Add support for extra_fields query parameter

Api now supports optional fields.
These are included with the extra_fields query param.

Syntax: extra_fields[type]=field1,field2

app/controllers/api/v1/base_controller.rb

@@ -106,7 +106,9 @@ module Api
       end
 
       def json_api_error(message, **options)
-        { errors: [{ detail: message }] }.merge(options)
+        error_options = options.delete(:error_options) || {}
+
+        { errors: [{ detail: message }.merge(error_options)] }.merge(options)
       end
 
       def json_api_invalid(message, errors)

app/controllers/concerns/extra_fields.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+# To be included in api controllers for handeling query params
+module ExtraFields
+  extend ActiveSupport::Concern
+
+  def invalid_query_param(name, status, msg)
+    render status: status, json: json_api_error(msg, error_options:
+      {
+        title: I18n.t("api.query_param.error.title"),
+        source: { parameter: name },
+        status: status,
+        code: Rack::Utils::SYMBOL_TO_STATUS_CODE[status]
+      })
+  end
+
+  def extra_fields(type, available_fields)
+    fields = params.dig(:extra_fields, type)&.split(',')&.compact&.map(&:to_sym)
+    return [] if fields.blank?
+
+    unknown_fields = fields - available_fields
+
+    if unknown_fields.present?
+      invalid_query_param(
+        "extra_fields[#{type}]", :unprocessable_entity,
+        I18n.t("api.query_param.error.extra_fields", fields: unknown_fields.join(', '))
+      )
+    end
+
+    fields
+  end
+end

config/locales/en.yml

@@ -1599,6 +1599,11 @@ en:
       destroy_attachment_does_not_exist: "Terms and Conditions file does not exist"
     orders:
       failed_to_update: "Failed to update order"
+    query_param:
+      error: 
+        title: Invalid query parameter
+        extra_fields: "Unsupported fields: %{fields}" 
+      
 
 # Frontend views
 #

spec/controllers/concerns/extra_fields_spec.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ExtraFields do
+  let(:dummy_controller) { Api::V1::BaseController.new.extend ExtraFields }
+
+  describe "#invalid_query_param" do
+    it "renders error" do
+      allow(dummy_controller).to receive(:render) {}
+      dummy_controller.invalid_query_param("param", :unprocessable_entity, "error message")
+      expect(dummy_controller).to have_received(:render).with(
+        json:
+          {
+            errors:
+            [{
+              code: 422,
+              detail: "error message",
+              source: { parameter: "param" },
+              status: :unprocessable_entity,
+              title: "Invalid query parameter"
+            }]
+          },
+        status: :unprocessable_entity
+      )
+    end
+  end
+
+  describe "#extra_fields" do
+    context "when fields present and available" do
+      it "returns extra fields" do
+        allow(dummy_controller).to receive(:params).
+          and_return({ extra_fields: { customer: "balance" } })
+        expect(dummy_controller.extra_fields(:customer, [:balance])).to eq([:balance])
+      end
+    end
+
+    context "when fields missing" do
+      it "returns empty arr" do
+        allow(dummy_controller).to receive(:params).and_return({})
+        expect(dummy_controller.extra_fields(:customer, [:balance])).to eq([])
+      end
+    end
+
+    context "when fields not in available fields" do
+      it "calls invalid_query_param" do
+        allow(dummy_controller).to receive(:invalid_query_param) {}
+        allow(dummy_controller).to receive(:params).
+          and_return({ extra_fields: { customer: "unknown" } })
+        dummy_controller.extra_fields(:customer, [:balance])
+
+        expect(dummy_controller).to have_received(:invalid_query_param).with(
+          "extra_fields[customer]",
+          :unprocessable_entity,
+          "Unsupported fields: unknown"
+        )
+      end
+    end
+  end
+end