Allow arbitrary named_scope instances to be merged

Here's the same patch for 2.1 if anyone wants it.

And again for 2.2.

+1 for the feature - I've definitely run into use cases where I've wanted this, but I'm not sure I agree with the implementation

Also, I could not merge this into 2-3-stable cleanly

I'm not wowed by the implementation - maybe we need a way to chain them ie. Shirt.red.and.dry_clean_only or Shirt.red_and_dry_clean_only

I'll try and post a new patch today. I know that this works with 2.3. I'll have a think about your suggestion.

Here's the patch against 2-3-stable.

Dan, had a think about your suggestion but it doesn't really make sense. It's already possible to do stuff like Shirt.red.dry_clean_only. What I'm asking for is the ability to merge two already-existing scope instances. In my example, you can't just do "z = x.y" because that would be treating y as a method name, not a local variable name.

@james, Not clear what you are after.

You can chain named_scopes for a while now, but you want AND on the return record set ?

@Elad, I think he's looking for the union of two named scopes. So if we had a named scope to return all green M&M's and a named scope to return all red M&M's, he'd want to be able to quickly get the collection of M&M's that are either red or green (the union of the two sets).

I'm not sure I'd use the term "union" because conditions in one scope might remove records included by the other scope. I just want to merge two scopes together, like you do with chaining (it would give the same result), but for scopes that have already been assigned to variables. It's difficult to give a useful example.

The name doesn't make a whole lot of sense - I was really hoping you'd written an implementation of scope union (joining with OR) rather than this.

This is also going (I think) to fail oddly if you try to merge in a previously chained scope:

x = Shirt.red.cotton
y = Shirt.dry_clean_only

z = y.merge(x)

Because of that, I'm not sure what the advantage of merge over just chaining the scopes properly in the first place is.

Note that the most common case for this (search scopes and such) can work like this:

proxy = Shirt
[:red, :cotton, :dry_clean_only].each do |s|
  proxy = proxy.send(s) unless params[s].blank?
end
@shirts = proxy.all # or paginate - whatever

Maybe you could give a more convincing use case where chaining doesn't work?

verified

Patch applies cleanly to 2-3-stable. I assume the tests are passing, I'm having some problems getting Ruby 1.9 and 1.8 play nicely. +1 on the idea, it may need more tests, though.

I agree with Matt, i don't see where this #merge is going to be any different from chaining scopes.

That's fair enough. Thanks for the info.