disallow mutating a relation once loaded

3 files changed, 50 insertions, 18 deletions

diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
index 9b88bb8178..858b667e22 100644
--- a/activerecord/lib/active_record/errors.rb
+++ b/activerecord/lib/active_record/errors.rb
@@ -196,4 +196,7 @@ module ActiveRecord
       "Unknown primary key for table #{model.table_name} in model #{model}."
     end
   end
+
+  class ImmutableRelation < ActiveRecordError
+  end
 end
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 529ddb5e31..e394acfaf2 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -7,34 +7,36 @@ module ActiveRecord
 
     Relation::MULTI_VALUE_METHODS.each do |name|
       class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}_values            # def select_values
-          @values[:#{name}] || []     #   @values[:select] || []
-        end                           # end
-                                      #
-        def #{name}_values=(values)   # def select_values=(values)
-          @values[:#{name}] = values  #   @values[:select] = values
-        end                           # end
+        def #{name}_values                   # def select_values
+          @values[:#{name}] || []            #   @values[:select] || []
+        end                                  # end
+                                             #
+        def #{name}_values=(values)          # def select_values=(values)
+          raise ImmutableRelation if @loaded #   raise ImmutableRelation if @loaded
+          @values[:#{name}] = values         #   @values[:select] = values
+        end                                  # end
       CODE
     end
 
     (Relation::SINGLE_VALUE_METHODS - [:create_with]).each do |name|
       class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}_value             # def readonly_value
-          @values[:#{name}]           #   @values[:readonly]
-        end                           # end
-                                      #
-        def #{name}_value=(value)     # def readonly_value=(value)
-          @values[:#{name}] = value   #   @values[:readonly] = value
-        end                           # end
+        def #{name}_value                    # def readonly_value
+          @values[:#{name}]                  #   @values[:readonly]
+        end                                  # end
       CODE
     end
 
-    def create_with_value
-      @values[:create_with] || {}
+    Relation::SINGLE_VALUE_METHODS.each do |name|
+      class_eval <<-CODE, __FILE__, __LINE__ + 1
+        def #{name}_value=(value)            # def readonly_value=(value)
+          raise ImmutableRelation if @loaded #   raise ImmutableRelation if @loaded
+          @values[:#{name}] = value          #   @values[:readonly] = value
+        end                                  # end
+      CODE
     end
 
-    def create_with_value=(value)
-      @values[:create_with] = value
+    def create_with_value
+      @values[:create_with] || {}
     end
 
     alias extensions extending_values
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 6c5bee7382..8544d36aa8 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -1284,4 +1284,31 @@ class RelationTest < ActiveRecord::TestCase
       Post.scoped.find_by!("1 = 0")
     end
   end
+
+  test "loaded relations cannot be mutated by multi value methods" do
+    relation = Post.scoped
+    relation.to_a
+
+    assert_raises(ActiveRecord::ImmutableRelation) do
+      relation.where! 'foo'
+    end
+  end
+
+  test "loaded relations cannot be mutated by single value methods" do
+    relation = Post.scoped
+    relation.to_a
+
+    assert_raises(ActiveRecord::ImmutableRelation) do
+      relation.limit! 5
+    end
+  end
+
+  test "loaded relations cannot be mutated by merge!" do
+    relation = Post.scoped
+    relation.to_a
+
+    assert_raises(ActiveRecord::ImmutableRelation) do
+      relation.merge! where: 'foo'
+    end
+  end
 end