fix(database): saving nullable BelongsTo relations (#1584)

Author: brendt

packages/database/src/Mappers/SelectModelMapper.php

@@ -2,10 +2,8 @@
 
 namespace Tempest\Database\Mappers;
 
-use Exception;
 use Tempest\Database\BelongsTo;
 use Tempest\Database\Builder\ModelInspector;
-use Tempest\Database\Exceptions\ModelDidNotHavePrimaryColumn;
 use Tempest\Database\HasMany;
 use Tempest\Database\HasOne;
 use Tempest\Discovery\SkipDiscovery;
@@ -35,7 +33,31 @@ public function map(mixed $from, mixed $to): array
             ->map(fn (array $rows) => $this->normalizeFields($model, $rows))
             ->values();
 
-        return map($parsed->toArray())->collection()->to($to);
+        $objects = map($parsed->toArray())->collection()->to($to);
+
+        foreach ($objects as $i => $object) {
+            foreach ($model->getRelations() as $relation) {
+                // When a nullable BelongsTo relation wasn't loaded, we need to make sure to unset it if it has a default value.
+                // If we wouldn't do this, the default value would overwrite the "unloaded" value on the next time saving the model
+                if (! $relation instanceof BelongsTo) {
+                    continue;
+                }
+
+                if (! $relation->property->isNullable()) {
+                    continue;
+                }
+
+                if (! $relation->property->hasDefaultValue()) {
+                    continue;
+                }
+
+                if (! array_key_exists($relation->name, $parsed[$i] ?? [])) {
+                    $relation->property->unset($object);
+                }
+            }
+        }
+
+        return $objects;
     }
 
     private function normalizeFields(ModelInspector $model, array $rows): array

tests/Integration/Database/Builder/IsDatabaseModelTest.php

@@ -626,12 +626,38 @@ public function test_nullable_relations(): void
             CreateANullableTable::class,
         );
 
-        $a = ANullableModel::create();
+        $a = ANullableModel::create(
+            name: 'a',
+        );
 
         $a->load('b');
 
         $this->assertNull($a->b);
     }
+
+    public function test_nullable_relation_save(): void
+    {
+        $this->migrate(
+            CreateMigrationsTable::class,
+            CreateBNullableTable::class,
+            CreateANullableTable::class,
+        );
+
+        ANullableModel::create(
+            name: 'a',
+            b: BNullableModel::new(
+                name: 'b',
+            ),
+        );
+
+        $a = ANullableModel::select()->first();
+        $a->save();
+
+        $a = ANullableModel::select()->with('b')->first();
+
+        $this->assertNotNull($a->b);
+        $this->assertSame('b', $a->b->name);
+    }
 }
 
 final class Foo
@@ -987,6 +1013,7 @@ public function up(): QueryStatement
     {
         return new CreateTableStatement('a')
             ->primary()
+            ->string('name')
             ->belongsTo('a.b_id', 'b.id', nullable: true);
     }
 }
@@ -1009,6 +1036,8 @@ final class ANullableModel
     use IsDatabaseModel;
 
     public ?BNullableModel $b = null;
+
+    public string $name;
 }
 
 #[Table('b')]