Mongoid now raises an error when defining a field with a conflicting …

…name on a document (Github: 69)

lib/mongoid/config.rb

@@ -85,6 +85,25 @@ def slaves
       @slaves
     end
 
+    # Return field names that could cause destructive things to happen if
+    # defined in a Mongoid::Document
+    #
+    # Example:
+    #
+    # <tt>Config.destructive_fields</tt>
+    #
+    # Returns:
+    #
+    # An array of bad field names.
+    def destructive_fields
+      @destructive_fields ||= lambda {
+        klass = Class.new do
+          include Mongoid::Document
+        end
+        klass.instance_methods(true)
+      }.call
+    end
+
     protected
     def check_database!(database)
       raise Errors::InvalidDatabase.new(database) unless database.kind_of?(Mongo::DB)

lib/mongoid/errors.rb

@@ -87,5 +87,22 @@ def message
       end
     end
 
+    # This error is raised when trying to create a field that conflicts with
+    # a Mongoid internal attribute or method.
+    #
+    # Example:
+    #
+    # <tt>InvalidField.new('collection')</tt>
+    class InvalidField < RuntimeError
+      def initialize(name)
+        @name = name
+      end
+      def message
+        "Defining a field named '#{@name}' is not allowed. " +
+          "Do not define fields that conflict with Mongoid internal attributes " +
+          "or method names. Use Document#instance_methods to see what " +
+          "names this includes."
+      end
+    end
   end
 end

lib/mongoid/field.rb

@@ -33,6 +33,7 @@ def default
     #
     # <tt>Field.new(:score, :default => 0)</tt>
     def initialize(name, options = {})
+      check_name!(name)
       @name, @default = name, options[:default]
       @copyable = (@default.is_a?(Array) || @default.is_a?(Hash))
       @type = options[:type] || String
@@ -55,5 +56,10 @@ def get(object)
     def copy
       @copyable ? @default.dup : @default
     end
+
+    # Check if the name is valid.
+    def check_name!(name)
+      raise Errors::InvalidField.new(name) if Mongoid.destructive_fields.include?(name.to_s)
+    end
   end
 end

spec/unit/mongoid/config_spec.rb

@@ -19,6 +19,13 @@
     end
   end
 
+  describe "#destructive_fields" do
+
+    it "returns an array of bad field names" do
+      config.destructive_fields.should include("collection")
+    end
+  end
+
   describe "#master=" do
 
     context "when object provided is not a Mongo::DB" do

spec/unit/mongoid/errors_spec.rb

@@ -101,4 +101,21 @@
       end
     end
   end
+
+  describe Mongoid::Errors::InvalidField do
+
+    describe "#message" do
+
+      context "default" do
+
+        before do
+          @error = Mongoid::Errors::InvalidField.new("collection")
+        end
+
+        it "contains class is not allowed" do
+          @error.message.should include("field named 'collection' is not allowed")
+        end
+      end
+    end
+  end
 end

spec/unit/mongoid/field_spec.rb

@@ -76,6 +76,16 @@
 
   end
 
+  describe "#initialize" do
+
+    context "when the field name is invalid" do
+
+      it "raises an error" do
+        lambda { Mongoid::Field.new(:collection) }.should raise_error(Mongoid::Errors::InvalidField)
+      end
+    end
+  end
+
   describe "#name" do
 
     before do