[ENG-4003] Support DeclarativeBase in core

Add serializers and Var definitions for SQLAlchemy DeclarativeBase models.

reflex/model.py

@@ -2,8 +2,11 @@
 
 from __future__ import annotations
 
+import dataclasses
+import sys
 from collections import defaultdict
-from typing import Any, ClassVar, Optional, Type, Union
+from collections.abc import Mapping, MutableSet, Sequence
+from typing import Any, ClassVar, Optional, Type, TypeVar, Union
 
 import alembic.autogenerate
 import alembic.command
@@ -15,11 +18,14 @@ import alembic.util
 import sqlalchemy
 import sqlalchemy.exc
 import sqlalchemy.orm
+from sqlalchemy.orm import DeclarativeBase
 
 from reflex.base import Base
 from reflex.config import environment, get_config
 from reflex.utils import console
 from reflex.utils.compat import sqlmodel, sqlmodel_field_has_primary_key
+from reflex.utils.serializers import serializer
+from reflex.vars.object import LiteralObjectVar, ObjectVar
 
 
 def get_engine(url: str | None = None) -> sqlalchemy.engine.Engine:
@@ -435,3 +441,69 @@ def sqla_session(url: str | None = None) -> sqlalchemy.orm.Session:
         A database session.
     """
     return sqlalchemy.orm.Session(get_engine(url))
+
+
+class DeclarativeBaseVar(ObjectVar, python_types=DeclarativeBase):
+    """Var for a SQLAlchemy DeclarativeBase object."""
+
+
+@dataclasses.dataclass(
+    eq=False,
+    frozen=True,
+    **{"slots": True} if sys.version_info >= (3, 10) else {},
+)
+class LiteralDeclarativeBaseVar(LiteralObjectVar, DeclarativeBaseVar):
+    """Literal Var for a SQLAlchemy DeclarativeBase object."""
+
+    _var_value: DeclarativeBase | None = None
+
+
+T = TypeVar("T")
+K = TypeVar("K")
+V = TypeVar("V")
+
+
+@serializer
+def serialize_Sequence(s: Sequence[T] | MutableSet[T]) -> list[T]:
+    """Serialize a sequence or mutable set as a regular list.
+
+    Args:
+        s: The sequence or mutable set to serialize.
+
+    Returns:
+        The serialized list.
+    """
+    return list(s)
+
+
+@serializer
+def serialize_Mapping(m: Mapping[K, V]) -> dict[K, V]:
+    """Serialize a mapping as a regular dictionary.
+
+    Args:
+        m: The mapping to serialize.
+
+    Returns:
+        The serialized dictionary.
+    """
+    return dict(m)
+
+
+@serializer
+def serialize_DeclarativeBase(obj: DeclarativeBase) -> dict[str, str]:
+    """Serialize a SQLAlchemy DeclarativeBase object as a dictionary.
+
+    Args:
+        obj: The SQLAlchemy DeclarativeBase object to serialize.
+
+    Returns:
+        The serialized dictionary.
+    """
+    s = {}
+    for attr in sqlalchemy.inspect(type(obj)).all_orm_descriptors.keys():  # noqa: SIM118
+        try:
+            s[attr] = getattr(obj, attr)
+        except sqlalchemy.orm.exc.DetachedInstanceError:
+            # This happens when the relationship was never loaded and the session is closed.
+            continue
+    return s