module ActiveRecord
module Calculations #:nodoc:
CALCULATIONS_OPTIONS = [:conditions, :joins, :order, :select, :group, :having, :distinct, :limit, :offset]
def self.included(base)
base.extend(ClassMethods)
end
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 by conditions or joins: For backwards compatibility, you can pass in +conditions+ and +joins+ as individual parameters.
# * Count using options will find the row count matched by the options used.
#
# The last 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.
# * <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>: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 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) ...
#
# 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.
def count(*args)
options = {}
column_name = :all
# For backwards compatibility, we need to handle both count(conditions=nil, joins=nil) or count(options={}) or count(column_name=:all, options={}).
if args.size >= 0 && args.size <= 2
if args.first.is_a?(Hash)
options = args.first
elsif args[1].is_a?(Hash)
options = args[1]
column_name = args.first
else
# Handle legacy paramter options: def count(conditions=nil, joins=nil)
options.merge!(:conditions => args[0]) if args.length > 0
options.merge!(:joins => args[1]) if args.length > 1
end
else
raise(ArgumentError, "Unexpected parameters passed to count(*args): expected either count(conditions=nil, joins=nil) or count(options={})")
end
if options[:include] || scope(:find, :include)
count_with_associations(options)
else
calculate(:count, column_name, options)
end
end
# Calculates average value on a given column. The value is returned as a float. See #calculate for examples with options.
#
# Person.average('age')
def average(column_name, options = {})
calculate(:avg, column_name, options)
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')
def minimum(column_name, options = {})
calculate(:min, column_name, options)
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')
def maximum(column_name, options = {})
calculate(:max, column_name, options)
end
# 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')
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 :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:
# * <tt>:conditions</tt>: An SQL fragment like "administrator = 1" or [ "user_name = ?", username ]. See conditions in the intro.
# * <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
def calculate(operation, column_name, options = {})
validate_calculation_options(operation, options)
column_name = options[:select] if options[:select]
column_name = '*' if column_name == :all
column = column_for column_name
aggregate = select_aggregate(operation, column_name, options)
aggregate_alias = column_alias_for(operation, column_name)
if options[:group]
execute_grouped_calculation(operation, column_name, column, aggregate, aggregate_alias, options)
else
execute_simple_calculation(operation, column_name, column, aggregate, aggregate_alias, options)
end
end
protected
def construct_calculation_sql(aggregate, aggregate_alias, options) #:nodoc:
scope = scope(:find)
sql = "SELECT #{aggregate} AS #{aggregate_alias}"
sql << ", #{options[:group_field]} AS #{options[:group_alias]}" if options[:group]
sql << " FROM #{table_name} "
add_joins!(sql, options, scope)
add_conditions!(sql, options[:conditions], scope)
sql << " GROUP BY #{options[:group_field]}" if options[:group]
sql << " HAVING #{options[:having]}" if options[:group] && options[:having]
sql << " ORDER BY #{options[:order]}" if options[:order]
add_limit!(sql, options)
sql
end
def execute_simple_calculation(operation, column_name, column, aggregate, aggregate_alias, options) #:nodoc:
value = connection.select_value(construct_calculation_sql(aggregate, aggregate_alias, options))
type_cast_calculated_value(value, column, operation)
end
def execute_grouped_calculation(operation, column_name, column, aggregate, aggregate_alias, options) #:nodoc:
group_attr = options[:group].to_s
association = reflect_on_association(group_attr.to_sym)
associated = association && association.macro == :belongs_to # only count belongs_to associations
group_field = (associated ? "#{options[:group]}_id" : options[:group]).to_s
group_alias = column_alias_for(group_field)
group_column = column_for group_field
sql = construct_calculation_sql(aggregate, aggregate_alias, options.merge(:group_field => group_field, :group_alias => group_alias))
calculated_data = connection.select_all(sql)
if association
key_ids = calculated_data.collect { |row| row[group_alias] }
key_records = association.klass.base_class.find(key_ids)
key_records = key_records.inject({}) { |hsh, r| hsh.merge(r.id => r) }
end
calculated_data.inject(OrderedHash.new) do |all, row|
key = associated ? key_records[row[group_alias].to_i] : type_cast_calculated_value(row[group_alias], group_column)
value = row[aggregate_alias]
all << [key, type_cast_calculated_value(value, column, operation)]
end
end
private
def validate_calculation_options(operation, options = {})
if operation.to_s == 'count'
options.assert_valid_keys(CALCULATIONS_OPTIONS + [:include])
else
options.assert_valid_keys(CALCULATIONS_OPTIONS)
end
end
def select_aggregate(operation, column_name, options)
"#{operation}(#{'DISTINCT ' if options[:distinct]}#{column_name})"
end
# converts a given key to the value that the database adapter returns as
#
# users.id #=> users_id
# sum(id) #=> sum_id
# count(distinct users.id) #=> count_distinct_users_id
# count(*) #=> count_all
def column_alias_for(*keys)
keys.join(' ').downcase.gsub(/\*/, 'all').gsub(/\W+/, ' ').strip.gsub(/ +/, '_')
end
def column_for(field)
field_name = field.to_s.split('.').last
columns.detect { |c| c.name.to_s == field_name }
end
def type_cast_calculated_value(value, column, operation = nil)
operation = operation.to_s.downcase
case operation
when 'count' then value.to_i
when 'avg' then value.to_f
else column ? column.type_cast(value) : value
end
end
end
end
end
