Verify foreign keys after mount when configured

Mirror Rails' fixture-loading FK check: when
ActiveRecord.verify_foreign_keys_for_fixtures is true (default since
Rails 8.0 load_defaults), call connection.check_all_foreign_keys_valid!
after the batch executes.

PG and SQLite raise on violations; MySQL is a no-op. Wrap any
StatementInvalid in a FixtureKit::Error with a hint that the cache may
be stale relative to the schema or fixture definitions — most likely
trigger is a developer regenerating fixtures against a different schema
than the one currently loaded.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ngan

lib/fixture_kit/coders/active_record_coder.rb

@@ -41,6 +41,8 @@ def mount(data)
             # This should be revisited when Rails 8.2 makes it public.
             connection.__send__(:execute_batch, statements, "FixtureKit Insert")
           end
+
+          verify_foreign_keys!(connection)
         end
       end
     end
@@ -93,6 +95,19 @@ def build_insert_sql(table_name, columns, rows, connection)
       "INSERT INTO #{quoted_table} (#{quoted_columns.join(", ")}) VALUES #{rows.join(", ")}"
     end
 
+    def verify_foreign_keys!(connection)
+      return unless ActiveRecord.verify_foreign_keys_for_fixtures
+
+      begin
+        connection.check_all_foreign_keys_valid!
+      rescue ActiveRecord::StatementInvalid => e
+        raise FixtureKit::Error,
+          "Foreign key violations found in cached fixture data. The cache may be " \
+          "stale relative to your current schema or fixture definitions. " \
+          "Original error:\n\n#{e.message}"
+      end
+    end
+
     def models_by_pool(data)
       seen = Set.new
 

spec/unit/coders/active_record_coder_spec.rb

@@ -146,6 +146,71 @@ def exercise_user_write_operations(suffix)
 
       coder.mount(records)
     end
+
+    context "when ActiveRecord.verify_foreign_keys_for_fixtures is true" do
+      around do |example|
+        previous = ActiveRecord.verify_foreign_keys_for_fixtures
+        ActiveRecord.verify_foreign_keys_for_fixtures = true
+        example.run
+      ensure
+        ActiveRecord.verify_foreign_keys_for_fixtures = previous
+      end
+
+      it "calls check_all_foreign_keys_valid! after the batch executes" do
+        records = { User => "INSERT INTO users (id, name) VALUES (1, 'Alice')" }
+        fake_connection = stub_fake_connection
+        stub_pool(User, fake_connection)
+
+        coder.mount(records)
+
+        expect(fake_connection).to have_received(:check_all_foreign_keys_valid!).once
+      end
+
+      it "wraps an FK violation in a FixtureKit::Error with a hint about stale cache" do
+        records = { User => "INSERT INTO users (id, name) VALUES (1, 'Alice')" }
+        fake_connection = stub_fake_connection
+        allow(fake_connection).to receive(:check_all_foreign_keys_valid!)
+          .and_raise(ActiveRecord::StatementInvalid, "Foreign key violations found: orders")
+        stub_pool(User, fake_connection)
+
+        expect { coder.mount(records) }.to raise_error(FixtureKit::Error, /cached fixture data.*stale.*Foreign key violations found: orders/m)
+      end
+    end
+
+    context "when ActiveRecord.verify_foreign_keys_for_fixtures is false" do
+      around do |example|
+        previous = ActiveRecord.verify_foreign_keys_for_fixtures
+        ActiveRecord.verify_foreign_keys_for_fixtures = false
+        example.run
+      ensure
+        ActiveRecord.verify_foreign_keys_for_fixtures = previous
+      end
+
+      it "does not call check_all_foreign_keys_valid!" do
+        records = { User => "INSERT INTO users (id, name) VALUES (1, 'Alice')" }
+        fake_connection = stub_fake_connection
+        stub_pool(User, fake_connection)
+
+        coder.mount(records)
+
+        expect(fake_connection).not_to have_received(:check_all_foreign_keys_valid!)
+      end
+    end
+
+    def stub_fake_connection
+      fake_connection = double("connection")
+      allow(fake_connection).to receive(:disable_referential_integrity).and_yield
+      allow(fake_connection).to receive(:execute_batch)
+      allow(fake_connection).to receive(:quote_table_name) { |name| %("#{name}") }
+      allow(fake_connection).to receive(:check_all_foreign_keys_valid!)
+      fake_connection
+    end
+
+    def stub_pool(model, connection)
+      pool = double("pool-for-#{model.name}")
+      allow(pool).to receive(:with_connection).and_yield(connection)
+      allow(model).to receive(:connection_pool).and_return(pool)
+    end
   end
 
   describe "sql.active_record payload name format assumptions" do