_connection REMOTE_DB
end

[1, 5] in /Users/sergio/Documents/github/swan-to-db-sync-backend/app/models/db_sync_record.rb
   1: class RemoteRecord < ActiveRecord::Base
   2:   byebug
=> 3:   establish_connection DB_SYNC_DB
   4:   # REMOTE_DB is defined in `config/initializers/db_sync_database.rb`
   5: end
(byebug) REMOTE_DB
{"adapter"=>"postgresql", "encoding"=>"unicode", "pool"=>5, "database"=>"cexplorer", "username"=>"<%= ENV['HOST_PG_DATABASE_USERNAME'] %>", "password"=>"<%= ENV['HOST_PG_DATABASE_PASSWORD'] %>", "host"=>"<%= ENV['HOST_PG_DATABASE_IP'] %>", "port"=>"5432"}
(byebug) ENV['HOST_PG_DATABASE_USERNAME']
"postgres"
(byebug) 

如何在 REMOTE_DB 中获取实际的 ENV 变量值？

Answer 1

Pure YAML 对 ERB 语法一无所知，并且在加载文件时不会自动解释它。

这令人困惑，因为在 Ruby on Rails 中，这似乎适用于所有 YAML 配置文件。但它只起作用，因为 Ruby 在内部做了一些魔法。

当您想要加载 YAML 文件并动态解释该文件中的 ERB 时，您需要将 YAML 加载代码更改为如下内容：

file = File.read(Rails.root.join("config", "remote_database.yml"))
yaml = ERB.new(file).result

REMOTE_DB = YAML.load(yaml)[Rails.env.to_s]

Answer 2

Ruby YAML 模块不通过 ERB 传递文件。这实际上是 ActionSupport::ConfigurationFile. 的 Rails 特定功能

# frozen_string_literal: true

module ActiveSupport
  # Reads a YAML configuration file, evaluating any ERB, then
  # parsing the resulting YAML.
  #
  # Warns in case of YAML confusing characters, like invisible
  # non-breaking spaces.
  class ConfigurationFile # :nodoc:
    class FormatError < StandardError; end

    def initialize(content_path)
      @content_path = content_path.to_s
      @content = read content_path
    end

    def self.parse(content_path, **options)
      new(content_path).parse(**options)
    end

    def parse(context: nil, **options)
      YAML.load(render(context), **options) || {}
    rescue Psych::SyntaxError => error
      raise "YAML syntax error occurred while parsing #{@content_path}. " \
            "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
            "Error: #{error.message}"
    end

    private
      def read(content_path)
        require "yaml"
        require "erb"

        File.read(content_path).tap do |content|
          if content.include?("\u00A0")
            warn "#{content_path} contains invisible non-breaking spaces, you may want to remove those"
          end
        end
      end

      def render(context)
        erb = ERB.new(@content).tap { |e| e.filename = @content_path }
        context ? erb.result(context) : erb.result
      end
  end
end

所以你可以解析一个配置文件：

@config = ActiveSupport::ConfigurationFile.parse(path_to_file)

ActiveRecord 实际上还有一些技巧，它将 YAML 配置与 ENV['DATABASE_URL'] 合并。

但是你实际上并不需要它。在 Rails 6+ 中你实际上可以define multiple databases per environment:

development:
  primary:
    database: my_development_database
    adapter: mysql
  remote:
    database: my_primary_database
    host: somehost
    adapter: mysql

在任何以前的版本中，您都可以创建更多环境，例如临时环境或使用ENV['DATABASE_URL'] 到supplement/override the YAML configuration。