Merge branch 'pluck-multiple-columns'

Allow ActiveRecord::Relation#pluck to accept multiple columns. Returns an
array of arrays containing the type casted values:

    Person.pluck(:id, :name)
    # SELECT people.id, people.name FROM people
    # [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']]

Closes rails#6500

activerecord/CHANGELOG.md

@@ -1,5 +1,14 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Allow ActiveRecord::Relation#pluck to accept multiple columns. Returns an
+    array of arrays containing the type casted values:
+
+        Person.pluck(:id, :name)
+        # SELECT people.id, people.name FROM people
+        # [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']]
+
+    *Jeroen van Ingen & Carlos Antonio da Silva*
+
 *   Improve the derivation of HABTM join table name to take account of nesting.
     It now takes the table names of the two models, sorts them lexically and
     then joins them, stripping any common prefix from the second table name.

activerecord/lib/active_record/relation/calculations.rb

@@ -107,7 +107,6 @@ def calculate(operation, column_name, options = {})
       relation = with_default_scope
 
       if relation.equal?(self)
-
         if has_include?(column_name)
           construct_relation_for_association_calculations.calculate(operation, column_name, options)
         else
@@ -139,6 +138,10 @@ def calculate(operation, column_name, options = {})
     #   # 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.uniq.pluck(:role)
     #   # SELECT DISTINCT role FROM people
     #   # => ['admin', 'member', 'guest']
@@ -151,30 +154,35 @@ def calculate(operation, column_name, options = {})
     #   # SELECT DATEDIFF(updated_at, created_at) FROM people
     #   # => ['0', '27761', '173']
     #
-    def pluck(column_name)
-      if column_name.is_a?(Symbol) && column_names.include?(column_name.to_s)
-        column_name = "#{table_name}.#{column_name}"
+    def pluck(*column_names)
+      column_names.map! do |column_name|
+        if column_name.is_a?(Symbol) && self.column_names.include?(column_name.to_s)
+          "#{table_name}.#{column_name}"
+        else
+          column_name
+        end
       end
 
-      if has_include?(column_name)
-        construct_relation_for_association_calculations.pluck(column_name)
+      if has_include?(column_names.first)
+        construct_relation_for_association_calculations.pluck(*column_names)
       else
-        result = klass.connection.select_all(select(column_name).arel, nil, bind_values)
-
-        key    = result.columns.first
-        column = klass.column_types.fetch(key) {
-          result.column_types.fetch(key) {
-            Class.new { def type_cast(v); v; end }.new
+        result  = klass.connection.select_all(select(column_names).arel, nil, bind_values)
+        columns = result.columns.map do |key|
+          klass.column_types.fetch(key) {
+            result.column_types.fetch(key) {
+              Class.new { def type_cast(v); v; end }.new
+            }
           }
-        }
-
-        result.map do |attributes|
-          raise ArgumentError, "Pluck expects to select just one attribute: #{attributes.inspect}" unless attributes.one?
+        end
 
-          value = klass.initialize_attributes(attributes).values.first
+        result = result.map do |attributes|
+          values = klass.initialize_attributes(attributes).values
 
-          column.type_cast(value)
+          columns.zip(values).map do |column, value|
+            column.type_cast(value)
+          end
         end
+        columns.one? ? result.map!(&:first) : result
       end
     end
 

activerecord/test/cases/calculations_test.rb

@@ -532,10 +532,6 @@ def test_pluck_with_selection_clause
     assert_equal [50 + 53 + 55 + 60], Account.pluck('SUM(DISTINCT(credit_limit)) as credit_limit')
   end
 
-  def test_pluck_expects_a_single_selection
-    assert_raise(ArgumentError) { Account.pluck 'id, credit_limit' }
-  end
-
   def test_plucks_with_ids
     assert_equal Company.all.map(&:id).sort, Company.ids.sort
   end
@@ -546,4 +542,29 @@ def test_pluck_not_auto_table_name_prefix_if_column_included
     assert_equal Company.count, ids.length
     assert_equal [7], ids.compact
   end
+
+  def test_pluck_multiple_columns
+    assert_equal [
+      [1, "The First Topic"], [2, "The Second Topic of the day"],
+      [3, "The Third Topic of the day"], [4, "The Fourth Topic of the day"]
+    ], Topic.order(:id).pluck(:id, :title)
+    assert_equal [
+      [1, "The First Topic", "David"], [2, "The Second Topic of the day", "Mary"],
+      [3, "The Third Topic of the day", "Carl"], [4, "The Fourth Topic of the day", "Carl"]
+    ], Topic.order(:id).pluck(:id, :title, :author_name)
+  end
+
+  def test_pluck_with_multiple_columns_and_selection_clause
+    assert_equal [[1, 50], [2, 50], [3, 50], [4, 60], [5, 55], [6, 53]],
+      Account.pluck('id, credit_limit')
+  end
+
+  def test_pluck_with_multiple_columns_and_includes
+    Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
+    companies_and_developers = Company.order('companies.id').includes(:contracts).pluck(:name, :developer_id)
+
+    assert_equal Company.count, companies_and_developers.length
+    assert_equal ["37signals", nil], companies_and_developers.first
+    assert_equal ["test", 7], companies_and_developers.last
+  end
 end

guides/source/active_record_querying.textile

@@ -609,8 +609,8 @@ And this will give you a single +Order+ object for each date where there are ord
 The SQL that would be executed would be something like this:
 
 <sql>
-SELECT date(created_at) as ordered_date, sum(price) as total_price 
-FROM orders 
+SELECT date(created_at) as ordered_date, sum(price) as total_price
+FROM orders
 GROUP BY date(created_at)
 </sql>
 
@@ -627,9 +627,9 @@ Order.select("date(created_at) as ordered_date, sum(price) as total_price").grou
 The SQL that would be executed would be something like this:
 
 <sql>
-SELECT date(created_at) as ordered_date, sum(price) as total_price 
-FROM orders 
-GROUP BY date(created_at) 
+SELECT date(created_at) as ordered_date, sum(price) as total_price
+FROM orders
+GROUP BY date(created_at)
 HAVING sum(price) > 100
 </sql>
 
@@ -1286,26 +1286,36 @@ Client.connection.select_all("SELECT * FROM clients WHERE id = '1'")
 
 h3. +pluck+
 
-<tt>pluck</tt> can be used to query a single column from the underlying table of a model. It accepts a column name as argument and returns an array of values of the specified column with the corresponding data type.
+<tt>pluck</tt> can be used to query a single or multiple columns from the underlying table of a model. It accepts a list of column names as argument and returns an array of values of the specified columns with the corresponding data type.
 
 <ruby>
 Client.where(:active => true).pluck(:id)
 # SELECT id FROM clients WHERE active = 1
+# => [1, 2, 3]
 
 Client.uniq.pluck(:role)
 # SELECT DISTINCT role FROM clients
+# => ['admin', 'member', 'guest']
+
+Client.pluck(:id, :name)
+# SELECT clients.id, clients.name FROM clients
+# => [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']]
 </ruby>
 
 +pluck+ makes it possible to replace code like
 
 <ruby>
 Client.select(:id).map { |c| c.id }
+# or
+Client.select(:id).map { |c| [c.id, c.name] }
 </ruby>
 
 with
 
 <ruby>
 Client.pluck(:id)
+# or
+Client.pluck(:id, :name)
 </ruby>
 
 h3. +ids+