Allow ActiveRecord::QueryMethods#pluck to accept hash args with symbol & string values

activerecord/CHANGELOG.md

@@ -1,3 +1,12 @@
+*   Allow `ActiveRecord::Base#pluck` to accept hash arguments with symbol and string values.
+
+    ```ruby
+    Post.joins(:comments).pluck(:id, comments: :id)
+    Post.joins(:comments).pluck("id", "comments" => "id")
+    ```
+
+    *Joshua Young*
+
 *   Strict loading using `:n_plus_one_only` does not eagerly load child associations.
 
     With this change, child associations are no longer eagerly loaded, to

activerecord/lib/active_record/relation/calculations.rb

@@ -275,10 +275,14 @@ 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])
+    #   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]]
     #
+    #   Comment.joins(:person).pluck(:id, person: [:id, :name])
+    #   # SELECT comments.id, people.id, people.name FROM comments INNER JOIN people on comments.person_id = people.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']

activerecord/lib/active_record/relation/query_methods.rb

@@ -2110,14 +2110,14 @@ 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)
-            arel_columns_from_hash(field)
+            arel_columns_from_hash(field, for_select: true)
           else
             field
           end
         end
       end
 
-      def arel_columns_from_hash(fields)
+      def arel_columns_from_hash(fields, for_select: false)
         fields.flat_map do |key, columns_aliases|
           case columns_aliases
           when Hash
@@ -2126,22 +2126,30 @@ def arel_columns_from_hash(fields)
                 references = PredicateBuilder.references({ key.to_s => fields[key] })
                 self.references_values |= references unless references.empty?
               end
-              arel_column("#{key}.#{column}") do
-                predicate_builder.resolve_arel_attribute(key.to_s, column)
-              end.as(column_alias.to_s)
+              build_arel_attribute(key.to_s, column.to_s).as(column_alias.to_s)
             end
           when Array
             columns_aliases.map do |column|
               arel_column("#{key}.#{column}", &:itself)
             end
           when String, Symbol
-            arel_column(key.to_s) do
-              predicate_builder.resolve_arel_attribute(klass.table_name, key.to_s)
-            end.as(columns_aliases.to_s)
+            if for_select
+              arel_column(key.to_s) do
+                predicate_builder.resolve_arel_attribute(klass.table_name, key.to_s)
+              end.as(columns_aliases.to_s)
+            else
+              build_arel_attribute(key.to_s, columns_aliases.to_s)
+            end
           end
         end
       end
 
+      def build_arel_attribute(table_name, column_name)
+        arel_column("#{table_name}.#{column_name}") do
+          predicate_builder.resolve_arel_attribute(table_name.to_s, column_name)
+        end
+      end
+
       STRUCTURAL_VALUE_METHODS = (
         Relation::VALUE_METHODS -
         [:extending, :where, :having, :unscope, :references, :annotate, :optimizer_hints]

activerecord/test/cases/calculations_test.rb

@@ -958,7 +958,10 @@ def test_pluck_with_hash_argument
       [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)
+    assert_equal expected, Topic.order(:id).limit(3).pluck("id", "topics" => "title")
     assert_equal expected, Topic.order(:id).limit(3).pluck(:id, topics: [:title])
+    assert_equal expected, Topic.order(:id).limit(3).pluck("id", "topics" => ["title"])
   end
 
   def test_pluck_with_hash_argument_with_multiple_tables
@@ -967,6 +970,8 @@ def test_pluck_with_hash_argument_with_multiple_tables
       [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(:id, comments: [:id, :body])
+    assert_equal expected, Post.joins(:comments).order(posts: { id: :asc }, comments: { id: :asc }).limit(3).pluck(posts: :id, comments: [:id, :body])
     assert_equal expected, Post.joins(:comments).order(posts: { id: :asc }, comments: { id: :asc }).limit(3).pluck(posts: [:id], comments: [:id, :body])
   end