Combine two named scopes with OR (instead of AND)

问题:

I want to find all Annotations whose bodies are either:

• Equal to "?"
• or
• Like "[?]"

What's the best way to do this?

I would like to use SearchLogic if possible, but though SearchLogic allows you to do each of the following:

• Annotation.body_equals('?')
• Annotation.body_like('[?]')

and you can always chain them together: Annotation.body_equals('?').body_like('[?]')

I'm not sure how to combine them with OR.

Note that you can combine named scopes with OR if their argument is the same. E.g., I could do:

 Annotation.body_equals_or_body_like('?')

But this wouldn't help.

Note that I'm not attached to SearchLogic, but it would be great for a solution that doesn't require breaking its abstraction.

回答1:

I couldn't find any simple solutions, but this problem intrigued me, so I rolled my own solution:

class ActiveRecord::Base

  def self.or_scopes(*scopes)
    # Cleanup input
    scopes.map! do |scope|
      scope = scope.respond_to?(:to_a) ? scope.to_a : [*scope]
      scope.unshift(scope.shift.to_sym)
    end

    # Check for existence of scopes
    scopes.each{|scope| raise ArgumentError, "invalid scope: #{scope.first}" unless self.scopes.has_key?(scope.first) }

    conditions = scopes.map do |scope|
      scope = self.scopes[scope.first].call(self, *scope[1..-1])
      self.merge_conditions(scope.proxy_options[:conditions])
    end

    or_conditions = conditions.compact.join(" OR ")

    merged_scopes = scopes.inject(self){|merged, scope| merged.scopes[scope.first].call(self, *scope[1..-1]) }

    # We ignore other scope types but so does named_scopes
    find_options = merged_scopes.scope(:find).merge(:conditions => or_conditions)

    self.scoped(find_options)
  end

end

Consider the following setup:

class Person < ActiveRecord::Base
  named_scope :men,      :conditions => { :sex => 'M' }
  named_scope :women,    :conditions => { :sex => 'F' }
  named_scope :children, :conditions => "age < 18"
  named_scope :named, lambda{|name|
    { :conditions => { :name => name } }
  }
end

You call it with the names of a series of scopes as such:

Person.or_scopes(:women, :children)

This returns a scope like this:

Person.or_scopes(:women, :children).proxy_options
# => {:conditions=>"(`people`.`sex` = 'F') OR (age < 18)"}

You can also call it with an array of arrays when the scope requires parameters:

Person.or_scopes(:women, [:named, 'Sue']).proxy_options
# => {:conditions=>"(`people`.`sex` = 'F') OR (`people`.`name` = 'Sue')"}

In your case Horace, you could use the following:

Annotation.or_scopes([:body_equals, '?'], [:body_like, '[?']).all

回答2:

Wouldn't the 'like' results also include the 'equals' results?

You can also use a named scope on the end of another to make a really long named scope. From the Searchlogic Docs (this way seems a bit longwinded to me):

User.username_or_first_name_like("ben")
=> "username LIKE '%ben%' OR first_name like'%ben%'"

User.id_or_age_lt_or_username_or_first_name_begins_with(10)
=> "id < 10 OR age < 10 OR username LIKE 'ben%' OR first_name like'ben%'"

Or you can use a union to combine the search result arrays while removing the duplicates:

@equal_results = Annotation.body_equals('?')
@like_results  = Annotation.body_like('[?]')
@results = @equal_results | @like_results

回答3:

For Rails 2.x, you could use the following named scope to simulate OR:

    __or_fn = lambda do |*scopes|
    where = []
    joins = []
    includes = []

    # for some reason, flatten is actually executing the scope
    scopes = scopes[0] if scopes.size == 1
    scopes.each do |s|
      s = s.proxy_options
      begin
        where << merge_conditions(s[:conditions])
      rescue NoMethodError
        where << scopes[0].first.class.merge_conditions(s[:conditions])
      end
      joins << s[:joins] unless s[:joins].nil?
      includes << s[:include] unless s[:include].nil?
    end
    scoped = self
    scoped = scoped.includes(includes.uniq.flatten) unless includes.blank?
    scoped = scoped.joins(joins.uniq.flatten) unless joins.blank?
    scoped.where(where.join(" OR "))
  end
  named_scope :or, __or_fn

Let's use this function using your example above.

q1 = Annotation.body_equals('?')
q2 = Annotation.body_like('[?]')
Annotation.or(q1,q2)

The above code executes only one query. q1 and q2 do not hold the results of the query, rather, their class is ActiveRecord::NamedScope::Scope.

The or named_scope combines these queries and joins the conditions with an OR.

You could also nest ORs, like in this contrived example:

rabbits = Animal.rabbits
#<Animal id: 1 ...>
puppies = Animal.puppies
#<Animal id: 2 ...>
snakes = Animal.snakes
#<Animal id: 3 ...>
lizards = Animal.lizards
#<Animal id: 4 ...>

Animal.or(rabbits, puppies)
[#<Animal id: 1 ...>, #<Animal id: 2 ...>]
Animal.or(rabbits, puppies, snakes)
[#<Animal id: 1 ...>, #<Animal id: 2 ...>, #<Animal id: 3 ...>]

Because or returns a ActiveRecord::NamedScope::Scope itself, we can go really crazy:

# now let's get crazy
or1 = Animal.or(rabbits, puppies)
or2 = Animal.or(snakes, lizards)
Animal.or(or1, or2)
[#<Animal id: 1 ...>, #<Animal id: 2 ...>, #<Animal id: 3 ...>, #<Animal id: 4...>]

I believe that most of these examples would work fine using scopes in Rails 3, although I have not tried.

A Bit of shameless self-promotion - This functionality is available in the fake_arel gem.

回答4:

I came over this question looking for the answer to "or" two named_scopes and all the answers looked too complex to me. I investigated a bit and found a solution using an additional named_scope called "or" which does the trick.

Following the given example:

Annotation.body_equals('?')
Annotation.body_like('[?]')

both return a named_scope object that construct selects returning annotation records

now we define another named scope expecting two named scopes as parameters like:

named_scope :or, lambda { |l, r| {
  :conditions => 
      "annotations.id IN (#{l.send(:construct_finder_sql,{:select => :id})}) or " + 
      "annotations.id IN (#{r.send(:construct_finder_sql,{:select => :id})})" 
}}

You can then use:

Annotation.or(Annotation.body_equals('?'), Annotation.body_like('[?]'))

This will create a query like:

select * from annotations 
where (annotations.id IN (select id from annotations where body='?') or
      (annotations.id IN (select id from annotations where body like '%?%')

Which is what you were after

As or is also a named_scope, it is possible to chain with other named_scopes including another or:

Annotation.or(Annotation.or(Annotation.body_equals('?'), 
                            Annotation.body_like('[?]')),
              Annotation.some_other)

回答5:

Probably it's

Annotation.body_equals_or_body_like(['?', '[?]'])