Module | ActiveRecord::Calculations::ClassMethods |
In: |
vendor/rails/activerecord/lib/active_record/calculations.rb
|
Calculates the average value on a given column. The value is returned as a float. See calculate for examples with options.
Person.average('age')
# File vendor/rails/activerecord/lib/active_record/calculations.rb, line 52 52: def average(column_name, options = {}) 53: calculate(:avg, column_name, options) 54: end
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 <tt>:group</tt> 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 Person.sum("2 * age")
# File vendor/rails/activerecord/lib/active_record/calculations.rb, line 115 115: def calculate(operation, column_name, options = {}) 116: validate_calculation_options(operation, options) 117: column_name = options[:select] if options[:select] 118: column_name = '*' if column_name == :all 119: column = column_for column_name 120: catch :invalid_query do 121: if options[:group] 122: return execute_grouped_calculation(operation, column_name, column, options) 123: else 124: return execute_simple_calculation(operation, column_name, column, options) 125: end 126: end 127: 0 128: end
Count operates using three different approaches.
The third 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 counting by column:
Person.count(:age) # returns the total count of all people whose age is present in database
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.
# File vendor/rails/activerecord/lib/active_record/calculations.rb, line 45 45: def count(*args) 46: calculate(:count, *construct_count_options_from_args(*args)) 47: end
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')
# File vendor/rails/activerecord/lib/active_record/calculations.rb, line 66 66: def maximum(column_name, options = {}) 67: calculate(:max, column_name, options) 68: end
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')
# File vendor/rails/activerecord/lib/active_record/calculations.rb, line 59 59: def minimum(column_name, options = {}) 60: calculate(:min, column_name, options) 61: end
Calculates the sum of values 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')
# File vendor/rails/activerecord/lib/active_record/calculations.rb, line 73 73: def sum(column_name, options = {}) 74: calculate(:sum, column_name, options) || 0 75: end
# File vendor/rails/activerecord/lib/active_record/calculations.rb, line 131 131: def construct_count_options_from_args(*args) 132: options = {} 133: column_name = :all 134: 135: # We need to handle 136: # count() 137: # count(:column_name=:all) 138: # count(options={}) 139: # count(column_name=:all, options={}) 140: case args.size 141: when 1 142: args[0].is_a?(Hash) ? options = args[0] : column_name = args[0] 143: when 2 144: column_name, options = args 145: else 146: raise ArgumentError, "Unexpected parameters passed to count(): #{args.inspect}" 147: end if args.size > 0 148: 149: [column_name, options] 150: end