module ActiveRecord module Calculations # Count the records. # # Person.count # # => the total count of all people # # Person.count(:age) # # => returns the total count of all people whose age is present in database # # Person.count(:all) # # => performs a COUNT(*) (:all is an alias for '*') # # Person.distinct.count(:age) # # => counts the number of different age values # # If #count is used with {Relation#group}[rdoc-ref:QueryMethods#group], # it returns a Hash whose keys represent the aggregated column, # and the values are the respective amounts: # # Person.group(:city).count # # => { 'Rome' => 5, 'Paris' => 3 } # # If #count is used with {Relation#group}[rdoc-ref:QueryMethods#group] for multiple columns, it returns a Hash whose # keys are an array containing the individual values of each column and the value # of each key would be the #count. # # Article.group(:status, :category).count # # => {["draft", "business"]=>10, ["draft", "technology"]=>4, # ["published", "business"]=>0, ["published", "technology"]=>2} # # If #count is used with {Relation#select}[rdoc-ref:QueryMethods#select], it will count the selected columns: # # Person.select(:age).count # # => counts the number of different age values # # Note: not all valid {Relation#select}[rdoc-ref:QueryMethods#select] expressions are valid #count expressions. The specifics differ # between databases. In invalid cases, an error from the database is thrown. def count(column_name = nil) return super() if block_given? calculate(:count, column_name) end # Calculates the average value on a given column. Returns +nil+ if there's # no row. See #calculate for examples with options. # # Person.average(:age) # => 35.8 def average(column_name) calculate(:average, column_name) 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) calculate(:minimum, column_name) 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) calculate(:maximum, column_name) 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 = nil) return super() if block_given? calculate(:sum, column_name) end # This calculates aggregate values in the given column. Methods for #count, #sum, #average, # #minimum, and #maximum have been added as shortcuts. # # Person.calculate(:count, :all) # The same as Person.count # Person.average(:age) # SELECT AVG(age) FROM people... # # # Selects the minimum age for any family without any minors # Person.group(:last_name).having("min(age) > 17").minimum(:age) # # Person.sum("2 * age") # # There are two basic forms of output: # # * Single aggregate value: The single value is type cast to Integer 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. It # takes either a column name, or the name of a belongs_to association. # # values = Person.group('last_name').maximum(:age) # puts values["Drake"] # # => 43 # # drake = Family.find_by(last_name: 'Drake') # values = Person.group(:family).maximum(:age) # Person belongs_to :family # puts values[drake] # # => 43 # # values.each do |family, max_age| # ... # end def calculate(operation, column_name) if has_include?(column_name) relation = construct_relation_for_association_calculations relation = relation.distinct if operation.to_s.downcase == "count" relation.calculate(operation, column_name) else perform_calculation(operation, column_name) end end # Use #pluck as a shortcut to select one or more attributes without # loading a bunch of records just to grab the attributes you want. # # Person.pluck(:name) # # instead of # # Person.all.map(&:name) # # Pluck returns an Array of attribute values type-casted to match # the plucked column names, if they can be deduced. Plucking an SQL fragment # returns String values by default. # # Person.pluck(:name) # # SELECT people.name FROM people # # => ['David', 'Jeremy', 'Jose'] # # Person.pluck(:id, :name) # # SELECT people.id, people.name FROM people # # => [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']] # # Person.distinct.pluck(:role) # # SELECT DISTINCT role FROM people # # => ['admin', 'member', 'guest'] # # Person.where(age: 21).limit(5).pluck(:id) # # SELECT people.id FROM people WHERE people.age = 21 LIMIT 5 # # => [2, 3] # # Person.pluck('DATEDIFF(updated_at, created_at)') # # SELECT DATEDIFF(updated_at, created_at) FROM people # # => ['0', '27761', '173'] # # See also #ids. # def pluck(*column_names) if loaded? && (column_names.map(&:to_s) - @klass.attribute_names - @klass.attribute_aliases.keys).empty? return records.pluck(*column_names) end if has_include?(column_names.first) construct_relation_for_association_calculations.pluck(*column_names) else relation = spawn relation.select_values = column_names.map { |cn| @klass.has_attribute?(cn) || @klass.attribute_alias?(cn) ? arel_attribute(cn) : cn } result = klass.connection.select_all(relation.arel, nil, bound_attributes) result.cast_values(klass.attribute_types) end end # Pluck all the ID's for the relation using the table's primary key # # Person.ids # SELECT people.id FROM people # Person.joins(:companies).ids # SELECT people.id FROM people INNER JOIN companies ON companies.person_id = people.id def ids pluck primary_key end private def has_include?(column_name) eager_loading? || (includes_values.present? && column_name && column_name != :all) end def perform_calculation(operation, column_name) operation = operation.to_s.downcase # If #count is used with #distinct (i.e. `relation.distinct.count`) it is # considered distinct. distinct = distinct_value if operation == "count" column_name ||= select_for_count column_name = primary_key if column_name == :all && distinct distinct = nil if column_name =~ /\s*DISTINCT[\s(]+/i end if group_values.any? execute_grouped_calculation(operation, column_name, distinct) else execute_simple_calculation(operation, column_name, distinct) end end def aggregate_column(column_name) return column_name if Arel::Expressions === column_name if @klass.has_attribute?(column_name.to_s) || @klass.attribute_alias?(column_name.to_s) @klass.arel_attribute(column_name) else Arel.sql(column_name == :all ? "*" : column_name.to_s) end end def operation_over_aggregate_column(column, operation, distinct) operation == "count" ? column.count(distinct) : column.send(operation) end def execute_simple_calculation(operation, column_name, distinct) #:nodoc: column_alias = column_name if operation == "count" && (limit_value || offset_value) # Shortcut when limit is zero. return 0 if limit_value == 0 query_builder = build_count_subquery(spawn, column_name, distinct) else # PostgreSQL doesn't like ORDER BY when there are no GROUP BY relation = unscope(:order).distinct!(false) column = aggregate_column(column_name) select_value = operation_over_aggregate_column(column, operation, distinct) column_alias = select_value.alias column_alias ||= @klass.connection.column_name_for_operation(operation, select_value) relation.select_values = [select_value] query_builder = relation.arel end result = @klass.connection.select_all(query_builder, nil, bound_attributes) row = result.first value = row && row.values.first type = result.column_types.fetch(column_alias) do type_for(column_name) end type_cast_calculated_value(value, type, operation) end def execute_grouped_calculation(operation, column_name, distinct) #:nodoc: group_attrs = group_values if group_attrs.first.respond_to?(:to_sym) association = @klass._reflect_on_association(group_attrs.first) associated = group_attrs.size == 1 && association && association.belongs_to? # only count belongs_to associations group_fields = Array(associated ? association.foreign_key : group_attrs) else group_fields = group_attrs end group_fields = arel_columns(group_fields) group_aliases = group_fields.map { |field| column_alias_for(field) } group_columns = group_aliases.zip(group_fields) if operation == "count" && column_name == :all aggregate_alias = "count_all" else aggregate_alias = column_alias_for([operation, column_name].join(" ")) end select_values = [ operation_over_aggregate_column( aggregate_column(column_name), operation, distinct).as(aggregate_alias) ] select_values += self.select_values unless having_clause.empty? select_values.concat group_columns.map { |aliaz, field| if field.respond_to?(:as) field.as(aliaz) else "#{field} AS #{aliaz}" end } relation = except(:group).distinct!(false) relation.group_values = group_fields relation.select_values = select_values calculated_data = @klass.connection.select_all(relation, nil, relation.bound_attributes) if association key_ids = calculated_data.collect { |row| row[group_aliases.first] } key_records = association.klass.base_class.where(association.klass.base_class.primary_key => key_ids) key_records = Hash[key_records.map { |r| [r.id, r] }] end Hash[calculated_data.map do |row| key = group_columns.map { |aliaz, col_name| type = type_for(col_name) do calculated_data.column_types.fetch(aliaz, Type.default_value) end type_cast_calculated_value(row[aliaz], type) } key = key.first if key.size == 1 key = key_records[key] if associated type = calculated_data.column_types.fetch(aggregate_alias) { type_for(column_name) } [key, type_cast_calculated_value(row[aggregate_alias], type, operation)] end] end # Converts the given keys to the value that the database adapter returns as # a usable column name: # # column_alias_for("users.id") # => "users_id" # column_alias_for("sum(id)") # => "sum_id" # column_alias_for("count(distinct users.id)") # => "count_distinct_users_id" # column_alias_for("count(*)") # => "count_all" def column_alias_for(keys) if keys.respond_to? :name keys = "#{keys.relation.name}.#{keys.name}" end table_name = keys.to_s.downcase table_name.gsub!(/\*/, "all") table_name.gsub!(/\W+/, " ") table_name.strip! table_name.gsub!(/ +/, "_") @klass.connection.table_alias_for(table_name) end def type_for(field, &block) field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split(".").last @klass.type_for_attribute(field_name, &block) end def type_cast_calculated_value(value, type, operation = nil) case operation when "count" then value.to_i when "sum" then type.deserialize(value || 0) when "average" then value.respond_to?(:to_d) ? value.to_d : value else type.deserialize(value) end end def select_for_count if select_values.present? return select_values.first if select_values.one? select_values.join(", ") else :all end end def build_count_subquery(relation, column_name, distinct) column_alias = Arel.sql("count_column") subquery_alias = Arel.sql("subquery_for_count") aliased_column = aggregate_column(column_name == :all ? 1 : column_name).as(column_alias) relation.select_values = [aliased_column] subquery = relation.arel.as(subquery_alias) sm = Arel::SelectManager.new relation.engine select_value = operation_over_aggregate_column(column_alias, "count", distinct) sm.project(select_value).from(subquery) end end end