sqlalchemy-to-ormar

A simple auto-translator from sqlalchemy ORM models to ormar models.

The ormar package is an async mini ORM for Python, with support for Postgres, MySQL, and SQLite.

To learn more about ormar:

• ormar github
• ormar documentation

Quickstart

from databases import Database
from sqlalchemy import (
    Column,
    ForeignKey,
    Integer,
    MetaData,
    String,
    create_engine,
    DECIMAL,
)
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import Session, relationship, sessionmaker

Base = declarative_base()
Database_URL = "sqlite:///test.db"
engine = create_engine(Database_URL, echo=True)


# given sqlalchemy models you already have
class User(Base):
    __tablename__ = "users"

    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    nickname = Column(String)
    salary = Column(DECIMAL)

    addresses = relationship(
        "Address", back_populates="user", cascade="all, delete, delete-orphan"
    )


class Address(Base):
    __tablename__ = "addresses"
    id = Column(Integer, primary_key=True)
    email_address = Column(String, nullable=False)
    user_id = Column(Integer, ForeignKey("users.id"))

    user = relationship("User", back_populates="addresses")


# instantiate new Databases instance
database = Database(Database_URL)
# note that you need new metadata instance as table names in ormar
# will remain the same and you cannot have two tables with same name in
# one metadata, note that we bind it to the same engine! 
# (or you can create new one with same url) 
metadata = MetaData(engine)

# use sqlalchemy-to-ormar (not normally imports should be at the top)
from sqlalchemy_to_ormar import ormar_model_str_repr, sqlalchemy_to_ormar

# convert sqlalchemy models to ormar
OrmarAddress = sqlalchemy_to_ormar(Address, database=database, metadata=metadata)
OrmarUser = sqlalchemy_to_ormar(User, database=database, metadata=metadata)

# you can print the ormar model
# or save it to file and you have proper model definition created for you

address_str = ormar_model_str_repr(OrmarAddress)

# now you can print it or save to file
print(address_str)
# will print:

# class OrmarAddress(ormar.Model):
# 
#     class Meta(ormar.ModelMeta):
#         metadata=metadata
#         database=database
#         tablename="addresses"
# 
#     id = ormar.Integer(autoincrement=True, primary_key=True)
#     email_address = ormar.String(max_length=255, nullable=False)
#     user = ormar.ForeignKey(to=OrmarUser, related_name="addresses", name=user_id, nullable=True)

# if you want to skip column aliases if they match field names use skip_names_if_match flag
user_model_str = ormar_model_str_repr(OrmarUser, skip_names_if_match=True)

# let's insert some sample data with sync sqlalchemy

Base.metadata.create_all(engine)
LocalSession = sessionmaker(bind=engine)
db: Session = LocalSession()

ed_user = User(name="ed", fullname="Ed Jones", nickname="edsnickname")
address = Address(email_address="[email protected]")
address2 = Address(email_address="[email protected]")
ed_user.addresses = [address, address2]

db.add(ed_user)
db.commit()

# and now we can query it asynchronously with ormar
async def test_ormar_queries(): 
    user = await OrmarUser.objects.select_related("addresses").get(name='ed')
    assert len(user.addresses) == 2
    assert user.nickname == 'edsnickname'
    assert user.fullname == 'Ed Jones'
    
    addresses = await OrmarAddress.objects.select_related('user').all(user__name='ed')
    assert len(addresses) == 2
    assert addresses[0].user.nickname == 'edsnickname'
    assert addresses[1].user.nickname == 'edsnickname'

# run async
import asyncio
asyncio.run(test_ormar_queries())

# drop db
Base.metadata.drop_all(engine)

Automap support

You can use sqlacodegen to generate sqlalchemy models out of existing database and then use sqlalchemy-to-ormar to translate it to ormar models.

Note that sqlalchemy has it's own automap feature, but out of experience it does not work well with complicated databases.

Supported fields

sqlalchemy-to-ormar supports following sqlalchemy field types:

• "integer": ormar.Integer,
• "small_integer": ormar.Integer,
• "big_integer": ormar.BigInteger,
• "string": ormar.String,
• "text": ormar.Text,
• "float": ormar.Float,
• "decimal": ormar.Decimal,
• "date": ormar.Date,
• "datetime": ormar.DateTime,
• "time": ormar.Time,
• "boolean": ormar.Boolean

Supported relations

sqlalchemy-to-ormar supports both ForeignKey as well as ManyToMany relations although like ormar itself it will create relation field on one side of the relation only and other side will be auto-populated with reversed side.

Known limitations

sqlalchemy to ormar right now does not support:

• composite (multi-column) primary keys and foreign keys (as ormar does not support them yet)
• cascade options from relationship are ignored, only the ones declared in sqlalchemy ForeignKey (ondelete, onupdate) are extracted
• ManyToMany fields names customization (as ormar does not support them yet)
• ManyToMany association table has to have primary key
• Model inheritance