#90

backend/app/controllers/application_controller.rb

@@ -1,4 +1,7 @@
 class ApplicationController < ActionController::API
+  rescue_from ActiveRecord::RecordInvalid, with: :render_record_invalid
+  rescue_from ActiveRecord::RecordNotUnique, with: :render_record_not_unique
+
   before_action :reject_banned_ip_address!
   before_action :authenticate_user
   before_action :reject_banned_user!
@@ -25,6 +28,42 @@ class ApplicationController < ActionController::API
     end
   end
 
+  def render_bad_request message = 'リクエストが不正です．', field: nil, code: :bad_request
+    render_error(:bad_request, message, field:, code:)
+  end
+
+  def render_unprocessable_entity message = '入力を確認してください．', field: nil, code: :invalid
+    render_error(:unprocessable_entity, message, field:, code:)
+  end
+
+  def render_error status, message, field: nil, code: status
+    error = { code: code.to_s, message: }
+    error[:field] = field.to_s if field.present?
+
+    render json: { errors: [error] }, status:
+  end
+
+  def render_model_errors record, status: :unprocessable_entity
+    errors =
+        record.errors.map do |error|
+          { code: error.type.to_s,
+            field: error.attribute.to_s,
+            message: error.full_message }
+        end
+
+    errors = [{ code: 'invalid', message: '入力を確認してください．' }] if errors.empty?
+
+    render json: { errors: }, status:
+  end
+
+  def render_record_invalid error
+    render_model_errors(error.record)
+  end
+
+  def render_record_not_unique _error = nil
+    render_unprocessable_entity('既に存在してゐます．', code: :taken)
+  end
+
   def reject_banned_ip_address!
     ip_address = IpAddress.find_by(ip_address: IPAddr.new(request.remote_ip).hton)
     return unless ip_address&.banned?
@@ -37,4 +76,28 @@ class ApplicationController < ActionController::API
 
     head :forbidden
   end
+
+  def render_validation_error record = nil, fields: { }, base: []
+    errors = { }
+
+    if record
+      record.errors.messages.each do |attr, messages|
+        errors[attr] ||= []
+        errors[attr].concat(messages)
+      end
+    end
+
+    fields.each do |attr, messages|
+      errors[attr] ||= []
+      errors[attr].concat(Array(messages))
+    end
+
+    base_errors = Array(base) - Array(errors.delete(:base))
+
+    render json: { type: 'validation_error',
+                   message: '入力内容を確認してください．',
+                   errors:,
+                   base_errors: },
+           status: :unprocessable_entity
+  end
 end