executing named_scoped only when there are present params

Question

Hi have a model like this:

class EventDate < ActiveRecord::Base
belongs_to :event

named_scope :named, lambda { | name | { 
    :joins => { :event => :core}, 
    :conditions => ["name like ?", "%#{ name }%"] 
  }}

  named_scope :date_range, lambda { | start, length | { 
    :conditions => ["day >= ? AND day <= ?", start, date + (length || 30) ]
  }}

it works correctly if i launch name = "ba" start = Date.today EventDate.named(name).date_range(start , start + 2)

But if the name or the start is nil i don't want execute the named_scope like name = nil EventDate.named(name).date_range(start , start + 2)

Is possible to set a condition inner the named_scope ?

thanks

Answer 1

Yes, just do:

unless name.blank?

Inside the lambda. In this way you can also set a default query to execute if the param is not given

Answer 2

Named_scope was not intended to handle that kind of logic. It was built to help you set certain conditions that might arise often.

The caller should call appropriate named_scope depending on params available, i.e. just add a condition before calling named_scope. For example:

if name.blank?
  EventDate.date_range(start, end)
else
  EventDate.named(name).date_range(start, end)
end

That being said, technically you could do something similar within a scope itself. Lambda created for the named_scope needs to return a hash and you could put your check in it (but please don't do this!) and return empty hash if name is empty. For example:

named_scope :named, lambda { | name |
  name.blank? ? {} : { :conditions => ["name like ?", "%#{ name }%"] }
}