module ActiveRecord::Calculations
Public Instance Methods
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 49 def average(column_name, options = {}) # TODO: Remove options argument as soon we remove support to # activerecord-deprecated_finders. 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 117 def calculate(operation, column_name, options = {}) # TODO: Remove options argument as soon we remove support to # activerecord-deprecated_finders. if column_name.is_a?(Symbol) && attribute_alias?(column_name) column_name = attribute_alias(column_name) end if has_include?(column_name) construct_relation_for_association_calculations.calculate(operation, column_name, options) else perform_calculation(operation, column_name, options) end 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 }
If count
is used with 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 select
, it will count the
selected columns:
Person.select(:age).count # => counts the number of different age values
Note: not all valid select
expressions are valid
count
expressions. The specifics differ between databases. In
invalid cases, an error from the database is thrown.
# File lib/active_record/relation/calculations.rb, line 38 def count(column_name = nil, options = {}) # TODO: Remove options argument as soon we remove support to # activerecord-deprecated_finders. 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 189 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 71 def maximum(column_name, options = {}) # TODO: Remove options argument as soon we remove support to # activerecord-deprecated_finders. 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 60 def minimum(column_name, options = {}) # TODO: Remove options argument as soon we remove support to # activerecord-deprecated_finders. 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 164 def pluck(*column_names) column_names.map! do |column_name| if column_name.is_a?(Symbol) && attribute_alias?(column_name) attribute_alias(column_name) else column_name.to_s end 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| columns_hash.key?(cn) ? arel_table[cn] : cn } result = klass.connection.select_all(relation.arel, nil, relation.arel.bind_values + bind_values) result.cast_values(klass.column_types) 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 82 def sum(*args) calculate(:sum, *args) end
Private Instance Methods
# File lib/active_record/relation/calculations.rb, line 225 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 388 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] arel = relation.arel subquery = arel.as(subquery_alias) sm = Arel::SelectManager.new relation.engine sm.bind_values = arel.bind_values 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 351 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 195 def has_include?(column_name) eager_loading? || (includes_values.present? && ((column_name && column_name != :all) || references_eager_loaded_tables?)) end
# File lib/active_record/relation/calculations.rb, line 233 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 199 def perform_calculation(operation, column_name, options = {}) # TODO: Remove options argument as soon we remove support to # activerecord-deprecated_finders. 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 operation == "count" column_name ||= select_for_count 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(]+/i 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_values.join(", ") else :all end end
# File lib/active_record/relation/calculations.rb, line 370 def type_cast_calculated_value(value, type, operation = nil) case operation when 'count' then value.to_i when 'sum' then type.type_cast_from_database(value || 0) when 'average' then value.respond_to?(:to_d) ? value.to_d : value else type.type_cast_from_database(value) end end
# File lib/active_record/relation/calculations.rb, line 365 def type_for(field) field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split('.').last @klass.type_for_attribute(field_name) end