Add default value option

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 * Your contribution here.
 
+* [#352](https://github.com/ruby-grape/grape-entity/pull/352): Add Default value option - [@ahmednaguib](https://github.com/ahmednaguib).
+
 #### Fixes
 
 * Your contribution here.

README.md

@@ -24,6 +24,7 @@
       - [Aliases](#aliases)
       - [Format Before Exposing](#format-before-exposing)
       - [Expose Nil](#expose-nil)
+      - [Default Value](#default-value)
       - [Documentation](#documentation)
     - [Options Hash](#options-hash)
       - [Passing Additional Option To Nested Exposure](#passing-additional-option-to-nested-exposure)
@@ -482,6 +483,19 @@ module  Entities
 end
 ```
 
+#### Default Value
+
+This option can be used to provide a default value in case the return value is nil or empty.
+
+```ruby
+module  Entities
+  class MyModel < Grape::Entity
+    expose :name, default: ''
+    expose :age, default: 60
+  end
+end
+```
+
 #### Documentation
 
 Expose documentation with the field. Gets bubbled up when used with Grape and various API documentation systems.

lib/grape_entity/entity.rb

@@ -585,6 +585,7 @@ def to_xml(options = {})
       merge
       expose_nil
       override
+      default
     ].to_set.freeze
 
     # Merges the given options with current block options.

lib/grape_entity/exposure/base.rb

@@ -16,6 +16,7 @@ def initialize(attribute, options, conditions)
           key = options[:as] || attribute
           @key = key.respond_to?(:to_sym) ? key.to_sym : key
           @is_safe = options[:safe]
+          @default_value = options[:default]
           @for_merge = options[:merge]
           @attr_path_proc = options[:attr_path]
           @documentation = options[:documentation]
@@ -82,7 +83,10 @@ def serializable_value(entity, options)
         end
 
         def valid_value(entity, options)
-          value(entity, options) if valid?(entity)
+          return unless valid?(entity)
+
+          output = value(entity, options)
+          output.blank? && @default_value.present? ? @default_value : output
         end
 
         def should_return_key?(options)

spec/grape_entity/entity_spec.rb

@@ -212,6 +212,130 @@ def initialize(a, b, c)
         end
       end
 
+      context 'with :default option' do
+        let(:a) { nil }
+        let(:b) { nil }
+        let(:c) { 'value' }
+
+        context 'when model is a PORO' do
+          let(:model) { Model.new(a, b, c) }
+
+          before do
+            stub_const 'Model', Class.new
+            Model.class_eval do
+              attr_accessor :a, :b, :c
+
+              def initialize(a, b, c)
+                @a = a
+                @b = b
+                @c = c
+              end
+            end
+          end
+
+          context 'when default option is not provided' do
+            it 'exposes attributes values' do
+              subject.expose(:a)
+              subject.expose(:b)
+              subject.expose(:c)
+              expect(subject.represent(model).serializable_hash).to eq(a: nil, b: nil, c: 'value')
+            end
+          end
+
+          context 'when default option is set' do
+            it 'exposes default values for attributes' do
+              subject.expose(:a, default: 'a')
+              subject.expose(:b, default: 'b')
+              subject.expose(:c, default: 'c')
+              expect(subject.represent(model).serializable_hash).to eq(a: 'a', b: 'b', c: 'value')
+            end
+          end
+
+          context 'when default option is set and block passed' do
+            it 'return default value if block returns nil' do
+              subject.expose(:a, default: 'a') do |_obj, _options|
+                nil
+              end
+              subject.expose(:b)
+              subject.expose(:c)
+              expect(subject.represent(model).serializable_hash).to eq(a: 'a', b: nil, c: 'value')
+            end
+
+            it 'return value from block if block returns a value' do
+              subject.expose(:a, default: 'a') do |_obj, _options|
+                100
+              end
+              subject.expose(:b)
+              subject.expose(:c)
+              expect(subject.represent(model).serializable_hash).to eq(a: 100, b: nil, c: 'value')
+            end
+          end
+        end
+
+        context 'when model is a hash' do
+          let(:model) { { a: a, b: b, c: c } }
+
+          context 'when expose_nil option is not provided' do
+            it 'exposes nil attributes' do
+              subject.expose(:a)
+              subject.expose(:b)
+              subject.expose(:c)
+              expect(subject.represent(model).serializable_hash).to eq(a: nil, b: nil, c: 'value')
+            end
+          end
+
+          context 'when expose_nil option is true' do
+            it 'exposes nil attributes' do
+              subject.expose(:a, expose_nil: true)
+              subject.expose(:b, expose_nil: true)
+              subject.expose(:c)
+              expect(subject.represent(model).serializable_hash).to eq(a: nil, b: nil, c: 'value')
+            end
+          end
+
+          context 'when expose_nil option is false' do
+            it 'does not expose nil attributes' do
+              subject.expose(:a, expose_nil: false)
+              subject.expose(:b, expose_nil: false)
+              subject.expose(:c)
+              expect(subject.represent(model).serializable_hash).to eq(c: 'value')
+            end
+
+            it 'is only applied per attribute' do
+              subject.expose(:a, expose_nil: false)
+              subject.expose(:b)
+              subject.expose(:c)
+              expect(subject.represent(model).serializable_hash).to eq(b: nil, c: 'value')
+            end
+
+            it 'raises an error when applied to multiple attribute exposures' do
+              expect { subject.expose(:a, :b, :c, expose_nil: false) }.to raise_error ArgumentError
+            end
+          end
+        end
+
+        context 'with nested structures' do
+          let(:model) { { a: a, b: b, c: { d: nil, e: nil, f: { g: nil, h: nil } } } }
+
+          context 'when expose_nil option is false' do
+            it 'does not expose nil attributes' do
+              subject.expose(:a, expose_nil: false)
+              subject.expose(:b)
+              subject.expose(:c) do
+                subject.expose(:d, expose_nil: false)
+                subject.expose(:e)
+                subject.expose(:f) do
+                  subject.expose(:g, expose_nil: false)
+                  subject.expose(:h)
+                end
+              end
+
+              expect(subject.represent(model).serializable_hash).to eq(b: nil, c: { e: nil, f: { h: nil } })
+            end
+          end
+        end
+      end
+
       context 'with a block' do
         it 'errors out if called with multiple attributes' do
           expect { subject.expose(:name, :email) { true } }.to raise_error ArgumentError