module ActiveRecord::Calculations

Public Instance Methods

average(column_name) click to toggle source

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 58
def average(column_name)
  calculate(:average, column_name)
end
calculate(operation, column_name) click to toggle source

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
# File lib/active_record/relation/calculations.rb, line 130
def calculate(operation, column_name)
  if has_include?(column_name)
    relation = apply_join_dependency

    if operation.to_s.downcase == "count"
      relation.distinct!
      # PostgreSQL: ORDER BY expressions must appear in SELECT list when using DISTINCT
      if (column_name == :all || column_name.nil?) && select_values.empty?
        relation.order_values = []
      end
    end

    relation.calculate(operation, column_name)
  else
    perform_calculation(operation, column_name)
  end
end
count(column_name = nil) click to toggle source

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, 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 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, it will count the selected columns:

Person.select(:age).count
# => counts the number of different age values

Note: not all valid Relation#select expressions are valid count expressions. The specifics differ between databases. In invalid cases, an error from the database is thrown.

Calls superclass method
# File lib/active_record/relation/calculations.rb, line 40
def count(column_name = nil)
  if block_given?
    unless column_name.nil?
      ActiveSupport::Deprecation.warn \
        "When `count' is called with a block, it ignores other arguments. " \
        "This behavior is now deprecated and will result in an ArgumentError in Rails 6.0."
    end

    return super()
  end

  calculate(:count, column_name)
end
ids() click to toggle source

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 206
def ids
  pluck primary_key
end
maximum(column_name) click to toggle source

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 76
def maximum(column_name)
  calculate(:maximum, column_name)
end
minimum(column_name) click to toggle source

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 67
def minimum(column_name)
  calculate(:minimum, column_name)
end
pluck(*column_names) click to toggle source

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.

# File lib/active_record/relation/calculations.rb, line 183
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)
    relation = apply_join_dependency
    relation.pluck(*column_names)
  else
    enforce_raw_sql_whitelist(column_names)
    relation = spawn
    relation.select_values = column_names.map { |cn|
      @klass.has_attribute?(cn) || @klass.attribute_alias?(cn) ? arel_attribute(cn) : cn
    }
    result = skip_query_cache_if_necessary { klass.connection.select_all(relation.arel, nil) }
    result.cast_values(klass.attribute_types)
  end
end
sum(column_name = nil) click to toggle source

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
Calls superclass method
# File lib/active_record/relation/calculations.rb, line 85
def sum(column_name = nil)
  if block_given?
    unless column_name.nil?
      ActiveSupport::Deprecation.warn \
        "When `sum' is called with a block, it ignores other arguments. " \
        "This behavior is now deprecated and will result in an ArgumentError in Rails 6.0."
    end

    return super()
  end

  calculate(:sum, column_name)
end

Private Instance Methods

aggregate_column(column_name) click to toggle source
# File lib/active_record/relation/calculations.rb, line 241
def aggregate_column(column_name)
  return column_name if Arel::Expressions === column_name

  if @klass.has_attribute?(column_name) || @klass.attribute_alias?(column_name)
    @klass.arel_attribute(column_name)
  else
    Arel.sql(column_name == :all ? "*" : column_name.to_s)
  end
end
build_count_subquery(relation, column_name, distinct) click to toggle source
# File lib/active_record/relation/calculations.rb, line 399
def build_count_subquery(relation, column_name, distinct)
  if column_name == :all
    relation.select_values = [ Arel.sql(FinderMethods::ONE_AS_ONE) ] unless distinct
  else
    column_alias = Arel.sql("count_column")
    relation.select_values = [ aggregate_column(column_name).as(column_alias) ]
  end

  subquery = relation.arel.as(Arel.sql("subquery_for_count"))
  select_value = operation_over_aggregate_column(column_alias || Arel.star, "count", false)

  Arel::SelectManager.new(subquery).project(select_value)
end
column_alias_for(keys) click to toggle source

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"
# File lib/active_record/relation/calculations.rb, line 362
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
has_include?(column_name) click to toggle source
# File lib/active_record/relation/calculations.rb, line 212
def has_include?(column_name)
  eager_loading? || (includes_values.present? && column_name && column_name != :all)
end
operation_over_aggregate_column(column, operation, distinct) click to toggle source
# File lib/active_record/relation/calculations.rb, line 251
def operation_over_aggregate_column(column, operation, distinct)
  operation == "count" ? column.count(distinct) : column.send(operation)
end
perform_calculation(operation, column_name) click to toggle source
# File lib/active_record/relation/calculations.rb, line 216
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
    if column_name == :all
      if distinct && (group_values.any? || select_values.empty? && order_values.empty?)
        column_name = primary_key
      end
    elsif column_name =~ /\s*DISTINCT[\s(]+/i
      distinct = nil
    end
  end

  if group_values.any?
    execute_grouped_calculation(operation, column_name, distinct)
  else
    execute_simple_calculation(operation, column_name, distinct)
  end
end
select_for_count() click to toggle source
# File lib/active_record/relation/calculations.rb, line 390
def select_for_count
  if select_values.present?
    return select_values.first if select_values.one?
    select_values.join(", ")
  else
    :all
  end
end
type_cast_calculated_value(value, type, operation = nil) click to toggle source
# File lib/active_record/relation/calculations.rb, line 381
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
type_for(field, &block) click to toggle source
# File lib/active_record/relation/calculations.rb, line 376
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