v2.0.3 - Show latest stable - 4 notes - Class: ActiveRecord::Base
exists?(id_or_conditions) public

Checks whether a record exists in the database that matches conditions given. These conditions can either be a single integer representing a primary key id to be found, or a condition to be matched like using ActiveRecord#find.

The id_or_conditions parameter can be an Integer or a String if you want to search the primary key column of the table for a matching id, or if you’re looking to match against a condition you can use an Array or a Hash.

Possible gotcha: You can’t pass in a condition as a string e.g. "name = ‘Jamie’", this would be sanitized and then queried against the primary key column as "id = ‘name = \’Jamie"


  Person.exists?(:name => "David")
  Person.exists?(['name LIKE ?', "%#{query}%"])
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February 3, 2009
3 thanks

Possible gotcha

Please note that exists? doesn’t hold all the conventions of find, i.e. you can’t do:

Person.exists?(:conditions => ['name LIKE ?', "%#{query}%"]) # DOESN'T WORK!
January 30, 2009 - (<= v2.1.0)
3 thanks

Hash conditions require explicit key and value

When condition passed as hash, the behavior is different from a finder method. Finder methods, such as:

find(:all, :user=>user)

will apply the user_id = convention, provided user is an association (e.g. belongs_to :user). The exists? method will not do the same. You must specify the foreign key name and value explicitly, i.e:

September 9, 2010
2 thanks

takes ActiveRecord object as an arg as well

One undocumented feature, you can do this:

person = Person.first
# => returns true

This came in handy for me when I needed to see if something belonged to a particular scope.

scope = "created_rails"
person = Person.find_by_name "dhh"
# => returns true

Obviously this relies on you having a named_scope in your Person model called “created_rails”.

April 22, 2010
2 thanks

Dynamic exists? methods

There are no dynamic exists? methods analogous to dynamic finders, which means that while you can do this:


you can’t do this:

Person.exists_by_name('David') # DOES NOT WORK

nor this:

Person.exists_by_name?('David') # DOES NOT WORK

However, you can simulate this with dynamic scope:


You’ll have to admit that this is so much better than the plain old method:

Person.exists?(:name => "David")