添加jsonapi-suite后出现未初始化常量错误，如何启用ActiveRecord适配器？

在现有Rails 5.2.0项目中添加jsonapi-suite相关Gem后，执行$ curl localhost:3001/groups返回如下错误：

ActionController::RoutingError (uninitialized constant JsonapiCompliable::Adapters::ActiveRecord): app/resources/application_resource.rb:9:in `<class:ApplicationResource>' app/resources/application_resource.rb:5:in `<main>' app/resources/group_resource.rb:1:in `<main>' app/controllers/groups_controller.rb:3:in `<class:GroupsController>' app/controllers/groups_controller.rb:1:in `<main>'

项目相关配置代码 #

Gemfile

gem 'jsonapi_suite', '~> 0.7'
gem 'jsonapi-rails', '~> 0.3.0'
gem 'jsonapi_swagger_helpers', '~> 0.6', require: false
gem 'jsonapi_spec_helpers', '~> 0.4', require: false
gem 'kaminari', '~> 1.0'

ApplicationController

class ApplicationController < ActionController::API
+ # Bootstrap jsonapi_suite with relevant modules
+ include JsonapiSuite::ControllerMixin
+
+ register_exception JsonapiCompliable::Errors::RecordNotFound,
+ status: 404
+
+ # Catch all exceptions and render a JSONAPI-compliable error payload
+ # For additional documentation, see https://jsonapi-suite.github.io/jsonapi_errorable
+ rescue_from Exception do |e|
+ handle_exception(e)
+ end
+

GroupsController

class GroupsController < ApplicationController
  jsonapi resource: GroupResource
  strong_resource :group
  before_action :apply_strong_params, only: [:create, :update]

  def index
    groups = Group.all
    render_jsonapi(groups)
  end

  def show
    scope = jsonapi_scope(Group.where(id: params[:id]))
    instance = scope.resolve.first
    raise JsonapiCompliable::Errors::RecordNotFound unless instance
    render_jsonapi(instance, scope: false)
  end

  def create
    group, success = jsonapi_create.to_a
    if success
      render_jsonapi(group, scope: false)
    else
      render_errors_for(group)
    end
  end

  def update
    group, success = jsonapi_update.to_a
    if success
      render_jsonapi(group, scope: false)
    else
      render_errors_for(group)
    end
  end

  def destroy
    group, success = jsonapi_destroy.to_a
    if success
      render json: { meta: {} }
    else
      render_errors_for(group)
    end
  end
end

app/resources/group_resource.rb

class GroupResource < ApplicationResource
  type :groups
end

控制台调试结果

[4] pry(main)> JsonapiCompliable::Adapters
=> JsonapiCompliable::Adapters
[5] pry(main)> JsonapiCompliable::Adapters::ActiveRecord
NameError: uninitialized constant JsonapiCompliable::Adapters::ActiveRecord

app/resources/application_resource.rb

class ApplicationResource < JsonapiCompliable::Resource
  use_adapter JsonapiCompliable::Adapters::ActiveRecord
end

请问为何JsonapiCompliable::Adapters::ActiveRecord不可用，如何使其可用？

原因分析 #

这个错误的核心问题很明确：jsonapi_compliable的ActiveRecord适配器没有被加载。从jsonapi_suite 0.7版本开始，官方把不同ORM的适配器拆成了独立的Gem包，默认不会自动引入ActiveRecord适配器，所以你的代码找不到这个常量。

解决办法 #

1. 补充ActiveRecord适配器Gem #

打开你的Gemfile，添加专门的ActiveRecord适配器Gem（版本号建议和jsonapi_suite保持一致，避免兼容性问题）：

gem 'jsonapi_compliable-active_record', '~> 0.7'

2. 安装并重启服务 #

执行bundle命令安装新Gem：

bundle install

然后必须重启你的Rails服务器——新Gem只有在服务器重启后才会被加载生效。

3. 验证修复效果 #

重启后打开rails控制台，再次尝试调用这个常量：

[1] pry(main)> JsonapiCompliable::Adapters::ActiveRecord

如果返回JsonapiCompliable::Adapters::ActiveRecord而不是报错，说明问题已经解决。此时再请求localhost:3001/groups应该就能正常返回数据了。

备选方案（不推荐） #

如果你不想添加额外的Gem，可以手动在代码里require适配器文件。比如在app/resources/application_resource.rb开头加上：

require 'jsonapi_compliable/adapters/active_record'

不过这种方式不推荐，因为后续版本更新可能会改变文件路径，导致代码出错，还是用官方提供的独立Gem更稳妥。

内容的提问来源于stack exchange，提问作者martins