instance method `pluck`

Ruby on Rails 4.1.16

Since v3.2.22.5

Available in: v3.2.22.5 v4.0.13 v4.1.16 v4.2.9 v5.2.8.1 v6.0.6 v6.1.7.10 v7.0.10 v7.1.6 v7.2.3 v8.0.4 v8.1.2

Compare with:

pluck(*column_names)

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']

Parameters

column_names rest

Source

# File activerecord/lib/active_record/relation/calculations.rb, line 156
    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, bind_values)
        columns = result.columns.map do |key|
          klass.column_types.fetch(key) {
            result.column_types.fetch(key) { result.identity_type }
          }
        end

        result = result.rows.map do |values|
          values = result.columns.zip(values).map do |column_name, value|
            single_attr_hash = { column_name => value }
            klass.initialize_attributes(single_attr_hash).values.first
          end

          columns.zip(values).map { |column, value| column.type_cast value }
        end
        columns.one? ? result.map!(&:first) : result
      end
    end

Defined in activerecord/lib/active_record/relation/calculations.rb line 156 · View on GitHub · Improve this page · Find usages on GitHub

Defined in ActiveRecord::Calculations

Signature

Parameters