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# frozen_string_literal: true
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)
if block_given?
unless column_name.nil?
raise ArgumentError, "Column name argument is not supported when a block is passed."
end
super()
else
calculate(:count, column_name)
end
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)
if block_given?
unless column_name.nil?
raise ArgumentError, "Column name argument is not supported when a block is passed."
end
super()
else
calculate(:sum, column_name)
end
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 = apply_join_dependency
if operation.to_s.downcase == "count"
unless distinct_value || distinct_select?(column_name || select_for_count)
relation.distinct!
relation.select_values = [ klass.primary_key || table[Arel.star] ]
end
# PostgreSQL: ORDER BY expressions must appear in SELECT list when using DISTINCT
relation.order_values = []
end
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)
relation = apply_join_dependency
relation.pluck(*column_names)
else
klass.disallow_raw_sql!(column_names)
relation = spawn
relation.select_values = column_names
result = skip_query_cache_if_necessary { klass.connection.select_all(relation.arel, nil) }
result.cast_values(klass.attribute_types)
end
end
# Pick the value(s) from the named column(s) in the current relation.
# This is short-hand for <tt>relation.limit(1).pluck(*column_names).first</tt>, and is primarily useful
# when you have a relation that's already narrowed down to a single row.
#
# Just like #pluck, #pick will only load the actual value, not the entire record object, so it's also
# more efficient. The value is, again like with pluck, typecast by the column type.
#
# Person.where(id: 1).pick(:name)
# # SELECT people.name FROM people WHERE id = 1 LIMIT 1
# # => 'David'
#
# Person.where(id: 1).pick(:name, :email_address)
# # SELECT people.name, people.email_address FROM people WHERE id = 1 LIMIT 1
# # => [ 'David', 'david@loudthinking.com' ]
def pick(*column_names)
limit(1).pluck(*column_names).first
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
if column_name == :all
if !distinct
distinct = distinct_select?(select_for_count) if group_values.empty?
elsif group_values.any? || select_values.empty? && order_values.empty?
column_name = primary_key
end
elsif distinct_select?(column_name)
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
def distinct_select?(column_name)
column_name.is_a?(::String) && /\bDISTINCT[\s(]/i.match?(column_name)
end
def aggregate_column(column_name)
return column_name if Arel::Expressions === column_name
arel_column(column_name.to_s) do |name|
Arel.sql(column_name == :all ? "*" : name)
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" && (column_name == :all && distinct || has_limit_or_offset?)
# 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)
if operation == "sum" && distinct
select_value.distinct = true
end
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 = skip_query_cache_if_necessary { @klass.connection.select_all(query_builder, nil) }
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_fields = group_values
if group_fields.size == 1 && group_fields.first.respond_to?(:to_sym)
association = klass._reflect_on_association(group_fields.first)
associated = association && association.belongs_to? # only count belongs_to associations
group_fields = Array(association.foreign_key) if associated
end
group_fields = arel_columns(group_fields)
group_aliases = group_fields.map { |field|
field = connection.visitor.compile(field) if Arel.arel_node?(field)
column_alias_for(field.to_s.downcase)
}
group_columns = group_aliases.zip(group_fields)
aggregate_alias = column_alias_for("#{operation} #{column_name.to_s.downcase}")
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 = skip_query_cache_if_necessary { @klass.connection.select_all(relation.arel, nil) }
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 field 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(field)
column_alias = +field
column_alias.gsub!(/\*/, "all")
column_alias.gsub!(/\W+/, " ")
column_alias.strip!
column_alias.gsub!(/ +/, "_")
connection.table_alias_for(column_alias)
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)
if column_name == :all
column_alias = Arel.star
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_alias = Arel.sql("subquery_for_count")
select_value = operation_over_aggregate_column(column_alias, "count", false)
relation.build_subquery(subquery_alias, select_value)
end
end
end
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