Rails Service Object with Dry-Monad yielding early

Support
1

I have a couple of service objects in my rails application where I am using Dry-Monads to influence a pattern of “success” or “failure” by using their Do Notation. However, in my main service object, upon calling a secondary service object, the main class returns early instead of following down to the last success call.

ApplicationService

# frozen_string_literal: true

require 'dry/monads'

class ApplicationService
  include Dry::Monads[:result, :do]

  def self.call(*args, **kwargs, &block)
    new(*args, **kwargs, &block).call
  end

  def success!(val = nil)
    Success(val)
  end

  def fail!(err)
    Failure(err)
  end
end

Create Check Request

class CheckRequests::Create < ApplicationService
  attr_accessor :user, :params, :company, :check_request

  def initialize(user:, params:)
    @user = user
    @check_request = nil
    @company = find_company(params[:company_id])
    @params = set_default_params(params)
  end

  def call
    # Calling this service class seems to yield right here
    vendor_id = yield generate_vendor_id
    check_request = yield create_check_request(vendor_id)

    success!({ check_request: check_request })
  end

  private

  def create_check_request(vendor_id)
    params[:vendor_id] = vendor_id if vendor_id.present?
    success!(CheckRequest.create!(**params))
  rescue ActiveRecord::RecordInvalid => e
    fail!(e.record.errors)
  end

  def find_company(company_id)
    Company.find(company_id)
  rescue ActiveRecord::RecordNotFound => e
    fail!("Cannot find company with id #{company_id}")
  end

  def set_default_params(params)
    params = params.dup
    approved = params[:status] == 'Approved'
    params[:source_account_id] = company.default_source_account
    if approved
      params[:approved_at] = DateTime.now
      params[:approver] = user
    end

    params
  end

  def generate_vendor_id
    return success! unless vendor_needed?
    vendor_uniq = ::Quickbooks::Query.unique(company, params[:client])
    return success! unless vendor_uniq

    Qbo::Vendors::Create.new(
      company: company,
      client: params[:client],
      mailing_address: JSON.parse(params[:mailing_address])
    ).call
  end

  def vendor_needed?
    params[:vendor_id] == '0'
  end
end

Vendor Create Service Object

class Qbo::Vendors::Create < ApplicationService
  attr_accessor :company, :client, :mailing_address

  def initialize(company:, client:, mailing_address:)
    @company = company
    @client = client
    @mailing_address = mailing_address
  end

  def call
    yield create_qbo_vendor
  end

  private

  def create_qbo_vendor
    url = "#{ENV["QBO_BASE_URL"]}company/#{company.realm_id}/vendor"
    response = RestClient.post(
      url,
      { DisplayName: client, BillAddr: mailing_address }.to_json,
      {
        Authorization: "Bearer #{company.access_token}",
        content_type: "application/json"
      }
    )
    vendor = Hash.from_xml(response.body)
    success!(vendor.dig("IntuitResponse", "Vendor", "Id"))
  rescue RestClient::ExceptionWithResponse => e
    body = JSON.parse(e.http_body)
    err = body.dig("Fault", "Error", 0, "Detail") || e.message
    fail!(err)
  end
end

I’m sure I am just not looking at things correctly. Any and all help would be greatly appreciated!

2

Here’s the thing with your code, it doesn’t quite follow the rule where if a method returns Success/Failure in one path it must return Success/Failure in all other cases.
For instance,

  def find_company(company_id)
    Company.find(company_id)
  rescue ActiveRecord::RecordNotFound => e
    fail!("Cannot find company with id #{company_id}")
  end

It either returns a Company or a Failure. It must not. The code should look like

  def find_company(company_id)
    success!(Company.find(company_id))
  rescue ActiveRecord::RecordNotFound => e
    fail!("Cannot find company with id #{company_id}")
  end

Another case:

  def call
    yield create_qbo_vendor
  end

Currently, it returns a Failure if create_qbo_vendor returns a Failure or some value from vendor. Remember, yield unwraps Successes, it must end with a value:

  def call
    result = yield create_qbo_vendor

    success!(result)
  end

or, simply

  def call
    create_qbo_vendor
  end

First of all, you’ll need to correct all such places. Practically, such requirements are not so restricting, once you get the idea, writing code in that way becomes a habit.

3

@flash-gordon thanks for the quick reply! I have changed my code to reflect the changes you mentioned

class Qbo::Vendors::Create < ApplicationService
  attr_accessor :company, :client, :mailing_address

  def initialize(company:, client:, mailing_address:)
    @company = company
    @client = client
    @mailing_address = mailing_address
  end

  def call
    create_qbo_vendor
  end

  private

  def create_qbo_vendor
    url = "#{ENV["QBO_BASE_URL"]}company/#{company.realm_id}/vendor"
    response = RestClient.post(
      url,
      { DisplayName: client, BillAddr: mailing_address }.to_json,
      {
        Authorization: "Bearer #{company.access_token}",
        content_type: "application/json"
      }
    )
    vendor = Hash.from_xml(response.body)
    success!(vendor.dig("IntuitResponse", "Vendor", "Id"))
  rescue RestClient::ExceptionWithResponse => e
    body = JSON.parse(e.http_body)
    err = body.dig("Fault", "Error", 0, "Detail") || e.message
    fail!(err)
  end
end

class CheckRequests::Create < ApplicationService
  attr_accessor :user, :params, :company, :check_request

  def initialize(user:, params:)
    @user = user
    @check_request = nil
    @company = yield find_company(params[:company_id])
    @params = yield set_default_params(params)
  end

  def call
    vendor_id = yield generate_vendor_id
    check_request = yield create_check_request(vendor_id)

    success!({ check_request: check_request })
  end

  private

  def create_check_request(vendor_id)
    params[:vendor_id] = vendor_id if vendor_id.present?
    success!(CheckRequest.create!(**params))
  rescue ActiveRecord::RecordInvalid => e
    fail!(e.record.errors)
  end

  def find_company(company_id)
    success!(Company.find(company_id))
  rescue ActiveRecord::RecordNotFound => e
    fail!("Cannot find company with id #{company_id}")
  end

  def set_default_params(params)
    params = params.dup
    approved = params[:status] == 'Approved'
    params[:source_account_id] = company.default_source_account
    if approved
      params[:approved_at] = DateTime.now
      params[:approver] = user
    end

    success!(params)
  end

  def generate_vendor_id
    return success! unless vendor_needed? || !vendor_uniq?
    Qbo::Vendors::Create.new(
      company: company,
      client: params[:client],
      mailing_address: JSON.parse(params[:mailing_address])
    ).call
  end

  def vendor_needed?
    params[:vendor_id] == '0'
  end

  def vendor_uniq?
    ::Quickbooks::Query.unique(company, params[:client])
  end
end

But now, when #call is called on the CheckRequests::Create class, the method simply returns the ID of the generated vendor, vs flowing down the rest of the method. What might be causing this code to short circuit early?

4

Ok, I changed out my code to try to isolate the API call to be inside the single service object.

class CheckRequests::Create < ApplicationService
  attr_accessor :user, :params, :company, :check_request

  def initialize(user:, params:)
    @user = user
    @check_request = nil
    @company = yield find_company(params[:company_id])
    @params = yield set_default_params(params)
  end

  def call
    vendor_id = yield create_qbo_vendor(
      company: company,
      client: params[:client],
      mailing_address: JSON.parse(params[:mailing_address])
    )
    check_request = yield create_check_request(vendor_id)

    success!({ check_request: check_request })
  end

  private

  def create_check_request(vendor_id)
    params[:vendor_id] = vendor_id if vendor_id.present?
    success!(CheckRequest.create!(**params))
  rescue ActiveRecord::RecordInvalid => e
    fail!(e.record.errors)
  end

  def find_company(company_id)
    success!(Company.find(company_id))
  rescue ActiveRecord::RecordNotFound => e
    fail!("Cannot find company with id #{company_id}")
  end

  def set_default_params(params)
    params = params.dup
    approved = params[:status] == 'Approved'
    params[:source_account_id] = company.default_source_account
    if approved
      params[:approved_at] = DateTime.now
      params[:approver] = user
    end

    success!(params)
  end

  def create_qbo_vendor(client:, company:, mailing_address:)
    return success! unless vendor_needed?
    return success! unless vendor_uniq?

    url = "#{ENV["QBO_BASE_URL"]}company/#{company.realm_id}/vendor"
    response = RestClient.post(
      url,
      { DisplayName: client, BillAddr: mailing_address }.to_json,
      {
        Authorization: "Bearer #{company.access_token}",
        content_type: "application/json"
      }
    )
    vendor = Hash.from_xml(response.body)
    success!(vendor.dig("IntuitResponse", "Vendor", "Id"))
  rescue RestClient::ExceptionWithResponse => e
    body = JSON.parse(e.http_body)
    err = body.dig("Fault", "Error", 0, "Detail") || e.message
    fail!(err)
  end

  def vendor_needed?
    params[:vendor_id].to_i.zero?
  end

  def vendor_uniq?
    ::Quickbooks::Query.unique(company, params[:client])
  end
end

And its still exiting early when calling yield create_qbo_vendor. I fetch the success or failure like so:

# api/check_requests_controller.rb
def create
  response = CheckRequests::Create.new(user: current_user, params: check_request_params)
  handle_service_response(response)
end

# application_controller.rb
  def handle_service_response(service, **kwargs)
    service.call do |result|
      if result.success?
        response.header['Location'] = kwargs.delete(:location)
        render(json: result.value!) and return
      else
        render(json: { errors: result.failure }, status: :unprocessable_entity) and return
      end
    end
  end
5

Here’s the problem. You can’t pass a block to a method that uses do notation.
Specifically, this is wrong because the call method relies on yield passed automagically by include Dry::Monads[:result, :do]

    service.call do |result|
      if result.success?
        response.header['Location'] = kwargs.delete(:location)
        render(json: result.value!) and return
      else
        render(json: { errors: result.failure }, status: :unprocessable_entity) and return
      end
    end

It’s allowed to pass user blocks only to methods that don’t use yield for chaining Result values. Unfortunately, it’s not possible for dry-monads to distinguish if a method expects do notation or just yields a block.

Your code should be changed to

# using ruby 3.1+
# application_controller.rb
include Dry::Monads[:result] # import Success/Failure constants

def handle_service_response(service, **kwargs)
  case service.call
  in Success(json)
    response.header['Location'] = kwargs.delete(:location)
    render(json:)
  in Failure(errors)
    render(json: { errors: }, status: :unprocessable_entity)
  end
end