method

exists?

v4.2.7 - Show latest stable - Class: ActiveRecord::FinderMethods

exists?(conditions = :none)

public

Returns true if a record exists in the table that matches the id or conditions given, or false otherwise. The argument can take six forms:

Integer - Finds the record with this primary key.
String - Finds the record with a primary key corresponding to this string (such as '5').
Array - Finds the record that matches these find-style conditions (such as ['name LIKE ?', "%#{query}%"]).
Hash - Finds the record that matches these find-style conditions (such as {name: 'David'}).
false - Returns always false.
No args - Returns false if the table is empty, true otherwise.

For more information about specifying conditions as a hash or array, see the Conditions section in the introduction to ActiveRecord::Base.

Note: You can’t pass in a condition as a string (like name = 'Jamie'), since it would be sanitized and then queried against the primary key column, like id = 'name = \'Jamie\''.

Person.exists?(5)
Person.exists?('5')
Person.exists?(['name LIKE ?', "%#{query}%"])
Person.exists?(id: [1, 4, 8])
Person.exists?(name: 'David')
Person.exists?(false)
Person.exists?

# File activerecord/lib/active_record/relation/finder_methods.rb, line 277
    def exists?(conditions = :none)
      if Base === conditions
        conditions = conditions.id
        ActiveSupport::Deprecation.warn(          You are passing an instance of ActiveRecord::Base to `exists?`.          Please pass the id of the object by calling `.id`.squish)
      end

      return false if !conditions

      relation = apply_join_dependency(self, construct_join_dependency)
      return false if ActiveRecord::NullRelation === relation

      relation = relation.except(:select, :order).select(ONE_AS_ONE).limit(1)

      case conditions
      when Array, Hash
        relation = relation.where(conditions)
      else
        unless conditions == :none
          relation = relation.where(primary_key => conditions)
        end
      end

      connection.select_value(relation, "#{name} Exists", relation.arel.bind_values + relation.bind_values) ? true : false
    end

1Note

More AREL compliant style is also possible

artemave · Aug 11, 20113 thanks

==== Code example

Person.where(:name => 'David').exists?

exists?

1Note

More AREL compliant style is also possible

Related methods