From 59c3ed1b3f90db197000e3867f255781a02412e7 Mon Sep 17 00:00:00 2001
From: George Claghorn <george@basecamp.com>
Date: Mon, 30 Jul 2018 08:40:48 -0400
Subject: MySQL: Raise ActiveRecord::InvalidForeignKey for foreign-key
 constraint violations on delete

---
 .../connection_adapters/abstract_mysql_adapter.rb   |  3 ++-
 activerecord/lib/active_record/errors.rb            |  3 ++-
 activerecord/test/cases/adapter_test.rb             | 21 ++++++++++++++++-----
 3 files changed, 20 insertions(+), 7 deletions(-)

(limited to 'activerecord')

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 284b38ed7b..9de8242a58 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -619,6 +619,7 @@ module ActiveRecord
         ER_DUP_ENTRY            = 1062
         ER_NOT_NULL_VIOLATION   = 1048
         ER_DO_NOT_HAVE_DEFAULT  = 1364
+        ER_ROW_IS_REFERENCED_2  = 1451
         ER_NO_REFERENCED_ROW_2  = 1452
         ER_DATA_TOO_LONG        = 1406
         ER_OUT_OF_RANGE         = 1264
@@ -633,7 +634,7 @@ module ActiveRecord
           case error_number(exception)
           when ER_DUP_ENTRY
             RecordNotUnique.new(message)
-          when ER_NO_REFERENCED_ROW_2
+          when ER_ROW_IS_REFERENCED_2, ER_NO_REFERENCED_ROW_2
             InvalidForeignKey.new(message)
           when ER_CANNOT_ADD_FOREIGN
             mismatched_foreign_key(message)
diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
index c2a180c939..f61bc7b9e8 100644
--- a/activerecord/lib/active_record/errors.rb
+++ b/activerecord/lib/active_record/errors.rb
@@ -111,7 +111,8 @@ module ActiveRecord
   class RecordNotUnique < WrappedDatabaseException
   end
 
-  # Raised when a record cannot be inserted or updated because it references a non-existent record.
+  # Raised when a record cannot be inserted or updated because it references a non-existent record,
+  # or when a record cannot be deleted because a parent record references it.
   class InvalidForeignKey < WrappedDatabaseException
   end
 
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 79642f5871..59b99351d1 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -304,6 +304,8 @@ module ActiveRecord
   class AdapterForeignKeyTest < ActiveRecord::TestCase
     self.use_transactional_tests = false
 
+    fixtures :fk_test_has_pk
+
     def setup
       @connection = ActiveRecord::Base.connection
     end
@@ -322,7 +324,7 @@ module ActiveRecord
       assert_not_nil error.cause
     end
 
-    def test_foreign_key_violations_are_translated_to_specific_exception
+    def test_foreign_key_violations_on_insert_are_translated_to_specific_exception
       error = assert_raises(ActiveRecord::InvalidForeignKey) do
         insert_into_fk_test_has_fk
       end
@@ -330,6 +332,16 @@ module ActiveRecord
       assert_not_nil error.cause
     end
 
+    def test_foreign_key_violations_on_delete_are_translated_to_specific_exception
+      insert_into_fk_test_has_fk fk_id: 1
+
+      error = assert_raises(ActiveRecord::InvalidForeignKey) do
+        @connection.execute "DELETE FROM fk_test_has_pk WHERE pk_id = 1"
+      end
+
+      assert_not_nil error.cause
+    end
+
     def test_disable_referential_integrity
       assert_nothing_raised do
         @connection.disable_referential_integrity do
@@ -342,14 +354,13 @@ module ActiveRecord
     end
 
     private
-
-      def insert_into_fk_test_has_fk
+      def insert_into_fk_test_has_fk(fk_id: 0)
         # Oracle adapter uses prefetched primary key values from sequence and passes them to connection adapter insert method
         if @connection.prefetch_primary_key?
           id_value = @connection.next_sequence_value(@connection.default_sequence_name("fk_test_has_fk", "id"))
-          @connection.execute "INSERT INTO fk_test_has_fk (id,fk_id) VALUES (#{id_value},0)"
+          @connection.execute "INSERT INTO fk_test_has_fk (id,fk_id) VALUES (#{id_value},#{fk_id})"
         else
-          @connection.execute "INSERT INTO fk_test_has_fk (fk_id) VALUES (0)"
+          @connection.execute "INSERT INTO fk_test_has_fk (fk_id) VALUES (#{fk_id})"
         end
       end
   end
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