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
# File lib/active_record/relation/calculations.rb, line 31 def average(column_name, options = {}) calculate(:average, 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.
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. 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 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")
# File lib/active_record/relation/calculations.rb, line 101 def calculate(operation, column_name, options = {}) relation = with_default_scope if relation.equal?(self) if has_include?(column_name) construct_relation_for_association_calculations.calculate(operation, column_name, options) else perform_calculation(operation, column_name, options) end else relation.calculate(operation, column_name, options) end rescue ThrowResult 0 end
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 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 }
# File lib/active_record/relation/calculations.rb, line 22 def count(column_name = nil, options = {}) column_name, options = nil, column_name if column_name.is_a?(Hash) calculate(:count, column_name, options) 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
# File lib/active_record/relation/calculations.rb, line 188 def ids pluck primary_key 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
# File lib/active_record/relation/calculations.rb, line 49 def maximum(column_name, options = {}) calculate(:maximum, 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
# File lib/active_record/relation/calculations.rb, line 40 def minimum(column_name, options = {}) calculate(:minimum, column_name, options) 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(:id) # SELECT people.id FROM people # => [1, 2, 3] Person.pluck(:id, :name) # SELECT people.id, people.name FROM people # => [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']] Person.pluck('DISTINCT 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']
# File lib/active_record/relation/calculations.rb, line 150 def pluck(*column_names) column_names.map! do |column_name| if column_name.is_a?(Symbol) && self.column_names.include?(column_name.to_s) "#{connection.quote_table_name(table_name)}.#{connection.quote_column_name(column_name)}" else column_name end end if has_include?(column_names.first) construct_relation_for_association_calculations.pluck(*column_names) else relation = spawn relation.select_values = column_names result = klass.connection.select_all(relation.arel, nil, bind_values) columns = result.columns.map do |key| klass.column_types.fetch(key) { result.column_types.fetch(key) { Class.new { def type_cast(v); v; end }.new } } end result = result.map do |attributes| values = klass.initialize_attributes(attributes).values columns.zip(values).map do |column, value| column.type_cast(value) end end columns.one? ? result.map!(&:first) : result end 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
# File lib/active_record/relation/calculations.rb, line 58 def sum(*args) if block_given? ActiveSupport::Deprecation.warn( "Calling #sum with a block is deprecated and will be removed in Rails 4.1. " "If you want to perform sum calculation over the array of elements, use `to_a.sum(&block)`." ) self.to_a.sum(*args) {|*block_args| yield(*block_args)} else calculate(:sum, *args) end end
# File lib/active_record/relation/calculations.rb, line 168 def type_cast(v); v; end
# File lib/active_record/relation/calculations.rb, line 228 def aggregate_column(column_name) if @klass.column_names.include?(column_name.to_s) Arel::Attribute.new(@klass.unscoped.table, column_name) else Arel.sql(column_name == :all ? "*" : column_name.to_s) end end
# File lib/active_record/relation/calculations.rb, line 387 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
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" column_alias_for("count", "id") # => "count_id"
# File lib/active_record/relation/calculations.rb, line 347 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
# File lib/active_record/relation/calculations.rb, line 361 def column_for(field) field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split('.').last @klass.columns_hash[field_name] end
# File lib/active_record/relation/calculations.rb, line 194 def has_include?(column_name) eager_loading? || (includes_values.present? && (column_name || references_eager_loaded_tables?)) end
# File lib/active_record/relation/calculations.rb, line 236 def operation_over_aggregate_column(column, operation, distinct) operation == 'count' ? column.count(distinct) : column.send(operation) end
# File lib/active_record/relation/calculations.rb, line 198 def perform_calculation(operation, column_name, options = {}) operation = operation.to_s.downcase # If #count is used with #distinct / #uniq it is considered distinct. (eg. relation.distinct.count) distinct = self.distinct_value if options.has_key?(:distinct) ActiveSupport::Deprecation.warn "The :distinct option for `Relation#count` is deprecated. " "Please use `Relation#distinct` instead. (eg. `relation.distinct.count`)" distinct = options[:distinct] end if operation == "count" column_name ||= (select_for_count || :all) unless arel.ast.grep(Arel::Nodes::OuterJoin).empty? distinct = true end column_name = primary_key if column_name == :all && distinct distinct = nil if column_name =~ /\s*DISTINCT\s+/ end if group_values.any? execute_grouped_calculation(operation, column_name, distinct) else execute_simple_calculation(operation, column_name, distinct) end end
TODO: refactor to allow non-string `select_values` (eg. Arel nodes).
# File lib/active_record/relation/calculations.rb, line 380 def select_for_count if select_values.present? select = select_values.join(", ") select if select !~ /[,*]/ end end
# File lib/active_record/relation/calculations.rb, line 366 def type_cast_calculated_value(value, column, operation = nil) case operation when 'count' then value.to_i when 'sum' then type_cast_using_column(value || 0, column) when 'average' then value.respond_to?(:to_d) ? value.to_d : value else type_cast_using_column(value, column) end end
# File lib/active_record/relation/calculations.rb, line 375 def type_cast_using_column(value, column) column ? column.type_cast(value) : value end