HABTM vs. using has_many :through

Rails
1

All,

I’ve heard recently about has_many :through as a necessary alternative
to HABTM (when the join table has it’s own id column, say, in a legacy
schema). However, is the prevailing Rails wisdom now that one should
use has_many :through in all cases?

If so, why?

Thanks,
Wes

2

Uber associationatire Josh S. has written a much recommended article
outlining the features and pros/cons of habtm and hmt:
http://blog.hasmanythrough.com/articles/2006/04/20/many-to-many-dance-off.

However, is the prevailing Rails wisdom now that one should
use has_many :through in all cases?
As with a lot of Rails wisdom the short answer is ‘it depends’ :0)

Steve

3

It may be heresy to some, but I still prefer HABTM over
has_many :through if the relationship I’m dealing with is simple.
i.e., if there’s no reason to store any metainfo in a join model, I
just use HABTM. I like my proxy collections!

This doesn’t mean I don’t love (and use) has_many :through for
situations when there does need to be metainfo stored about the
relationship. But I always ask myself first before I decide which to
use.

-Seth

4

Agreed.

5

Wes G. wrote:

All,

I’ve heard recently about has_many :through as a necessary alternative
to HABTM (when the join table has it’s own id column, say, in a legacy
schema). However, is the prevailing Rails wisdom now that one should
use has_many :through in all cases?

Not at all.

Think about the model first. Do you want to model your associations
explicitly, using a model class? In other words, are there things that
you want to say about the associations? (Can you put a name to them?
This may help you to find things that you might want to say about them.)
If so, use a model for the association… and then you will need the
:through capability to let you navigate through the association in a
single query.

If you just want the association to exist, with nothing further being
said about it, stick with HABTM.

In other words, I agree with others in this thread, but would like to
put the emphasis on thinking carefully about the domain model.

regards

Justin