Added missing id setter

lib/active_fedora/core.rb

@@ -138,7 +138,7 @@ def id_to_uri(id)
         else
           id = "/#{id}" unless id.start_with? SLASH
           unless ActiveFedora.fedora.base_path == SLASH || id.start_with?("#{ActiveFedora.fedora.base_path}/")
-            id = ActiveFedora.fedora.base_path + id 
+            id = ActiveFedora.fedora.base_path + id
           end
           ActiveFedora.fedora.host + id
         end

lib/active_fedora/fedora_attributes.rb

@@ -34,6 +34,12 @@ def id
       end
     end
 
+    def id=(id)
+      raise "ID has already been set to #{self.id}" if self.id
+      @ldp_source = build_ldp_resource(id.to_s)
+    end
+
+
     # TODO: Remove after we no longer support #pid.
     def pid
       Deprecation.warn FedoraAttributes, "#{self.class}#pid is deprecated and will be removed in active-fedora 10.0. Use #{self.class}#id instead."

spec/unit/base_spec.rb

@@ -4,6 +4,30 @@
 describe ActiveFedora::Base do
   it_behaves_like "An ActiveModel"
 
+  describe "id=" do
+    before do
+      class FooHistory < ActiveFedora::Base
+        property :title, predicate: ::RDF::DC.title
+      end
+    end
+    after do
+      Object.send(:remove_const, :FooHistory)
+    end
+
+    subject { FooHistory.new(title: ["A good title"]) }
+    before { subject.id = 9 }
+
+    it "is settable" do
+      expect(subject.id).to eq '9'
+      expect(subject.title).to eq ["A good title"]
+    end
+
+    it "is only settable once" do
+      expect { subject.id = 10 }.to raise_error "ID has already been set to 9"
+      expect(subject.id).to eq '9'
+    end
+  end
+
   describe 'descendants' do
     it "should record the decendants" do
       expect(ActiveFedora::Base.descendants).to include(ModsArticle, SpecialThing)