module ActiveRecord module Calculations #:nodoc: CALCULATIONS_OPTIONS = [:conditions, :joins, :order, :select, :group, :having, :distinct, :limit, :offset, :include] 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: # # * :conditions: An SQL fragment like "administrator = 1" or [ "user_name = ?", username ]. See conditions in the intro. # * :joins: 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. # * :include: 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. # * :order: An SQL fragment like "created_at DESC, name" (really only used with GROUP BY calculations). # * :group: An attribute name by which the result should be grouped. Uses the GROUP BY SQL-clause. # * :select: 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. # * :distinct: 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) calculate(:count, *construct_count_options_from_legacy_args(*args)) 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: # * :conditions: An SQL fragment like "administrator = 1" or [ "user_name = ?", username ]. See conditions in the intro. # * :joins: 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. # * :order: An SQL fragment like "created_at DESC, name" (really only used with GROUP BY calculations). # * :group: An attribute name by which the result should be grouped. Uses the GROUP BY SQL-clause. # * :select: 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. # * :distinct: 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 catch :invalid_query do if options[:group] return execute_grouped_calculation(operation, column_name, column, options) else return execute_simple_calculation(operation, column_name, column, options) end end 0 end protected def construct_count_options_from_legacy_args(*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 [column_name, options] end def construct_calculation_sql(operation, column_name, options) #:nodoc: scope = scope(:find) merged_includes = merge_includes(scope ? scope[:include] : [], options[:include]) aggregate_alias = column_alias_for(operation, column_name) use_workaround = !Base.connection.supports_count_distinct? && options[:distinct] && operation.to_s.downcase == 'count' join_dependency = nil if merged_includes.any? && operation.to_s.downcase == 'count' options[:distinct] = true column_name = [table_name, primary_key] * '.' end sql = "SELECT #{operation}(#{'DISTINCT ' if options[:distinct]}#{column_name}) AS #{aggregate_alias}" # A (slower) workaround if we're using a backend, like sqlite, that doesn't support COUNT DISTINCT. sql = "SELECT COUNT(*) AS #{aggregate_alias}" if use_workaround sql << ", #{options[:group_field]} AS #{options[:group_alias]}" if options[:group] sql << " FROM (SELECT DISTINCT #{column_name}" if use_workaround sql << " FROM #{table_name} " if merged_includes.any? join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(self, merged_includes, options[:joins]) sql << join_dependency.join_associations.collect{|join| join.association_join }.join end add_joins!(sql, options, scope) add_conditions!(sql, options[:conditions], scope) add_limited_ids_condition!(sql, options, join_dependency) if join_dependency && !using_limitable_reflections?(join_dependency.reflections) && ((scope && scope[:limit]) || options[:limit]) 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, scope) sql << ')' if use_workaround sql end def execute_simple_calculation(operation, column_name, column, options) #:nodoc: value = connection.select_value(construct_calculation_sql(operation, column_name, options)) type_cast_calculated_value(value, column, operation) end def execute_grouped_calculation(operation, column_name, column, 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(operation, column_name, options.merge(:group_field => group_field, :group_alias => group_alias)) calculated_data = connection.select_all(sql) aggregate_alias = column_alias_for(operation, column_name) 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 = {}) options.assert_valid_keys(CALCULATIONS_OPTIONS) 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) connection.table_alias_for(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