Forbid dynamic fields like in Mongoid

lib/mongo_mapper/plugins/keys.rb

@@ -67,6 +67,22 @@ def load(attrs)
           end.allocate.initialize_from_database(attrs)
         end
 
+        def forbid_dynamic_fields
+          self.allow_dynamic_fields = false
+        end
+
+        def allow_dynamic_fields
+          self.allow_dynamic_fields = true
+        end
+
+        def allow_dynamic_fields=(value)
+          @allow_dynamic_fields = value
+        end
+
+        def allow_dynamic_fields?
+          @allow_dynamic_fields.nil? || @allow_dynamic_fields
+        end
+
         private
           def key_accessors_module_defined?
             if method(:const_defined?).arity == 1 # Ruby 1.9 compat check
@@ -182,10 +198,10 @@ def attributes=(attrs)
         return if attrs == nil or attrs.blank?
 
         attrs.each_pair do |key, value|
-          if respond_to?(:"#{key}=")
-            self.send(:"#{key}=", value)
-          else
+          if !respond_to?(:"#{key}=") and self.class.allow_dynamic_fields?
             self[key] = value
+          else
+            self.send(:"#{key}=", value)
           end
         end
       end

test/unit/test_keys.rb

@@ -86,4 +86,36 @@ def user=(user)
       instance.value.should == nil
     end
   end
+
+  context "forbid dynamic elements" do
+    setup do
+      options = ["self.forbid_dynamic_fields", "self.allow_dynamic_fields = false"]
+      @documents = []
+      options.each do |option|
+        @documents << Class.new do
+          include MongoMapper::Document
+          class_eval option
+          key :valid, String
+        end
+      end
+    end
+
+    should "throw NoMethodError when it wants to initialize non-existent key" do
+      @documents.each do |doc|
+        lambda{ doc.new(:age => 21) }.should raise_error(NoMethodError)
+      end
+    end
+
+    should "throw NoMethodError when it wants to assign value to non-existent key" do
+      @documents.each do |doc|
+        lambda{ doc.new.age = "21" }.should raise_error(NoMethodError)
+      end
+    end
+
+    should "not throw exception when key exists" do
+      @documents.each do |doc|
+        lambda{ doc.new.valid = "Valid" }.should_not raise_error
+      end
+    end
+  end
 end # KeyTest