fix: support generic dataclass (#525)

dataclasses_json/core.py

@@ -24,7 +24,8 @@
                                     _get_type_arg_param,
                                     _get_type_args, _is_counter,
                                     _NO_ARGS,
-                                    _issubclass_safe, _is_tuple)
+                                    _issubclass_safe, _is_tuple,
+                                    _is_generic_dataclass)
 
 Json = Union[dict, list, str, int, float, bool, None]
 
@@ -269,8 +270,9 @@ def _is_supported_generic(type_):
         return False
     not_str = not _issubclass_safe(type_, str)
     is_enum = _issubclass_safe(type_, Enum)
+    is_generic_dataclass = _is_generic_dataclass(type_)
     return (not_str and _is_collection(type_)) or _is_optional(
-        type_) or is_union_type(type_) or is_enum
+        type_) or is_union_type(type_) or is_enum or is_generic_dataclass
 
 
 def _decode_generic(type_, value, infer_missing):
@@ -308,6 +310,9 @@ def _decode_generic(type_, value, infer_missing):
         except (TypeError, AttributeError):
             pass
         res = materialize_type(xs)
+    elif _is_generic_dataclass(type_):
+        origin = _get_type_origin(type_)
+        res = _decode_dataclass(origin, value, infer_missing)
     else:  # Optional or Union
         _args = _get_type_args(type_)
         if _args is _NO_ARGS:

dataclasses_json/utils.py

@@ -2,6 +2,7 @@
 import sys
 from datetime import datetime, timezone
 from collections import Counter
+from dataclasses import is_dataclass  # type: ignore
 from typing import (Collection, Mapping, Optional, TypeVar, Any, Type, Tuple,
                     Union, cast)
 
@@ -164,6 +165,10 @@ def _is_nonstr_collection(type_):
             and not _issubclass_safe(type_, str))
 
 
+def _is_generic_dataclass(type_):
+    return is_dataclass(_get_type_origin(type_))
+
+
 def _timestamp_to_dt_aware(timestamp: float):
     tz = datetime.now(timezone.utc).astimezone().tzinfo
     dt = datetime.fromtimestamp(timestamp, tz=tz)

tests/test_generic_dataclass.py

@@ -0,0 +1,83 @@
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Generic, TypeVar
+
+import pytest
+
+from dataclasses_json import dataclass_json
+
+S = TypeVar("S")
+T = TypeVar("T")
+
+
+@dataclass_json
+@dataclass
+class Bar:
+    value: int
+
+
+@dataclass_json
+@dataclass
+class Foo(Generic[T]):
+    bar: T
+
+
+@dataclass_json
+@dataclass
+class Baz(Generic[T]):
+    foo: Foo[T]
+
+
+@pytest.mark.parametrize(
+    "instance_of_t, decodes_successfully",
+    [
+        pytest.param(1, True, id="literal"),
+        pytest.param([1], True, id="literal_list"),
+        pytest.param({"a": 1}, True, id="map_of_literal"),
+        pytest.param(datetime(2021, 1, 1), False, id="extended_type"),
+        pytest.param(Bar(1), False, id="object"),
+    ]
+)
+def test_dataclass_with_generic_dataclass_field(instance_of_t, decodes_successfully):
+    foo = Foo(bar=instance_of_t)
+    baz = Baz(foo=foo)
+    decoded = Baz[type(instance_of_t)].from_json(baz.to_json())
+    assert decoded.foo == Foo.from_json(foo.to_json())
+    if decodes_successfully:
+        assert decoded == baz
+    else:
+        assert decoded != baz
+
+
+@dataclass_json
+@dataclass
+class Foo2(Generic[T, S]):
+    bar1: T
+    bar2: S
+
+
+@dataclass_json
+@dataclass
+class Baz2(Generic[T, S]):
+    foo2: Foo2[T, S]
+
+
+@pytest.mark.parametrize(
+    "instance_of_t, decodes_successfully",
+    [
+        pytest.param(1, True, id="literal"),
+        pytest.param([1], True, id="literal_list"),
+        pytest.param({"a": 1}, True, id="map_of_literal"),
+        pytest.param(datetime(2021, 1, 1), False, id="extended_type"),
+        pytest.param(Bar(1), False, id="object"),
+    ]
+)
+def test_dataclass_with_multiple_generic_dataclass_fields(instance_of_t, decodes_successfully):
+    foo2 = Foo2(bar1=instance_of_t, bar2=instance_of_t)
+    baz = Baz2(foo2=foo2)
+    decoded = Baz2[type(instance_of_t), type(instance_of_t)].from_json(baz.to_json())
+    assert decoded.foo2 == Foo2.from_json(foo2.to_json())
+    if decodes_successfully:
+        assert decoded == baz
+    else:
+        assert decoded != baz