I'm new to the new query interface of ActiveRecord so I'm still figuring things out.
I was hoping someone could explain the difference between using a scope
in an ActiveRecord model and just using a class method (ie self.some_method
)
From what I can gather, a scope is always expected to return a relation, whereas a class method doesn't necessarily have to. Is this true?
For instance, I thought it would make sense to do something like:
class Person
scope :grouped_counts, group(:name).count
end
But this doesn't work. I get this error:
ArgumentError: Unknown key(s): communicating, failed, matched, unmatched
from /Users/bradrobertson/.rvm/gems/ruby-1.9.2-p180@influitive/gems/activesupport-3.0.5/lib/active_support/core_ext/hash/keys.rb:43:in `assert_valid_keys'
from /Users/bradrobertson/.rvm/gems/ruby-1.9.2-p180@influitive/gems/activerecord-3.0.5/lib/active_record/relation/spawn_methods.rb:110:in `apply_finder_options'
from /Users/bradrobertson/.rvm/gems/ruby-1.9.2-p180@influitive/gems/activerecord-3.0.5/lib/active_record/named_scope.rb:110:in `block in scope'
from (irb):48
from /Users/bradrobertson/.rvm/gems/ruby-1.9.2-p180@influitive/gems/railties-3.0.5/lib/rails/commands/console.rb:44:in `start'
from /Users/bradrobertson/.rvm/gems/ruby-1.9.2-p180@influitive/gems/railties-3.0.5/lib/rails/commands/console.rb:8:in `start'
from /Users/bradrobertson/.rvm/gems/ruby-1.9.2-p180@influitive/gems/railties-3.0.5/lib/rails/commands.rb:23:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
r
It does however work as a class method
def self.grouped_counts
group(:name).count
end
I'm interested to know peoples' thoughts on when to use scopes and when to use class methods. Am I correct in assuming that a scope must always return a relation, but a class method can return whatever it wants?