Field definition should remove any existing accessors before setting …

…its own ones

lib/mongoid/fields.rb

@@ -622,6 +622,7 @@ def process_options(field)
       def create_accessors(name, meth, options = {})
         field = fields[name]
 
+        remove_any_existing_accessors(meth)
         create_field_getter(name, meth, field)
         create_field_getter_before_type_cast(name, meth)
         create_field_setter(name, meth, field)
@@ -634,6 +635,19 @@ def create_accessors(name, meth, options = {})
         end
       end
 
+      # Remove any existing accessors that collide with field's ones
+      #
+      # @example Remove any existing accessors.
+      #   Model.remove_any_existing_accessors("name")
+      #
+      # @param [ String ] meth The name of the method.
+      #
+      # @api private
+      def remove_any_existing_accessors(meth)
+        remove_method(meth) if method_defined?(meth, false)
+        remove_method("#{meth}=") if method_defined?("#{meth}=", false)
+      end
+
       # Create the getter method for the provided field.
       #
       # @example Create the getter.

spec/mongoid/fields_spec.rb

@@ -2103,4 +2103,20 @@ class DiscriminatorChild2 < DiscriminatorParent
       end
     end
   end
+
+  context "when accessors are already present" do
+    let(:klass) do
+      Class.new do
+        attr_accessor :name
+        include Mongoid::Document
+        store_in collection: :any
+        field :name
+      end
+    end
+
+    it "they are replaced by the field accessors" do
+      klass.create! name: "Mongoid"
+      expect(klass.find_by.name).to eq("Mongoid")
+    end
+  end
 end