none query method

[xuanxu]

Here is a none method to return an empty relation from a AR model (i.e Post.none), as previously discussed here: #4548

It prevents the query hitting the database, is chainable and makes any subsequent relation empty, so Post.none.where(:author_id => 1) is also empty.

[Empact]

You might want to just update the code in the original pull request, to keep the conversation together there.

BTW I'm +1 on this idea. .where('1 = 0') is a lame hack.

[tenderlove]

I'm OK with this, but I'd like more opinions. @jonleighton ?

[jonleighton]

I'm okay with this too, but I think it would be better if:

• The rationale was explained in the documentation (also explained in terms of the 'null object pattern' as that's what this is)
• There was a CHANGELOG entry
• Ideally I'd prefer if we used polymorphism. I.e. if Relation#none returned an instance of a NullRelation that implemented this behaviour, rather than having to have a @none_value var and special code in exec_queries.

Thanks.

[tenderlove]

I agree with @jonleighton. @xuanxu can you make those changes, and we'll merge it in. Thanks for the contribution! :-)

[xuanxu]

OK, I will try to make those changes

[xuanxu]

@tenderlove Done!: #4768
¿should I backport it to 3.2?

[tenderlove]

@jonleighton can you review?

@xuanxu no, we will not backport this (as it is a new feature).