Question

Does anyone know how to go about designing tag system similar to the one used here, at stackoverflow?

Any links that would explain on how to go about implementing this system with hibernate/spring would be awesome.

I’m just looking for some starting point.

Answer 1

I would suggest starting with three Entities, one for the object that is being tagged (is in the case of the SO example, this would be a Post), one for holding your tag definitions (you can just call this Tag), and one for mapping between the two (call this one TaggedPost).

Then the basic process of assigning a Tag to a Post goes something like:

1. See if a Tag with the given name already exists, if yes, use the existing one, otherwise insert a new one.
2. Create a new TaggedPost instance that links the Post with the Tag from step 1.

To remove a Tag from a Post you just delete the corresponding TaggedPost entity.

You can use Hibernate annotations to expose the set of tags that are applied to a given Post as a Java Collection so that you can just say getTags() to get all the tags. And you can do the same thing on Tag so that you can say getPosts() to get all the posts that have a given Tag.