Allow identifiers to be defined with a block

Now that `::association` and `::field` receive an optional block,
`::identifier` should receive it as well.

Since all three methods receive an optional block, the block extraction
mechanism was moved to `AutoExtractor`. Removing this mechanism from
each individual method made them very similar. `::association` now uses
`::field` instead of directly adding the field to the current view.

README.md

@@ -186,6 +186,32 @@ Output:
 }
 ```
 
+#### Defining an identifier directly in the Blueprint
+
+You can also pass a block to an identifier:
+
+```ruby
+class UserBlueprint < Blueprinter::Base
+  identifier :uuid do |user, options|
+    options[:current_user].anonymize(user.uuid)
+  end
+end
+```
+
+Usage:
+
+```ruby
+puts UserBlueprint.render(user, current_user: current_user)
+```
+
+Output:
+
+```json
+{
+  "uuid": "733f0758-8f21-4719-875f-262c3ec743af",
+}
+```
+
 #### Defining an association directly in the Blueprint
 
 You can also pass a block to an association:

lib/blueprinter/base.rb

@@ -26,6 +26,9 @@ class Base
     # @param name [Symbol] to rename the identifier key in the JSON
     #   output. Defaults to method given.
     # @param extractor [AssociationExtractor,AutoExtractor,BlockExtractor,HashExtractor,PublicSendExtractor]
+    # @yield [object, options] The object and the options passed to render are
+    #   also yielded to the block.
+    #
     #   Kind of extractor to use.
     #   Either define your own or use Blueprinter's premade extractors.
     #   Defaults to AutoExtractor
@@ -36,13 +39,22 @@ class Base
     #     # other code
     #   end
     #
+    # @example Passing a block to be evaluated as the value.
+    #   class UserBlueprint < Blueprinter::Base
+    #     identifier :uuid do |user, options|
+    #       options[:current_user].anonymize(user.uuid)
+    #     end
+    #   end
+    #
     # @return [Field] A Field object
-    def self.identifier(method, name: method, extractor: AutoExtractor.new)
-      view_collection[:identifier] << Field.new(method, name, extractor, self)
-    end
-
-    def self.inherited(subclass)
-      subclass.send(:view_collection).inherit(view_collection)
+    def self.identifier(method, name: method, extractor: AutoExtractor.new, &block)
+      view_collection[:identifier] << Field.new(
+        method,
+        name,
+        extractor,
+        self,
+        block: block,
+      )
     end
 
     # Specify a field or method name to be included for serialization.
@@ -98,16 +110,13 @@ def self.inherited(subclass)
     #
     # @return [Field] A Field object
     def self.field(method, options = {}, &block)
-      options = if block_given?
-        {name: method, extractor: BlockExtractor.new, block: block}
-      else
-        {name: method, extractor: AutoExtractor.new}
-      end.merge(options)
-      current_view << Field.new(method,
-                                options[:name],
-                                options[:extractor],
-                                self,
-                                options)
+      current_view << Field.new(
+        method,
+        options.fetch(:name) { method },
+        options.fetch(:extractor) { AutoExtractor.new },
+        self,
+        options.merge(block: block),
+      )
     end
 
     # Specify an associated object to be included for serialization.
@@ -141,19 +150,12 @@ def self.field(method, options = {}, &block)
     # @return [Field] A Field object
     def self.association(method, options = {}, &block)
       raise BlueprinterError, 'blueprint required' unless options[:blueprint]
-      name = options.delete(:name) || method
-
-      options = if block_given?
-        options.merge(extractor: BlockExtractor.new, block: block)
-      else
-        options.merge(extractor: AutoExtractor.new)
-      end
 
-      current_view << Field.new(method,
-                                name,
-                                AssociationExtractor.new,
-                                self,
-                                options.merge(association: true))
+      field(
+        method,
+        options.merge(association: true, extractor: AssociationExtractor.new),
+        &block
+      )
     end
 
     # Generates a JSON formatted String.
@@ -313,6 +315,11 @@ def self.view(view_name)
 
     private
 
+    def self.inherited(subclass)
+      subclass.send(:view_collection).inherit(view_collection)
+    end
+    private_class_method :inherited
+
     def self.object_to_hash(object, view_name:, local_options:)
       view_collection.fields_for(view_name).each_with_object({}) do |field, hash|
         next if field.skip?(object, local_options)

lib/blueprinter/extractors/association_extractor.rb

@@ -1,7 +1,11 @@
 module Blueprinter
   class AssociationExtractor < Extractor
+    def initialize
+      @extractor = AutoExtractor.new
+    end
+
     def extract(association_name, object, local_options, options={})
-      value = options[:extractor].extract(association_name, object, local_options, options)
+      value = @extractor.extract(association_name, object, local_options, options)
       return options[:default] if value.nil?
       view = options[:view] || :default
       options[:blueprint].prepare(value, view_name: view, local_options: local_options)

lib/blueprinter/extractors/auto_extractor.rb

@@ -3,16 +3,26 @@ class AutoExtractor < Extractor
     def initialize
       @hash_extractor = HashExtractor.new
       @public_send_extractor = PublicSendExtractor.new
+      @block_extractor = BlockExtractor.new
     end
 
     def extract(field_name, object, local_options, options = {})
-      extractor = object.is_a?(Hash) ? @hash_extractor : @public_send_extractor
-      extraction = extractor.extract(field_name, object, local_options, options)
+      extraction = extractor(object, options).extract(field_name, object, local_options, options)
       options.key?(:datetime_format) ? format_datetime(extraction, options[:datetime_format]) : extraction
     end
 
     private
 
+    def extractor(object, options)
+      if options[:block]
+        @block_extractor
+      elsif object.is_a?(Hash)
+        @hash_extractor
+      else
+        @public_send_extractor
+      end
+    end
+
     def format_datetime(datetime, format)
       datetime.strftime(format)
     rescue NoMethodError

spec/integrations/base_spec.rb

@@ -158,6 +158,34 @@
     end
   end
 
+  describe 'identifier' do
+    let(:rendered) do
+      blueprint.render_as_hash(OpenStruct.new(uid: 42))
+    end
+
+    let(:blueprint) do
+      Class.new(Blueprinter::Base) do
+        identifier :uid
+      end
+    end
+
+    it "renders identifier" do
+      expect(rendered).to eq(uid: 42)
+    end
+
+    describe 'Given a block is passed' do
+      let(:blueprint) do
+        Class.new(Blueprinter::Base) do
+          identifier(:id) { |object, _| object.uid * 2 }
+        end
+      end
+
+      it "renders result of block" do
+        expect(rendered).to eq(id: 84)
+      end
+    end
+  end
+
   describe 'Using the ApplicationBlueprint pattern' do
     let(:obj) { OpenStruct.new(id: 1, name: 'Meg', age: 32) }
     let(:application_blueprint) do