Making sure destroy/update hooks are added if needed.

lib/thinking_sphinx/active_record.rb

@@ -134,6 +134,11 @@ def define_index(name = nil, &block)
 
         ThinkingSphinx.context.add_indexed_model self
 
+        if sphinx_index_blocks.empty?
+          before_validation :define_indexes
+          before_destroy    :define_indexes
+        end
+
         self.sphinx_index_blocks << lambda {
           index = ThinkingSphinx::Index::Builder.generate self, name, &block
           add_sphinx_callbacks_and_extend(index.delta?)
@@ -311,5 +316,9 @@ def sphinx_document_id
     def sphinx_index_name(suffix)
       "#{self.class.source_of_sphinx_index.name.underscore.tr(':/\\', '_')}_#{suffix}"
     end
+
+    def define_indexes
+      self.class.define_indexes
+    end
   end
 end

spec/thinking_sphinx/active_record_spec.rb

@@ -69,7 +69,33 @@
     end
 
     context 'callbacks' do
-      it "should add a toggle_deleted callback" do
+      it "should add a before_validation callback to define_indexes" do
+        Alpha.should_receive(:before_validation).with(:define_indexes)
+
+        Alpha.define_index { }
+      end
+
+      it "should not add a before_validation callback twice" do
+        Alpha.should_receive(:before_validation).with(:define_indexes).once
+
+        Alpha.define_index { }
+        Alpha.define_index { }
+      end
+
+      it "should add a before_destroy callback to define_indexes" do
+        Alpha.should_receive(:before_destroy).with(:define_indexes)
+
+        Alpha.define_index { }
+      end
+
+      it "should not add a before_destroy callback twice" do
+        Alpha.should_receive(:before_destroy).with(:define_indexes).once
+
+        Alpha.define_index { }
+        Alpha.define_index { }
+      end
+
+      it "should add a toggle_deleted callback when defined" do
         Alpha.should_receive(:after_destroy).with(:toggle_deleted)
 
         Alpha.define_index { indexes :name }
@@ -84,7 +110,7 @@
         Alpha.define_indexes
       end
 
-      it "should add a update_attribute_values callback" do
+      it "should add a update_attribute_values callback when defined" do
         Alpha.should_receive(:after_commit).with(:update_attribute_values)
 
         Alpha.define_index { indexes :name }