diff --git a/src/Attribute/ConstrainActionEnum.php b/src/Attribute/ConstrainActionEnum.php
new file mode 100644
index 0000000..e4c58f8
--- /dev/null
+++ b/src/Attribute/ConstrainActionEnum.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Ulmus\Attribute;
+
+enum ConstrainActionEnum : string
+{
+    case Cascade = 'cascade';
+
+    case NoAction = 'noaction';
+
+    case Restrict = 'restrict';
+
+    case SetNull = 'setnull';
+}
diff --git a/src/Attribute/IndexTypeEnum.php b/src/Attribute/IndexTypeEnum.php
new file mode 100644
index 0000000..863f454
--- /dev/null
+++ b/src/Attribute/IndexTypeEnum.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace Ulmus\Attribute;
+
+enum IndexTypeEnum : string
+{
+    case Primary = 'primary';
+
+    case Index = 'index';
+
+    case Unique = 'unique';
+
+    case Spatial = 'spatial';
+
+    case Fulltext = 'fulltext';
+}
diff --git a/src/Attribute/Obj/Constrain.php b/src/Attribute/Obj/Constrain.php
new file mode 100644
index 0000000..c9e53e1
--- /dev/null
+++ b/src/Attribute/Obj/Constrain.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Ulmus\Attribute\Obj;
+
+use Ulmus\Attribute\Attribute;
+use Ulmus\Attribute\ConstrainActionEnum;
+use Ulmus\Attribute\IndexTypeEnum;
+
+#[\Attribute(\Attribute::TARGET_CLASS | \Attribute::IS_REPEATABLE)]
+class Constrain {
+    public function __construct(
+        public array $columns,
+        public null|IndexTypeEnum $type = null,
+        public null|string $name = null,
+        public null|array|string|\Stringable $foreignKey = null,
+        public null|array|string|\Stringable $references = null,
+        public ConstrainActionEnum $onDelete = ConstrainActionEnum::NoAction,
+        public ConstrainActionEnum $onUpdate = ConstrainActionEnum::NoAction,
+    ) {
+        $this->foreignKey = Attribute::handleArrayField($this->foreignKey, false);
+        $this->references = Attribute::handleArrayField($this->references, false);
+    }
+}
diff --git a/src/Attribute/Obj/Index.php b/src/Attribute/Obj/Index.php
new file mode 100644
index 0000000..4cd773f
--- /dev/null
+++ b/src/Attribute/Obj/Index.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Ulmus\Attribute\Obj;
+
+use Ulmus\Attribute\IndexTypeEnum;
+
+#[\Attribute(\Attribute::TARGET_CLASS | \Attribute::IS_REPEATABLE)]
+class Index {
+    public function __construct(
+        public string|array $column,
+        public IndexTypeEnum $type = IndexTypeEnum::Unique,
+        public null|string $name = null,
+    ) {}
+}
diff --git a/src/Attribute/Property/Field/ForeignKey.php b/src/Attribute/Property/Field/ForeignKey.php
index 252fdd4..11970a9 100644
--- a/src/Attribute/Property/Field/ForeignKey.php
+++ b/src/Attribute/Property/Field/ForeignKey.php
@@ -3,6 +3,7 @@
 namespace Ulmus\Attribute\Property\Field;
 
 use Ulmus\Attribute\Attribute;
+use Ulmus\Attribute\ConstrainActionEnum;
 
 /**
  * Since we need consistancy between the declaration of our ID and FK fields, it
@@ -10,17 +11,6 @@ use Ulmus\Attribute\Attribute;
  */
 #[\Attribute(\Attribute::TARGET_PROPERTY)]
 class ForeignKey extends PrimaryKey {
-
-    public const SET_NULL = "null";
-
-    public const SET_DEFAULT = "default";
-
-    public const RESTRICT = "restrict";
-
-    public const NO_ACTION = "noaction";
-
-    public const CASCADE = "cascade";
-
     public function __construct(
         public ? string $name = null,
         public ? string $type = 'bigint',
@@ -33,11 +23,10 @@ class ForeignKey extends PrimaryKey {
         public bool $nullable = false,
         public mixed $default = null,
         public bool $readonly = false,
-        public null|array|string|\Stringable $foreignKey = "",
-        public null|array|string|\Stringable $references = null,
-        public null|string $onDelete = self::NO_ACTION,
-        public null|string $onUpdate = self::NO_ACTION,
+        public null|string $relation = null,
+        public ConstrainActionEnum $onDelete = ConstrainActionEnum::NoAction,
+        public ConstrainActionEnum $onUpdate = ConstrainActionEnum::NoAction,
     ) {
-        $this->references = Attribute::handleArrayField($this->references, false);
+        #$this->references = Attribute::handleArrayField($this->references, false);
     }
 }
diff --git a/src/Attribute/Property/Index.php b/src/Attribute/Property/Index.php
index 70e6311..0d0fae9 100644
--- a/src/Attribute/Property/Index.php
+++ b/src/Attribute/Property/Index.php
@@ -2,20 +2,11 @@
 
 namespace Ulmus\Attribute\Property;
 
+use Ulmus\Attribute\IndexTypeEnum;
+
 #[\Attribute(\Attribute::TARGET_PROPERTY)]
 class Index {
-
-    public const TYPE_PRIMARY = 'primary';
-
-    public const TYPE_INDEX = 'index';
-
-    public const TYPE_UNIQUE = 'unique';
-
-    public const TYPE_SPATIAL = 'spatial';
-
-    public const TYPE_FULLTEXT = 'fulltext';
-
     public function __construct(
-        public string $type = self::TYPE_INDEX,
+        public IndexTypeEnum $type = IndexTypeEnum::Index,
     ) {}
-}
+}
\ No newline at end of file
diff --git a/src/Attribute/Property/Unique.php b/src/Attribute/Property/Unique.php
new file mode 100644
index 0000000..0889633
--- /dev/null
+++ b/src/Attribute/Property/Unique.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace Ulmus\Attribute\Property;
+
+use Ulmus\Attribute\IndexTypeEnum;
+
+#[\Attribute(\Attribute::TARGET_PROPERTY)]
+class Unique {
+
+    public function __construct(
+        public IndexTypeEnum $type = IndexTypeEnum::Unique,
+    ) {}
+}
diff --git a/src/EntityCollection.php b/src/EntityCollection.php
index e6d4914..152ebd5 100644
--- a/src/EntityCollection.php
+++ b/src/EntityCollection.php
@@ -8,7 +8,7 @@ class EntityCollection extends \ArrayObject implements \JsonSerializable {
 
     public ? string $entityClass = null;
 
-    public static function instance(array $data, null|string $entityClass) : self
+    public static function instance(array $data, null|string $entityClass = null) : self
     {
         $instance = new static($data);
         $instance->entityClass = $entityClass;