aborted destroy turned into JSONAPI::Exceptions::ValidationErrors without error message

从 JR 处理器的 process 方法以及 lib/jsonapi/resource.rb 第 224-231 行附近开始，issue 指出这些位置与模型错误消息有关。复现一个会 throw :abort 的 Rails destroy 回调，然后追踪空错误如何到达 ValidationErrors。完成标准是：被中止的 destroy 产生可用的验证错误，而不是因缺少 code 导致的 NoMethodError。

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• Problem/bug report.
• Feature request.
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• I've searched for an existing issue.
• I've asked my question on Gitter and have not received a satisfactory answer.
• I've included a complete bug report template. This step helps us and allows us to see the bug without trying to reproduce the problem from your description. It helps you because you will frequently detect if it's a problem specific to your project.
• The feature I'm asking for is compliant with the JSON:API spec.

Description

Choose one section below and delete the other:

Bug reports:

JR version 0.9.3

1. Given a record with before_destroy :something_that_may_abort
2. Define def something_that_may_abort; throw :abort if condition?; end
3. POST a DELETE by id to the corresponding resource
4. Get

   NoMethodError: undefined method `code' for nil:NilClass

The problem stems from the JR processor

    def process
      run_callbacks :operation do
        run_callbacks operation_type do
          @result = send(operation_type)
        end
      end

    rescue JSONAPI::Exceptions::Error => e
      @result = JSONAPI::ErrorsOperationResult.new(e.errors[0].code, e.errors)
    end

Where the rescued JSONAPI::Exceptions::Error is a JSONAPI::Exceptions::ValidationErrors and the error_messages attribute is an empty hash. This can be observed in Rails code as

record.destroy
=> false
 record.errors.messages
=> {}

I suspect this isn't an altogether unusual case. Until this is addressed in JR, I'm looking at handling this by adding validation errors to the model before throwing the abort

Proposal

I wonder if there may be a place in JR to add a default validation error message to JSONAPI::Exceptions::ValidationErrors when none are given (i.e. when resource.model_error_messages is empty

https://github.com/cerebris/jsonapi-resources/blob/v0.9.7/lib/jsonapi/resource.rb#L224-L231