✨ Add PydanticJSONB TypeDecorator for Automatic Pydantic Model Serialization in SQLModel

docs/advanced/index.md

@@ -1,10 +1,16 @@
 # Advanced User Guide
 
-The **Advanced User Guide** is gradually growing, you can already read about some advanced topics.
+The **Advanced User Guide** is gradually growing, you can already read about some advanced topics
 
-At some point it will include:
+Current topics include:
 
-* How to use `async` and `await` with the async session.
-* How to run migrations.
-* How to combine **SQLModel** models with SQLAlchemy.
+* [Working with Decimal Fields](decimal.md) - How to handle decimal numbers in SQLModel
+* [Working with UUID Fields](uuid.md) - How to use UUID fields in your models
+* [Storing Pydantic Models in JSONB Columns](pydantic-jsonb.md) - How to store and work with Pydantic models in JSONB columns
+
+Coming soon:
+
+* How to use `async` and `await` with the async session
+* How to run migrations
+* How to combine **SQLModel** models with SQLAlchemy
 * ...and more. 🤓

docs/advanced/pydantic-jsonb.md

@@ -0,0 +1,111 @@
+# Storing Pydantic Models in JSONB Columns
+
+You can store Pydantic models (and lists or dicts of them) in JSON or JSONB database columns using the `PydanticJSONB` utility.
+
+This is especially useful when:
+
+- You want to persist flexible, nested data structures in your models.
+- You prefer to avoid separate relational tables for structured fields like metadata, config, or address.
+- You want automatic serialization and deserialization using Pydantic.
+
+## Usage
+
+You can use it with SQLModel like this:
+
+```python
+from typing import Optional
+from pydantic import BaseModel
+from sqlmodel import SQLModel, Field, Column
+from sqlmodel.sql.sqltypes import PydanticJSONB
+
+class Address(BaseModel):
+    street: str
+    city: str
+
+class User(SQLModel, table=True):
+    id: Optional[int] = Field(default=None, primary_key=True)
+    name: str
+    address: Address = Field(sa_column=Column(PydanticJSONB(Address)))
+```
+
+This will store the `address` field as a `JSONB` column in PostgreSQL and automatically serialize/deserialize to and from the `Address` Pydantic model.
+
+If you're using a list or dict of models, `PydanticJSONB` supports that too:
+
+```python
+Field(sa_column=Column(PydanticJSONB(List[SomeModel])))
+Field(sa_column=Column(PydanticJSONB(Dict[str, SomeModel])))
+```
+
+## Create & Store Data
+
+Here's how to create and store data with Pydantic models in JSONB columns:
+
+```python
+from sqlmodel import Session, create_engine
+
+engine = create_engine("postgresql://user:password@localhost/db")
+
+# Insert a User with an Address
+with Session(engine) as session:
+    user = User(
+        name="John Doe",
+        address=Address(street="123 Main St", city="New York")
+    )
+    session.add(user)
+    session.commit()
+```
+
+## Retrieve & Use Data
+
+When you retrieve the data, it's automatically converted back to a Pydantic model:
+
+```python
+with Session(engine) as session:
+    user = session.query(User).first()
+    print(user.address.street)  # "123 Main St"
+    print(user.address.city)    # "New York"
+    print(type(user.address))   # <class '__main__.Address'>
+```
+
+Result:
+✅ No need for `Address(**user.address)` – it's already an `Address` instance!
+✅ Automatic conversion between JSONB and Pydantic models.
+
+This simplifies handling structured data in SQLModel, making JSONB storage seamless and ergonomic. 🚀
+
+## Requirements
+
+* PostgreSQL (for full `JSONB` support).
+* Pydantic v2.
+* SQLAlchemy 2.x.
+
+## Limitations
+
+### Nested Model Updates
+
+Currently, updating attributes inside a nested Pydantic model doesn't automatically trigger a database update. This is similar to how plain dictionaries work in SQLAlchemy. For example:
+
+```python
+# This won't trigger a database update
+row = select(...)  # some MyTable row
+row.data.x = 1
+db.add(row)  # no effect, change isn't detected
+```
+
+To update nested model attributes, you need to reassign the entire model:
+
+```python
+# Workaround: Create a new instance and reassign
+updated = ExtraData(**row.data.model_dump())
+updated.x = 1
+row.data = updated
+db.add(row)
+```
+
+This limitation will be addressed in a future update using `MutableDict` to enable change tracking for nested fields. The `MutableDict` implementation will emit change events when the contents of the dictionary are altered, including when values are added or removed.
+
+## Notes
+
+* Falls back to `JSON` if `JSONB` is not available.
+* Only tested with PostgreSQL at the moment.

mkdocs.yml

@@ -128,6 +128,7 @@ nav:
       - advanced/index.md
       - advanced/decimal.md
       - advanced/uuid.md
+      - advanced/pydantic-jsonb.md
   - Resources:
     - resources/index.md
     - help.md

sqlmodel/sql/sqltypes.py

@@ -1,16 +1,107 @@
-from typing import Any, cast
+from typing import (
+    Any,
+    Dict,
+    List,
+    Optional,
+    Type,
+    TypeVar,
+    Union,
+    cast,
+    get_args,
+    get_origin,
+)
 
-from sqlalchemy import types
+from pydantic import BaseModel
+from pydantic_core import to_jsonable_python
+from sqlalchemy import JSON, types
+from sqlalchemy.dialects.postgresql import JSONB  # for Postgres JSONB
 from sqlalchemy.engine.interfaces import Dialect
 
+BaseModelType = TypeVar("BaseModelType", bound=BaseModel)
+
+# Define a type alias for JSON-serializable values
+JSONValue = Union[Dict[str, Any], List[Any], str, int, float, bool, None]
+JSON_VARIANT = JSON().with_variant(JSONB, "postgresql")
+
 
 class AutoString(types.TypeDecorator):  # type: ignore
     impl = types.String
     cache_ok = True
     mysql_default_length = 255
 
-    def load_dialect_impl(self, dialect: Dialect) -> "types.TypeEngine[Any]":
+    def load_dialect_impl(self, dialect: Dialect) -> types.TypeEngine[Any]:
         impl = cast(types.String, self.impl)
         if impl.length is None and dialect.name == "mysql":
             return dialect.type_descriptor(types.String(self.mysql_default_length))
         return super().load_dialect_impl(dialect)
+
+
+class PydanticJSONB(types.TypeDecorator):  # type: ignore
+    """Custom type to automatically handle Pydantic model serialization."""
+
+    impl = JSON_VARIANT
+    cache_ok = True  # allow SQLAlchemy to cache results
+
+    def __init__(
+        self,
+        model_class: Union[
+            Type[BaseModelType],
+            Type[List[BaseModelType]],
+            Type[Dict[str, BaseModelType]],
+        ],
+        *args: Any,
+        **kwargs: Any,
+    ):
+        super().__init__(*args, **kwargs)
+        self.model_class = model_class  # Pydantic model class to use
+
+    def process_bind_param(self, value: Any, dialect: Any) -> JSONValue:  # noqa: ANN401, ARG002, ANN001
+        if value is None:
+            return None
+        if isinstance(value, BaseModel):
+            return value.model_dump(mode="json")
+        if isinstance(value, list):
+            return [
+                m.model_dump(mode="json")
+                if isinstance(m, BaseModel)
+                else to_jsonable_python(m)
+                for m in value
+            ]
+        if isinstance(value, dict):
+            return {
+                k: v.model_dump(mode="json")
+                if isinstance(v, BaseModel)
+                else to_jsonable_python(v)
+                for k, v in value.items()
+            }
+
+        # We know to_jsonable_python returns a JSON-serializable value, but mypy sees it as an Any type
+        return to_jsonable_python(value)  # type: ignore[no-any-return]
+
+    def process_result_value(
+        self, value: Any, dialect: Any
+    ) -> Optional[Union[BaseModelType, List[BaseModelType], Dict[str, BaseModelType]]]:  # noqa: ANN401, ARG002, ANN001
+        if value is None:
+            return None
+        if isinstance(value, dict):
+            # If model_class is a Dict type hint, handle key-value pairs
+            origin = get_origin(self.model_class)
+            if origin is dict:
+                model_class = get_args(self.model_class)[
+                    1
+                ]  # Get the value type (the model)
+                return {k: model_class.model_validate(v) for k, v in value.items()}
+            # Regular case: the whole dict represents a single model
+            return self.model_class.model_validate(value)  # type: ignore
+        if isinstance(value, list):
+            # If model_class is a List type hint
+            origin = get_origin(self.model_class)
+            if origin is list:
+                model_class = get_args(self.model_class)[0]
+                return [model_class.model_validate(v) for v in value]
+            # Fallback case (though this shouldn't happen given our __init__ types)
+            return [self.model_class.model_validate(v) for v in value]  # type: ignore
+
+        raise TypeError(
+            f"Unsupported type for PydanticJSONB from database: {type(value)}. Expected a dictionary or list."
+        )