Okay, I found the solution, there is a way to have fields associated to entities without bundles. You use the same name for bundle as entity. Fortunately, I was also able to use entity reference field. Sharing my experience with everyone -- http://www.innoraft.com/blog/use-entity-reference-your-custom-entities-without-bundles

On Wed, Dec 7, 2011 at 6:56 PM, Mukesh Agarwal <mukesh.agarwal17@gmail.com> wrote:
Hi Guys,

Entities seem to be the biggest problem of my life for the past few weeks :-)

Ok, so I have an entity without any bundles. I read this in hook_entity_info that bundles are not necessary. 

This entry can be omitted if this entity type exposes a single bundle (all entities have the same collection of fields). The name of this single bundle will be the same as the entity type.

Now, I need to attach fields to my entity. I use field_create_field for my entity reference field which seems to work fine. When I attach this field to my instance using field_create_instance, I see an error saying:

drupal FieldException: Attempt to create an instance of field without a bundle

Does this mean I cannot attach fields to entities which do not have bundles? 

--
Cheers,
Mukesh Agarwal
________________________________
Innoraft Solutions  || +91 8017220799




--
Cheers,
Mukesh Agarwal
________________________________
Innoraft Solutions  || +91 8017220799