Merge pull request #14757 from estsauver/14752

Fix behavior of select! to be consistent with select #14752

5 files changed, 19 insertions, 6 deletions

diff --git a/activerecord/lib/active_record/associations/preloader/association.rb b/activerecord/lib/active_record/associations/preloader/association.rb
index 69b65982b3..e2b1cef463 100644
--- a/activerecord/lib/active_record/associations/preloader/association.rb
+++ b/activerecord/lib/active_record/associations/preloader/association.rb
@@ -116,7 +116,7 @@ module ActiveRecord
           scope.where_values      = Array(values[:where])      + Array(preload_values[:where])
           scope.references_values = Array(values[:references]) + Array(preload_values[:references])
 
-          scope.select!   preload_values[:select] || values[:select] || table[Arel.star]
+          scope._select!   preload_values[:select] || values[:select] || table[Arel.star]
           scope.includes! preload_values[:includes] || values[:includes]
 
           if preload_values.key? :order
diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 21beed332f..9c666dcd3b 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -40,7 +40,7 @@ module ActiveRecord
     BLACKLISTED_ARRAY_METHODS = [
       :compact!, :flatten!, :reject!, :reverse!, :rotate!, :map!,
       :shuffle!, :slice!, :sort!, :sort_by!, :delete_if,
-      :keep_if, :pop, :shift, :delete_at, :compact
+      :keep_if, :pop, :shift, :delete_at, :compact, :select!
     ].to_set # :nodoc:
 
     delegate :to_xml, :to_yaml, :length, :collect, :map, :each, :all?, :include?, :to_ary, to: :to_a
diff --git a/activerecord/lib/active_record/relation/merger.rb b/activerecord/lib/active_record/relation/merger.rb
index be44fccad5..fcb28a18f6 100644
--- a/activerecord/lib/active_record/relation/merger.rb
+++ b/activerecord/lib/active_record/relation/merger.rb
@@ -30,6 +30,8 @@ module ActiveRecord
             else
               other.joins!(*v)
             end
+          elsif k == :select
+            other._select!(v)
           else
             other.send("#{k}!", v)
           end
@@ -62,7 +64,13 @@ module ActiveRecord
           # expensive), most of the time the value is going to be `nil` or `.blank?`, the only catch is that
           # `false.blank?` returns `true`, so there needs to be an extra check so that explicit `false` values
           # don't fall through the cracks.
-          relation.send("#{name}!", *value) unless value.nil? || (value.blank? && false != value)
+          unless value.nil? || (value.blank? && false != value)
+            if name == :select
+              relation._select!(*value)
+            else
+              relation.send("#{name}!", *value)
+            end
+          end
         end
 
         merge_multi_values
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 4287304945..5340fcb0b6 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -235,11 +235,11 @@ module ActiveRecord
         to_a.select { |*block_args| yield(*block_args) }
       else
         raise ArgumentError, 'Call this with at least one field' if fields.empty?
-        spawn.select!(*fields)
+        spawn._select!(*fields)
       end
     end
 
-    def select!(*fields) # :nodoc:
+    def _select!(*fields) # :nodoc:
       fields.flatten!
       fields.map! do |field|
         klass.attribute_alias?(field) ? klass.attribute_alias(field) : field
diff --git a/activerecord/test/cases/relation/mutation_test.rb b/activerecord/test/cases/relation/mutation_test.rb
index c81a3002d6..1da5c36e1c 100644
--- a/activerecord/test/cases/relation/mutation_test.rb
+++ b/activerecord/test/cases/relation/mutation_test.rb
@@ -24,13 +24,18 @@ module ActiveRecord
       @relation ||= Relation.new FakeKlass.new('posts'), Post.arel_table
     end
 
-    (Relation::MULTI_VALUE_METHODS - [:references, :extending, :order, :unscope]).each do |method|
+    (Relation::MULTI_VALUE_METHODS - [:references, :extending, :order, :unscope, :select]).each do |method|
       test "##{method}!" do
         assert relation.public_send("#{method}!", :foo).equal?(relation)
         assert_equal [:foo], relation.public_send("#{method}_values")
       end
     end
 
+    test "#_select!" do
+      assert relation.public_send("_select!", :foo).equal?(relation)
+      assert_equal [:foo], relation.public_send("select_values")
+    end
+
     test '#order!' do
       assert relation.order!('name ASC').equal?(relation)
       assert_equal ['name ASC'], relation.order_values