[ENG-3953] Support pydantic BaseModel (v1 and v2) as state var

Provide serializers and mutable proxy tracking for pydantic models directly.

reflex/state.py

@@ -39,6 +39,8 @@ from typing import (
     get_type_hints,
 )
 
+from pydantic import BaseModel as BaseModelV2
+from pydantic.v1 import BaseModel as BaseModelV1
 from sqlalchemy.orm import DeclarativeBase
 from typing_extensions import Self
 
@@ -3520,7 +3522,15 @@ class MutableProxy(wrapt.ObjectProxy):
         pydantic.BaseModel.__dict__
     )
 
-    __mutable_types__ = (list, dict, set, Base, DeclarativeBase)
+    __mutable_types__ = (
+        list,
+        dict,
+        set,
+        Base,
+        DeclarativeBase,
+        BaseModelV2,
+        BaseModelV1,
+    )
 
     def __init__(self, wrapped: Any, state: BaseState, field_name: str):
         """Create a proxy for a mutable object that tracks changes.

reflex/utils/serializers.py

@@ -24,6 +24,9 @@ from typing import (
     overload,
 )
 
+from pydantic import BaseModel as BaseModelV2
+from pydantic.v1 import BaseModel as BaseModelV1
+
 from reflex.base import Base
 from reflex.constants.colors import Color, format_color
 from reflex.utils import types
@@ -266,6 +269,32 @@ def serialize_base(value: Base) -> dict:
     return {k: v for k, v in value.dict().items() if not callable(v)}
 
 
+@serializer(to=dict)
+def serialize_base_model_v1(model: BaseModelV1) -> dict:
+    """Serialize a pydantic v1 BaseModel instance.
+
+    Args:
+        model: The BaseModel to serialize.
+
+    Returns:
+        The serialized BaseModel.
+    """
+    return model.dict()
+
+
+@serializer(to=dict)
+def serialize_base_model_v2(model: BaseModelV2) -> dict:
+    """Serialize a pydantic v2 BaseModel instance.
+
+    Args:
+        model: The BaseModel to serialize.
+
+    Returns:
+        The serialized BaseModel.
+    """
+    return model.model_dump()
+
+
 @serializer
 def serialize_set(value: Set) -> list:
     """Serialize a set to a JSON serializable list.

tests/units/test_state.py

@@ -16,6 +16,8 @@ from unittest.mock import AsyncMock, Mock
 import pytest
 import pytest_asyncio
 from plotly.graph_objects import Figure
+from pydantic import BaseModel as BaseModelV2
+from pydantic.v1 import BaseModel as BaseModelV1
 
 import reflex as rx
 import reflex.config
@@ -3411,3 +3413,34 @@ def test_typed_state() -> None:
         field: rx.Field[str] = rx.field("")
 
     _ = TypedState(field="str")
+
+
+class ModelV1(BaseModelV1):
+    """A pydantic BaseModel v1."""
+
+    foo: str = "bar"
+
+
+class ModelV2(BaseModelV2):
+    """A pydantic BaseModel v2."""
+
+    foo: str = "bar"
+
+
+class PydanticState(rx.State):
+    """A state with pydantic BaseModel vars."""
+
+    v1: ModelV1 = ModelV1()
+    v2: ModelV2 = ModelV2()
+
+
+def test_pydantic_base_models():
+    """Test that pydantic BaseModel v1 and v2 can be used as state vars with dep tracking."""
+    state = PydanticState()
+    assert isinstance(state.v1, MutableProxy)
+    state.v1.foo = "baz"
+    assert "v1" in state.dirty_vars
+
+    assert isinstance(state.v2, MutableProxy)
+    state.v2.foo = "baz"
+    assert "v2" in state.dirty_vars