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module ActiveRecord
module Calculations #:nodoc:
extend ActiveSupport::Concern
CALCULATIONS_OPTIONS = [:conditions, :joins, :order, :select, :group, :having, :distinct, :limit, :offset, :include, :from]
module ClassMethods
# Count operates using three different approaches.
#
# * Count all: By not passing any parameters to count, it will return a count of all the rows for the model.
# * Count using column: By passing a column name to count, it will return a count of all the rows for the model with supplied column present
# * Count using options will find the row count matched by the options used.
#
# The third approach, count using options, accepts an option hash as the only parameter. The options are:
#
# * <tt>:conditions</tt>: An SQL fragment like "administrator = 1" or [ "user_name = ?", username ]. See conditions in the intro to ActiveRecord::Base.
# * <tt>:joins</tt>: Either an SQL fragment for additional joins like "LEFT JOIN comments ON comments.post_id = id" (rarely needed)
# or named associations in the same form used for the <tt>:include</tt> option, which will perform an INNER JOIN on the associated table(s).
# If the value is a string, then the records will be returned read-only since they will have attributes that do not correspond to the table's columns.
# Pass <tt>:readonly => false</tt> to override.
# * <tt>:include</tt>: Named associations that should be loaded alongside using LEFT OUTER JOINs. The symbols named refer
# to already defined associations. When using named associations, count returns the number of DISTINCT items for the model you're counting.
# See eager loading under Associations.
# * <tt>:order</tt>: An SQL fragment like "created_at DESC, name" (really only used with GROUP BY calculations).
# * <tt>:group</tt>: An attribute name by which the result should be grouped. Uses the GROUP BY SQL-clause.
# * <tt>:select</tt>: By default, this is * as in SELECT * FROM, but can be changed if you, for example, want to do a join but not
# include the joined columns.
# * <tt>:distinct</tt>: Set this to true to make this a distinct calculation, such as SELECT COUNT(DISTINCT posts.id) ...
# * <tt>:from</tt> - By default, this is the table name of the class, but can be changed to an alternate table name (or even the name
# of a database view).
#
# 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: <tt>Person.count(:all)</tt> will not work because it will use <tt>:all</tt> as the condition. Use Person.count instead.
def count(*args)
case args.size
when 0
construct_calculation_arel.count
when 1
if args[0].is_a?(Hash)
options = args[0]
distinct = options.has_key?(:distinct) ? options.delete(:distinct) : false
construct_calculation_arel(options).count(options[:select], :distinct => distinct)
else
construct_calculation_arel.count(args[0])
end
when 2
column_name, options = args
distinct = options.has_key?(:distinct) ? options.delete(:distinct) : false
construct_calculation_arel(options).count(column_name, :distinct => distinct)
else
raise ArgumentError, "Unexpected parameters passed to count(): #{args.inspect}"
end
rescue ThrowResult
0
end
# Calculates the average value on a given column. The value is returned as
# a float, or +nil+ if there's no row. See +calculate+ for examples with
# options.
#
# Person.average('age') # => 35.8
def average(column_name, options = {})
calculate(:average, column_name, options)
end
# Calculates the minimum value on a given column. The value is returned
# with the same data type of the column, or +nil+ if there's no row. See
# +calculate+ for examples with options.
#
# Person.minimum('age') # => 7
def minimum(column_name, options = {})
calculate(:minimum, column_name, options)
end
# Calculates the maximum value on a given column. The value is returned
# with the same data type of the column, or +nil+ if there's no row. See
# +calculate+ for examples with options.
#
# Person.maximum('age') # => 93
def maximum(column_name, options = {})
calculate(:maximum, column_name, options)
end
# Calculates the sum of values on a given column. The value is returned
# with the same data type of the column, 0 if there's no row. See
# +calculate+ for examples with options.
#
# Person.sum('age') # => 4562
def sum(column_name, options = {})
calculate(:sum, column_name, options)
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 <tt>:conditions</tt>, <tt>:order</tt>, <tt>:group</tt>, <tt>:having</tt>, and <tt>:joins</tt> 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:
# * <tt>:conditions</tt> - An SQL fragment like "administrator = 1" or [ "user_name = ?", username ]. See conditions in the intro to ActiveRecord::Base.
# * <tt>:include</tt>: Eager loading, see Associations for details. Since calculations don't load anything, the purpose of this is to access fields on joined tables in your conditions, order, or group clauses.
# * <tt>:joins</tt> - An SQL fragment for additional joins like "LEFT JOIN comments ON comments.post_id = id". (Rarely needed).
# The records will be returned read-only since they will have attributes that do not correspond to the table's columns.
# * <tt>:order</tt> - An SQL fragment like "created_at DESC, name" (really only used with GROUP BY calculations).
# * <tt>:group</tt> - An attribute name by which the result should be grouped. Uses the GROUP BY SQL-clause.
# * <tt>:select</tt> - By default, this is * as in SELECT * FROM, but can be changed if you for example want to do a join, but not
# include the joined columns.
# * <tt>:distinct</tt> - Set this to true to make this a distinct calculation, such as SELECT COUNT(DISTINCT posts.id) ...
#
# 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")
def calculate(operation, column_name, options = {})
construct_calculation_arel(options).calculate(operation, column_name, options.slice(:distinct))
rescue ThrowResult
0
end
private
def validate_calculation_options(options = {})
options.assert_valid_keys(CALCULATIONS_OPTIONS)
end
def construct_calculation_arel(options = {})
validate_calculation_options(options)
options = options.except(:distinct)
scope = scope(:find)
includes = merge_includes(scope ? scope[:include] : [], options[:include])
if includes.any?
join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(self, includes, construct_join(options[:joins], scope))
construct_calculation_arel_with_included_associations(options, join_dependency)
else
arel_table.
joins(construct_join(options[:joins], scope)).
from((scope && scope[:from]) || options[:from]).
where(construct_conditions(options[:conditions], scope)).
order(options[:order]).
limit(options[:limit]).
offset(options[:offset]).
group(options[:group]).
having(options[:having]).
select(options[:select] || (scope && scope[:select]) || default_select(options[:joins] || (scope && scope[:joins])))
end
end
def construct_calculation_arel_with_included_associations(options, join_dependency)
scope = scope(:find)
relation = arel_table
for association in join_dependency.join_associations
relation = association.join_relation(relation)
end
relation = relation.joins(construct_join(options[:joins], scope)).
select(column_aliases(join_dependency)).
group(options[:group]).
having(options[:having]).
order(options[:order]).
where(construct_conditions(options[:conditions], scope)).
from((scope && scope[:from]) || options[:from])
relation = relation.where(construct_arel_limited_ids_condition(options, join_dependency)) if !using_limitable_reflections?(join_dependency.reflections) && ((scope && scope[:limit]) || options[:limit])
relation = relation.limit(construct_limit(options[:limit], scope)) if using_limitable_reflections?(join_dependency.reflections)
relation
end
end
end
end
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