Add dynamic field support

lib/blueprinter/base.rb

@@ -11,6 +11,7 @@
 require_relative 'helpers/base_helpers'
 require_relative 'view'
 require_relative 'view_collection'
+require_relative 'transformer'
 
 module Blueprinter
   class Base
@@ -274,6 +275,43 @@ def self.fields(*field_names)
       end
     end
 
+
+
+    # Specify one transformer to be included for serialization.
+    # Takes a class which extends Blueprinter::Transformer
+    #
+    # @param class name [Class] which implements the method transform to include for
+    #   serialization.
+    #
+    #    
+    # @example Specifying a DynamicFieldTransformer transformer for including dynamic fields to be serialized.
+    #   class User 
+    #      def custom_columns
+    #         self.dynamic_fields #which is an array of some columns
+    #      end
+    #      def custom_fields
+    #         custom_columns.each_with_object({}){|col,result|  result[col] = self.send(col)}
+    #      end
+    #   end
+    #
+    #   class UserBlueprint < Blueprinter::Base
+    #     fields :first_name, :last_name
+    #     transform DynamicTransformer  
+    #     # other code
+    #   end
+    #
+    #   class DynamicFieldTransformer < Blueprinter::Transformer
+    #     def transform(hash, object, options)
+    #       hash.merge!(object.dynamic_fields)
+    #     end
+    #   end
+    #
+    # @return [Array<Class>] an array of transformers
+    def self.transform(transformer)
+      current_view.add_transformer(transformer)
+    end
+
+
     # Specify another view that should be mixed into the current view.
     #
     # @param view_name [Symbol] the view to mix into the current view.

lib/blueprinter/helpers/base_helpers.rb

@@ -44,10 +44,14 @@ def inherited(subclass)
       end
 
       def object_to_hash(object, view_name:, local_options:)
-        view_collection.fields_for(view_name).each_with_object({}) do |field, hash|
+        result_hash = view_collection.fields_for(view_name).each_with_object({}) do |field, hash|
           next if field.skip?(field.name, object, local_options)
-          hash[field.name] = field.extract(object, local_options)
+           hash[field.name] = field.extract(object, local_options)
         end
+        view_collection.transformers(view_name).each do |transformer|
+           transformer.transform(result_hash,object,local_options)
+        end
+        result_hash
       end
 
       def validate_root_and_meta(root, meta)

lib/blueprinter/transformer.rb

@@ -0,0 +1,12 @@
+module Blueprinter
+  # @api private
+  class Transformer
+    def transform(result_hash,primary_obj, options={})
+      fail NotImplementedError, "A Transformer must implement #transform"
+    end
+
+    def self.transform(result_hash,primary_obj, options={})
+      self.new.transform(result_hash,primary_obj, options)
+    end
+  end
+end

lib/blueprinter/view.rb

@@ -1,13 +1,14 @@
 module Blueprinter
   # @api private
   class View
-    attr_reader :excluded_field_names, :fields, :included_view_names, :name
+    attr_reader :excluded_field_names, :fields, :included_view_names, :name, :transformers
 
-    def initialize(name, fields: {}, included_view_names: [], excluded_view_names: [])
+    def initialize(name, fields: {}, included_view_names: [], excluded_view_names: [],transformers: [])
       @name = name
       @fields = fields
       @included_view_names = included_view_names
       @excluded_field_names = excluded_view_names
+      @transformers =  transformers
     end
 
     def inherit(view)
@@ -22,6 +23,10 @@ def inherit(view)
       view.excluded_field_names.each do |field_name|
         exclude_field(field_name)
       end
+
+      view.transformers.each do |transformer|
+        self.add_transformer(transformer)
+      end
     end
 
     def include_view(view_name)
@@ -38,6 +43,10 @@ def exclude_fields(field_names)
       end
     end
 
+    def add_transformer(custom_transformer)
+      transformers << custom_transformer
+    end
+
     def <<(field)
       fields[field.name] = field
     end

lib/blueprinter/view_collection.rb

@@ -28,6 +28,10 @@ def fields_for(view_name)
       identifier_fields + sorted_fields
     end
 
+    def transformers(view_name)
+      views[view_name].transformers
+    end
+
     def [](view_name)
       @views[view_name] ||= View.new(view_name)
     end

spec/activerecord_helper.rb

@@ -13,6 +13,10 @@ class Vehicle < ActiveRecord::Base
 class User < ActiveRecord::Base
   attr_accessor :company, :description, :position, :active
   has_many :vehicles
+
+  def dynamic_fields
+    {"full_name" => "#{first_name} #{last_name}"}
+  end
 end
 
 ActiveRecord::Schema.define(version: 20181116094242) do

spec/factories/model_factories.rb

@@ -3,7 +3,7 @@
 FactoryBot.define do
   factory :user do
     first_name { 'Meg' }
-    last_name  { 'Jones' }
+    last_name  { 'Ryan' }
     position { 'Manager' }
     description { 'A person' }
     company { 'Procore' }

spec/integrations/base_spec.rb

@@ -21,7 +21,8 @@
       company: 'Procore',
       birthday: Date.new(1994, 3, 4),
       deleted_at: nil,
-      active: false
+      active: false,
+      dynamic_fields: {"full_name" => "Meg Ryan"}
     }
   end
   let(:object_with_attributes) { OpenStruct.new(obj_hash) }
@@ -288,20 +289,29 @@ def extract(association_name, object, _local_options, _options={})
   end
 
   describe 'Using the ApplicationBlueprint pattern' do
-    let(:obj) { OpenStruct.new(id: 1, name: 'Meg', age: 32) }
+    let(:obj) { OpenStruct.new(id: 1, first_name: 'Meg',last_name:'Ryan', age: 32) }
+    let(:transformer) do
+      Class.new(Blueprinter::Transformer) do
+        def transform(result_hash, object, options={})
+         result_hash.merge!({full_name: "#{object.first_name} #{object.last_name}"})
+        end
+      end
+    end
     let(:application_blueprint) do
+      custom_transformer = transformer
       Class.new(Blueprinter::Base) do
         identifier :id
-        field :name
+        field :first_name
         field(:overridable) { |o| o.name }
 
         view :with_age do
           field :age
+          transform custom_transformer
         end
 
         view :anonymous_age do
           include_view :with_age
-          exclude :name
+          exclude :first_name
         end
       end
     end
@@ -312,38 +322,44 @@ def extract(association_name, object, _local_options, _options={})
 
         view :only_age do
           include_view :with_age
-          exclude :name
+          exclude :first_name
+        end
+
+        view :with_age do
+          field :last_name
         end
       end
     end
 
     subject { blueprint.render_as_hash(obj) }
 
     it('inherits identifier') { expect(subject[:id]).to eq(obj.id) }
-    it('inherits field') { expect(subject[:name]).to eq(obj.name) }
+    it('inherits field') { expect(subject[:first_name]).to eq(obj.first_name) }
     it('overrides field definition') { expect(subject[:overridable]).to eq(obj.age) }
 
     describe 'Inheriting views' do
       let(:view) { :with_age }
       subject { blueprint.render_as_hash(obj, view: view) }
 
       it('includes identifier') { expect(subject[:id]).to eq(obj.id) }
-      it('includes base fields') { expect(subject[:name]).to eq(obj.name) }
+      it('includes base fields') { expect(subject[:first_name]).to eq(obj.first_name) }
       it('includes view fields') { expect(subject[:age]).to eq(obj.age) }
+      it('inherits base fields') { expect(subject[:last_name]).to eq(obj.last_name) }
+      it('inherits transformer fields') { expect(subject[:full_name]).to eq("#{obj.first_name} #{obj.last_name}") }
 
       describe 'With complex views' do
         let(:view) { :anonymous_age }
 
         it('includes identifier') { expect(subject[:id]).to eq(obj.id) }
         it('includes include_view fields') { expect(subject[:age]).to eq(obj.age) }
-        it('excludes excluded fields') { expect(subject).to_not have_key(:name) }
+        it('excludes excluded fields') { expect(subject).to_not have_key(:first_name) }
       end
 
       describe 'Referencing views from parent blueprint' do
         let(:view) { :only_age }
 
         it('includes include_view fields') { expect(subject[:age]).to eq(obj.age) }
-        it('excludes excluded fields') { expect(subject).not_to have_key(:name) }
+        it('excludes excluded fields') { expect(subject).not_to have_key(:first_name) }
       end
     end
   end

spec/integrations/shared/base_render_examples.rb

@@ -425,4 +425,22 @@ def self.unless_method(_field_name, _object, _options)
     end
     it('returns json with values derived from options') { should eq(result) }
   end
+
+  context 'Given blueprint has a transformer' do
+    subject { blueprint.render(obj) }
+    let(:result) { '{"id":' + obj_id + ',"full_name":"Meg Ryan"}' }
+    let(:blueprint) do
+      DynamicFieldsTransformer = Class.new(Blueprinter::Transformer) do
+        def transform(result_hash, object, options={})
+          dynamic_fields = (object.is_a? Hash) ? object[:dynamic_fields] : object.dynamic_fields
+          result_hash.merge!(dynamic_fields)
+        end
+      end
+      Class.new(Blueprinter::Base) do
+        identifier :id
+        transform DynamicFieldsTransformer
+      end
+    end
+    it('returns json with values derived from options') { should eq(result) }
+  end
 end