Chain scopes with OR

rubyonrails-talk
1

Hi all!

I’ve googled all over and I couldn’t find anything about chaining scopes with OR instead of the default AND.

I have an Asset model with the following scopes:

class Asset < ActiveRecord::Base

(…)

scope :find_in_coverage, lambda { where(‘timestamp(assets.found_at) >= ?’, Asset.found_at_limit) }

scope :find_unknown_in_coverage, where(‘assets.asset_type_id IS NULL’).find_in_coverage

scope :find_known_missing, lambda { where(‘assets.found_at < ? AND assets.asset_type_id IS NOT NULL’, Asset.found_at_limit) }

end

I would like to create another scope (“find_visibles”) which is the OR of “find_in_coverage” and “find_known_missing” scopes, like that:

scope :find_visibles, find_in_coverage.find_know_missing

The problem is that this method chain uses AND to concatenate WHERE clauses. I need this clauses to be concatenated using OR instead.

How can I do that?

Thanks in advance,

Gustavo Honorato

2

AFAIK, something like this should work:

def find_visibles

find_in_coverage | find_known_missing

end

3

To add to that, if you want to construct complex queries, you should have a look at arel.

4

The problem of the first solution is that “find_in_coverage | find_known_missing” combined that way does not return a scope. It returns two arrays each and applies | operator on the result. See: http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-7C

I’ve looked arel docs (in fact, I just found poor docs). Can you please point me where in docs is explaining how I can construct such query?

Thanks for you attention,

Gustavo

5

The problem of the first solution is that “find_in_coverage | find_known_missing” combined that way does not return a scope. It returns two arrays each and applies | operator on the result. See: http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-7C

I’ve looked arel docs (in fact, I just found poor docs). Can you please point me where in docs is explaining how I can construct such query?

Have you read the README for arel? (https://github.com/rails/arel)

"The OR operator works like this:

users.where(users[:name].eq(‘bob’).or(users[:age].lt(25)))"

I don’t think you can do this through scopes, so working arel is the best alternative, but it may just be more hassle than you need. If you want a really hacky solution, I’ve done stuff like this in the past:

recipe_query = Recipe.where(“pastry_id = 1”).where(“filling_id = 1”)

Recipe.where(recipe_query.where_values.join(" OR "))

That generates:

SELECT “recipes”.* FROM “recipes” WHERE (pastry_id = 1 OR filling_id = 1)

That might give you some ideas. It goes without saying that this is some hacky stuff you’re getting into, so I’d tread carefully!

Jeremy Walker

http://www.ihid.co.uk

6

try

escopo: find_visibles, lambda { find_in_coverage.find_know_missing}

7

@Rogerio: This way the scopes are merged with AND not OR

@Jeremy: I’ve read README and I haven’t found a way to join scopes with OR, as you mentioned. The only way I found is to join attributes with OR, not scopes. I’ve tried that hack (where_clauses.join(‘OR’)) before too. The problem is that, for some reason, it don’t work when we use the scope chained with a association.

I’ve googled a lot and I found a lot of people complaining about this missing feature. I’m a big fan of Rails, but it is a pitty that Rails doesn’t give any simple way to do that. I really want to avoid that, but the best solution that I can see is to duplicate the code of the first two scopes on find_visibles.

Thanks,

Gustavo

8

Hi Gustavo

Coincidentally, I was recently doing something similar. Older versions of rails used to evaluate my previous solution using " | " to an ActiveRelation. When this stopped I dont know, or maybe I am just mistaken. In any case, I finally settled on using the squeel gem, the arel docs, I agree are quite horrible.

There are examples on ‘OR’ queries with squeel on the github readme.

9

U try ?

escopo: find_visibles, lambda { find_in_coverage|find_know_

missing}