Module | ActiveRecord::Calculations::ClassMethods |
In: |
lib/active_record/calculations.rb
|
Calculates average value on a given column. The value is returned as a float. See calculate for examples with options.
Person.average('age')
This calculates aggregate values in the given column: Methods for count, sum, average, minimum, and maximum have been added as shortcuts. Options such as :conditions, :order, :group, :having, and :joins can be passed to customize the query.
There are two basic forms of output:
* Single aggregate value: The single value is type cast to Fixnum for COUNT, Float for AVG, and the given column's type for everything else. * Grouped values: This returns an ordered hash of the values and groups them by the :group option. It takes either a column name, or the name of a belongs_to association. values = Person.maximum(:age, :group => 'last_name') puts values["Drake"] => 43 drake = Family.find_by_last_name('Drake') values = Person.maximum(:age, :group => :family) # Person belongs_to :family puts values[drake] => 43 values.each do |family, max_age| ... end
Options:
Examples:
Person.calculate(:count, :all) # The same as Person.count Person.average(:age) # SELECT AVG(age) FROM people... Person.minimum(:age, :conditions => ['last_name != ?', 'Drake']) # Selects the minimum age for everyone with a last name other than 'Drake' Person.minimum(:age, :having => 'min(age) > 17', :group => :last_name) # Selects the minimum age for any family without any minors
Count operates using three different approaches.
The last approach, count using options, accepts an option hash as the only parameter. The options are:
Examples for counting all:
Person.count # returns the total count of all people
Examples for count by conditions and joins (for backwards compatibility):
Person.count("age > 26") # returns the number of people older than 26 Person.find("age > 26 AND job.salary > 60000", "LEFT JOIN jobs on jobs.person_id = person.id") # returns the total number of rows matching the conditions and joins fetched by SELECT COUNT(*).
Examples for count with options:
Person.count(:conditions => "age > 26") Person.count(:conditions => "age > 26 AND job.salary > 60000", :include => :job) # because of the named association, it finds the DISTINCT count using LEFT OUTER JOIN. Person.count(:conditions => "age > 26 AND job.salary > 60000", :joins => "LEFT JOIN jobs on jobs.person_id = person.id") # finds the number of rows matching the conditions and joins. Person.count('id', :conditions => "age > 26") # Performs a COUNT(id) Person.count(:all, :conditions => "age > 26") # Performs a COUNT(*) (:all is an alias for '*')
Note: Person.count(:all) will not work because it will use :all as the condition. Use Person.count instead.
Calculates the maximum value on a given column. The value is returned with the same data type of the column.. See calculate for examples with options.
Person.maximum('age')
Calculates the minimum value on a given column. The value is returned with the same data type of the column.. See calculate for examples with options.
Person.minimum('age')
Calculates the sum value on a given column. The value is returned with the same data type of the column.. See calculate for examples with options.
Person.sum('age')