docarray · samsja · Jan 30, 2023 · Jan 24, 2023 · Jan 24, 2023 · Jan 24, 2023
diff --git a/docarray/array/abstract_array.py b/docarray/array/abstract_array.py
@@ -1,5 +1,15 @@
 from abc import abstractmethod
-from typing import TYPE_CHECKING, Any, Generic, List, Sequence, Type, TypeVar, Union
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Dict,
+    Generic,
+    List,
+    Sequence,
+    Type,
+    TypeVar,
+    Union,
+)
 
 from docarray.base_document import BaseDocument
 from docarray.display.document_array_summary import DocumentArraySummary
@@ -17,6 +27,7 @@
 class AnyDocumentArray(Sequence[BaseDocument], Generic[T_doc], AbstractType):
     document_type: Type[BaseDocument]
     tensor_type: Type['AbstractTensor'] = NdArray
+    __typed_da__: Dict[Type[BaseDocument], Type] = {}
 
     def __repr__(self):
         return f'<{self.__class__.__name__} (length={len(self)})>'
@@ -27,28 +38,31 @@ def __class_getitem__(cls, item: Type[BaseDocument]):
                 f'{cls.__name__}[item] item should be a Document not a {item} '
             )
 
-        class _DocumentArrayTyped(cls):  # type: ignore
-            document_type: Type[BaseDocument] = item
+        if item not in cls.__typed_da__:
 
-        for field in _DocumentArrayTyped.document_type.__fields__.keys():
+            class _DocumentArrayTyped(cls):  # type: ignore
+                document_type: Type[BaseDocument] = item
 
-            def _property_generator(val: str):
-                def _getter(self):
-                    return self._get_array_attribute(val)
+            for field in _DocumentArrayTyped.document_type.__fields__.keys():
 
-                def _setter(self, value):
-                    self._set_array_attribute(val, value)
+                def _property_generator(val: str):
+                    def _getter(self):
+                        return self._get_array_attribute(val)
 
-                # need docstring for the property
-                return property(fget=_getter, fset=_setter)
+                    def _setter(self, value):
+                        self._set_array_attribute(val, value)
 
-            setattr(_DocumentArrayTyped, field, _property_generator(field))
-            # this generates property on the fly based on the schema of the item
+                    # need docstring for the property
+                    return property(fget=_getter, fset=_setter)
 
-        _DocumentArrayTyped.__name__ = f'{cls.__name__}[{item.__name__}]'
-        _DocumentArrayTyped.__qualname__ = f'{cls.__name__}[{item.__name__}]'
+                setattr(_DocumentArrayTyped, field, _property_generator(field))
+                # this generates property on the fly based on the schema of the item
 
-        return _DocumentArrayTyped
+            _DocumentArrayTyped.__name__ = f'{cls.__name__}[{item.__name__}]'
+            _DocumentArrayTyped.__qualname__ = f'{cls.__name__}[{item.__name__}]'
+            cls.__typed_da__[item] = _DocumentArrayTyped
+
+        return cls.__typed_da__[item]
 
     @abstractmethod
     def _get_array_attribute(

diff --git a/docarray/array/array.py b/docarray/array/array.py
@@ -1,6 +1,16 @@
 from contextlib import contextmanager
 from functools import wraps
-from typing import TYPE_CHECKING, Any, Callable, Iterable, List, Type, TypeVar, Union
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Callable,
+    Dict,
+    Iterable,
+    List,
+    Type,
+    TypeVar,
+    Union,
+)
 
 from typing_inspect import is_union_type
 
@@ -73,6 +83,7 @@ class Image(BaseDocument):
     """
 
     document_type: Type[BaseDocument] = AnyDocument
+    __typed_da__: Dict[Type[BaseDocument], Type] = {}
 
     def __init__(
         self,

diff --git a/docarray/array/array_stacked.py b/docarray/array/array_stacked.py
@@ -56,6 +56,7 @@ class DocumentArrayStacked(AnyDocumentArray):
 
     document_type: Type[BaseDocument] = AnyDocument
     _docs: DocumentArray
+    __typed_da__: Dict[Type[BaseDocument], Type] = {}
 
     def __init__(
         self: T,

diff --git a/tests/units/typing/da/__init__.py b/tests/units/typing/da/__init__.py
diff --git a/tests/units/typing/da/test_relations.py b/tests/units/typing/da/test_relations.py
@@ -0,0 +1,33 @@
+from docarray import BaseDocument, DocumentArray
+
+
+def test_instance_and_equivalence():
+    class MyDoc(BaseDocument):
+        text: str
+
+    docs = DocumentArray[MyDoc]([MyDoc(text='hello')])
+
+    assert issubclass(DocumentArray[MyDoc], DocumentArray[MyDoc])
+    assert issubclass(docs.__class__, DocumentArray[MyDoc])
+
+    assert isinstance(docs, DocumentArray[MyDoc])
+
+
+def test_subclassing():
+    class MyDoc(BaseDocument):
+        text: str
+
+    class MyDocArray(DocumentArray[MyDoc]):
+        pass
+
+    docs = MyDocArray([MyDoc(text='hello')])
+
+    assert issubclass(MyDocArray, DocumentArray[MyDoc])
+    assert issubclass(docs.__class__, DocumentArray[MyDoc])
+
+    assert isinstance(docs, MyDocArray)
+    assert isinstance(docs, DocumentArray[MyDoc])
+
+    assert issubclass(MyDoc, BaseDocument)
+    assert not issubclass(DocumentArray[MyDoc], DocumentArray[BaseDocument])
+    assert not issubclass(MyDocArray, DocumentArray[BaseDocument])