strawberry-sqlalchemy-mapper

Strawberry-sqlalchemy-mapper is the simplest way to implement autogenerated strawberry types for columns and relationships in SQLAlchemy models.

• Instead of manually listing every column and relationship in a SQLAlchemy model, strawberry-sqlalchemy-mapper lets you decorate a class declaration and it will automatically generate the necessary strawberry fields for all columns and relationships (subject to the limitations below) in the given model.

• Native support for most of SQLAlchemy's most common types.

• Extensible to arbitrary custom SQLAlchemy types.

• Automatic batching of queries, avoiding N+1 queries when getting relationships

• Support for SQLAlchemy >=1.4.x

• Lightweight and fast.

Getting Started

strawberry-sqlalchemy-mapper is available on PyPi

pip install strawberry-sqlalchemy-mapper

First, define your sqlalchemy model:

# models.py
from sqlalchemy import Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Employee(Base):
    __tablename__ = 'employee'
    id = Column(UUID, primary_key=True)
    name = Column(String, nullable=False)
    password_hash = Column(String, nullable=False)
    department_id = Column(UUID, ForeignKey('department.id'))
    department = relationship('Department', back_populates='employees')

class Department(Base):
    __tablename__ = "department"
    id = Column(UUID, primary_key=True)
    name = Column(String, nullable=False)
    employees = relationship('Employee', back_populates='department')

Next, decorate a type with strawberry_sqlalchemy_mapper.type() to register it as a strawberry type for the given SQLAlchemy model. This will automatically add fields for the model's columns, relationships, association proxies, and hybrid properties. For example:

# elsewhere
# ...
from strawberry_sqlalchemy_mapper import StrawberrySQLAlchemyMapper

strawberry_sqlalchemy_mapper = StrawberrySQLAlchemyMapper()
@strawberry_sqlalchemy_mapper.type(models.Employee)
class Employee:
    __exclude__ = ["password_hash"]


@strawberry_sqlalchemy_mapper.type(models.Department)
class Department:
    pass

@strawberry.type
class Query:
    @strawberry.field
    def departments(self):
        return db.session.scalars(select(models.Department)).all()


# context is expected to have an instance of StrawberrySQLAlchemyLoader
class CustomGraphQLView(GraphQLView):
    def get_context(self):
        return {
            "sqlalchemy_loader": StrawberrySQLAlchemyLoader(bind=YOUR_SESSION),
        }

# call finalize() before using the schema:
# (note that models that are related to models that are in the schema
# are automatically mapped at this stage -- e.g., Department is mapped
# because employee.department is a relationshp to Department)
strawberry_sqlalchemy_mapper.finalize()
# only needed if you have polymorphic types
additional_types = list(strawberry_sqlalchemy_mapper.mapped_types.values())
schema = strawberry.Schema(
    query=Query,
    mutation=Mutation,
    extensions=extensions,
    types=additional_types,
)

# You can now query, e.g.:
"""
query {
    departments {
        id
        name
        employees {
            edge {
                node {
                    id
                    name
                    department {
                        # Just an example of nested relationships
                        id
                        name
                    }
                }
            }
        }
    }
}
"""

Limitations

SQLAlchemy Models -> Strawberry Types and Interfaces are expected to have a consistent (customizable) naming convention. These can be configured by passing model_to_type_name and model_to_interface_name when constructing the mapper.

Natively supports the following SQLAlchemy types:

Integer: int,
Float: float,
BigInteger: int,
Numeric: Decimal,
DateTime: datetime,
Date: date,
Time: time,
String: str,
Text: str,
Boolean: bool,
Unicode: str,
UnicodeText: str,
SmallInteger: int,
SQLAlchemyUUID: uuid.UUID,
VARCHAR: str,
ARRAY[T]: List[T] # PostgreSQL array
Enum: (the Python enum it is mapped to, which should be @strawberry.enum-decorated)

Additional types can be supported by passing extra_sqlalchemy_type_to_strawberry_type_map, although support for TypeDecorator types is untested.

Association proxies are expected to be of the form association_proxy('relationship1', 'relationship2'), i.e., both properties are expected to be relationships.

Roots of polymorphic hierarchies are supported, but are also expected to be registered via strawberry_sqlalchemy_mapper.interface(), and its concrete type and its descendants are expected to inherit from the interface:

class Book(Model):
    id = Column(UUID, primary_key=True)

class Novel(Book):
    pass

class ShortStory(Book):
    pass


# in another file
strawberry_sqlalchemy_mapper = StrawberrySQLAlchemyMapper()

@strawberry_sqlalchemy_mapper.interface(models.Book)
class BookInterface:
    pass

@strawberry_sqlalchemy_mapper.type(models.Book)
class Book:
    pass

@strawberry_sqlalchemy_mapper.type(models.Novel)
class Novel:
    pass

@strawberry_sqlalchemy_mapper.type(models.ShortStory)
class ShortStory:
    pass

Contributing

We encourage you to contribute to strawberry-sqlalchemy-mapper! Any contributions you make are greatly appreciated.

If you have a suggestion that would make this better, please fork the repo and create a pull request. Don't forget to give the project a star! Thanks again!

1. Fork the Project
2. Create your Feature Branch (git checkout -b feature)
3. Commit your Changes (git commit -m 'Add some feature')
4. Push to the Branch (git push origin feature)
5. Open a Pull Request

Prerequisites

This project uses pre-commit_, please make sure to install it before making any changes::

pip install pre-commit
cd strawberry-sqlalchemy-mapper
pre-commit install

It is a good idea to update the hooks to the latest version::

pre-commit autoupdate

Don't forget to tell your contributors to also install and use pre-commit.

Installation

pip install -r requirements.txt

Test

pytest

⚖️ LICENSE

MIT © strawberry-sqlalchemy-mapper