Allow ActiveRecord::Base#pluck to accept hash values

Author: fatkodima

activerecord/CHANGELOG.md

@@ -1,3 +1,15 @@
+*   Allow `ActiveRecord::Base#pluck` to accept hash values
+
+    ```ruby
+    # Before
+    Post.joins(:comments).pluck("posts.id", "comments.id", "comments.body")
+
+    # After
+    Post.joins(:comments).pluck(posts: [:id], comments: [:id, :body])
+    ```
+
+    *fatkodima*
+
 *   Raise an `ActiveRecord::ActiveRecordError` error when the MySQL database returns an invalid version string.
 
     *Kevin McPhillips*

activerecord/lib/active_record/relation/calculations.rb

@@ -275,6 +275,10 @@ def calculate(operation, column_name)
     #   # SELECT people.id FROM people WHERE people.age = 21 LIMIT 5
     #   # => [2, 3]
     #
+    #   Comment.joins(:person).pluck(:id, person: [:id])
+    #   # SELECT comments.id, people.id FROM comments INNER JOIN people on comments.person_id = people.id
+    #   # => [[1, 2], [2, 2]]
+    #
     #   Person.pluck(Arel.sql('DATEDIFF(updated_at, created_at)'))
     #   # SELECT DATEDIFF(updated_at, created_at) FROM people
     #   # => ['0', '27761', '173']
@@ -302,7 +306,7 @@ def pluck(*column_names)
         relation = apply_join_dependency
         relation.pluck(*column_names)
       else
-        klass.disallow_raw_sql!(column_names.flatten)
+        klass.disallow_raw_sql!(flattened_args(column_names))
         columns = arel_columns(column_names)
         relation = spawn
         relation.select_values = columns

activerecord/lib/active_record/relation/query_methods.rb

@@ -1854,6 +1854,8 @@ def arel_columns(columns)
             arel_column(field, &:itself)
           when Proc
             field.call
+          when Hash
+            arel_columns_from_hash(field)
           else
             field
           end
@@ -1944,8 +1946,8 @@ def validate_order_args(args)
         end
       end
 
-      def flattened_args(order_args)
-        order_args.flat_map { |e| (e.is_a?(Hash) || e.is_a?(Array)) ? flattened_args(e.to_a) : e }
+      def flattened_args(args)
+        args.flat_map { |e| (e.is_a?(Hash) || e.is_a?(Array)) ? flattened_args(e.to_a) : e }
       end
 
       def preprocess_order_args(order_args)
@@ -2081,14 +2083,14 @@ def check_if_method_has_arguments!(method_name, args, message = nil)
       def process_select_args(fields)
         fields.flat_map do |field|
           if field.is_a?(Hash)
-            transform_select_hash_values(field)
+            arel_columns_from_hash(field)
           else
             field
           end
         end
       end
 
-      def transform_select_hash_values(fields)
+      def arel_columns_from_hash(fields)
         fields.flat_map do |key, columns_aliases|
           case columns_aliases
           when Hash

activerecord/test/cases/calculations_test.rb

@@ -952,6 +952,30 @@ def test_pluck_with_selection_clause
     assert_equal [50 + 53 + 55 + 60], Account.pluck(Arel.sql("SUM(DISTINCT(credit_limit))"))
   end
 
+  def test_pluck_with_hash_argument
+    expected = [
+      [1, "The First Topic"],
+      [2, "The Second Topic of the day"],
+      [3, "The Third Topic of the day"]
+    ]
+    assert_equal expected, Topic.order(:id).limit(3).pluck(:id, topics: [:title])
+  end
+
+  def test_pluck_with_hash_argument_with_multiple_tables
+    expected = [
+      [1, 1, "Thank you for the welcome"],
+      [1, 2, "Thank you again for the welcome"],
+      [2, 3, "Don't think too hard"]
+    ]
+    assert_equal expected, Post.joins(:comments).order(posts: { id: :asc }, comments: { id: :asc }).limit(3).pluck(posts: [:id], comments: [:id, :body])
+  end
+
+  def test_pluck_with_hash_argument_containing_non_existent_field
+    assert_raises(ActiveRecord::StatementInvalid) do
+      Topic.pluck(topics: [:non_existent])
+    end
+  end
+
   def test_ids
     assert_equal Company.all.map(&:id).sort, Company.all.ids.sort
   end