Active Record Calculations
- A
- C
- I
- M
- P
- S
Instance Public methods
async_average(column_name) Link
Same as average
, but performs the query asynchronously and returns an ActiveRecord::Promise
.
async_count(column_name = nil) Link
Same as count
, but performs the query asynchronously and returns an ActiveRecord::Promise
.
async_ids() Link
Same as ids
, but performs the query asynchronously and returns an ActiveRecord::Promise
.
async_maximum(column_name) Link
Same as maximum
, but performs the query asynchronously and returns an ActiveRecord::Promise
.
async_minimum(column_name) Link
Same as minimum
, but performs the query asynchronously and returns an ActiveRecord::Promise
.
async_pick(*column_names) Link
Same as pick
, but performs the query asynchronously and returns an ActiveRecord::Promise
.
async_pluck(*column_names) Link
Same as pluck
, but performs the query asynchronously and returns an ActiveRecord::Promise
.
async_sum(identity_or_column = nil) Link
Same as sum
, but performs the query asynchronously and returns an ActiveRecord::Promise
.
average(column_name) Link
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
calculate(operation, column_name) Link
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 activerecord/lib/active_record/relation/calculations.rb, line 217 def calculate(operation, column_name) operation = operation.to_s.downcase if @none case operation when "count", "sum" result = group_values.any? ? Hash.new : 0 return @async ? Promise::Complete.new(result) : result when "average", "minimum", "maximum" result = group_values.any? ? Hash.new : nil return @async ? Promise::Complete.new(result) : result end end if has_include?(column_name) relation = apply_join_dependency if operation == "count" unless distinct_value || distinct_select?(column_name || select_for_count) relation.distinct! relation.select_values = Array(model.primary_key || table[Arel.star]) end # PostgreSQL: ORDER BY expressions must appear in SELECT list when using DISTINCT relation.order_values = [] if group_values.empty? end relation.calculate(operation, column_name) else perform_calculation(operation, column_name) end end
count(column_name = nil) Link
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", "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.
When given a block, loads all records in the relation, if the relation hasn’t been loaded yet. Calls the block with each record in the relation. Returns the number of records for which the block returns a truthy value.
Person.count { |person| person.age > 21 }
# => counts the number of people older that 21
Note: If there are a lot of records in the relation, loading all records could result in performance issues.
# File activerecord/lib/active_record/relation/calculations.rb, line 94 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
ids() Link
Returns the base model’s ID’s for the relation using the table’s primary key
Person.ids # SELECT people.id FROM people
Person.joins(:company).ids # SELECT people.id FROM people INNER JOIN companies ON companies.id = people.company_id
# File activerecord/lib/active_record/relation/calculations.rb, line 371 def ids primary_key_array = Array(primary_key) if loaded? result = records.map do |record| if primary_key_array.one? record._read_attribute(primary_key_array.first) else primary_key_array.map { |column| record._read_attribute(column) } end end return @async ? Promise::Complete.new(result) : result end if has_include?(primary_key) relation = apply_join_dependency.group(*primary_key_array) return relation.ids end columns = arel_columns(primary_key_array) relation = spawn relation.select_values = columns result = if relation.where_clause.contradiction? ActiveRecord::Result.empty else skip_query_cache_if_necessary do model.with_connection do |c| c.select_all(relation, "#{model.name} Ids", async: @async) end end end result.then { |result| type_cast_pluck_values(result, columns) } end
maximum(column_name) Link
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
minimum(column_name) Link
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
pick(*column_names) Link
Pick the value(s) from the named column(s) in the current relation. This is short-hand for relation.limit(1).pluck(*column_names).first
, 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' ]
# File activerecord/lib/active_record/relation/calculations.rb, line 352 def pick(*column_names) if loaded? && all_attributes?(column_names) result = records.pick(*column_names) return @async ? Promise::Complete.new(result) : result end limit(1).pluck(*column_names).then(&:first) end
pluck(*column_names) Link
Use pluck
as a shortcut to select one or more attributes without loading an entire record object per row.
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]
Comment.joins(:person).pluck(:id, person: :id)
# SELECT comments.id, person.id FROM comments INNER JOIN people person ON person.id = comments.person_id
# => [[1, 2], [2, 2]]
Comment.joins(:person).pluck(:id, person: [:id, :name])
# SELECT comments.id, person.id, person.name FROM comments INNER JOIN people person ON person.id = comments.person_id
# => [[1, 2, 'David'], [2, 2, 'David']]
Person.pluck(Arel.sql('DATEDIFF(updated_at, created_at)'))
# SELECT DATEDIFF(updated_at, created_at) FROM people
# => ['0', '27761', '173']
See also ids
.
# File activerecord/lib/active_record/relation/calculations.rb, line 291 def pluck(*column_names) if @none if @async return Promise::Complete.new([]) else return [] end end if loaded? && all_attributes?(column_names) result = records.pluck(*column_names) if @async return Promise::Complete.new(result) else return result end end if has_include?(column_names.first) relation = apply_join_dependency relation.pluck(*column_names) else model.disallow_raw_sql!(flattened_args(column_names)) relation = spawn columns = relation.arel_columns(column_names) relation.select_values = columns result = skip_query_cache_if_necessary do if where_clause.contradiction? ActiveRecord::Result.empty(async: @async) else model.with_connection do |c| c.select_all(relation.arel, "#{model.name} Pluck", async: @async) end end end result.then do |result| type_cast_pluck_values(result, columns) end end end
sum(initial_value_or_column = 0, &block) Link
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
When given a block, loads all records in the relation, if the relation hasn’t been loaded yet. Calls the block with each record in the relation. Returns the sum of initial_value_or_column
and the block return values:
Person.sum { |person| person.age } # => 4562
Person.sum(1000) { |person| person.age } # => 5562
Note: If there are a lot of records in the relation, loading all records could result in performance issues.