Add example for dataclass with relationship #11639
Conversation
|
Hi, Thanks for the effort, but I would rather implement the Or maybe this could be merged in the meantime and updated later to make use of the no-value thing once it's merged? |
|
Yes, I was not expecting you to merge this as it. It was mainly to help you have an easy example to setup for the development as this discussion #9410 was marked as PR with tests welcome. But writing that I figure that you were probably expecting an implementation for |
This comment was marked as spam.
This comment was marked as spam.
Sorry, something went wrong.
zzzeek
left a comment
zzzeek
left a comment
There was a problem hiding this comment.
I would call the directory here "dataclasses", where we can accumulate a series of dataclass-related examples. then we would need to have introductory documentation in the __init__.py file, see other directories in the examples/ folder for how this looks. The example script itself also needs introductory docstrings at the top. The examples get picked up by the documentation generation into sphinx docs which you can browse at https://docs.sqlalchemy.org/en/20/orm/examples.html to see what the final product looks like.
|
Hi, I don't know if this is the right place to report or it should be in the original discussion so let me know if I need to repost. I tried integrating the solution but I have The difference with the example above is that I have a model that involves Joined Table Inheritance (if I am not wrong) Compared to the example this the diff to reproduce the error --- as_is.py 2024-10-17 21:41:47
+++ with_inheritance.py 2024-10-17 21:40:07
@@ -1,4 +1,5 @@
from datetime import datetime
+from enum import Enum
from typing import Any
import sqlalchemy as sa
@@ -37,15 +38,61 @@
)
+class BalanceType(Enum):
+ user = "user"
+ company = "company"
+
+
+class Balance(Base):
+ __tablename__ = "balance"
+ __mapper_args__ = {
+ "polymorphic_identity": "__notallowed__",
+ "polymorphic_on": "type",
+ }
+
+ id: Mapped[int] = mapped_column(primary_key=True, init=False)
+ type: Mapped[BalanceType] = mapped_column(init=False)
+
+
+class UserBalance(Balance):
+ __tablename__ = "user_balance"
+ __mapper_args__ = {"polymorphic_identity": BalanceType.user}
+
+ id: Mapped[int] = mapped_column(
+ ForeignKey("balance.id"), primary_key=True, init=False
+ )
+
+ user: Mapped["User"] = relationship(back_populates="balance", default=NEVER_SET)
+
+
+class CompanyBalance(Balance):
+ __tablename__ = "company_balance"
+ __mapper_args__ = {"polymorphic_identity": BalanceType.company}
+
+ id: Mapped[int] = mapped_column(
+ ForeignKey("balance.id"), primary_key=True, init=False
+ )
+
+ company: Mapped["Company"] = relationship(
+ back_populates="balance", default=NEVER_SET
+ )
+
+
class Company(Base, TimestampsMixin):
__tablename__ = "companies"
id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True, default=None)
name: Mapped[str] = mapped_column(nullable=False, default=None)
+ balance_id: Mapped[int] = mapped_column(
+ ForeignKey("company_balance.id"), nullable=False, default=None
+ )
users: Mapped[list["User"]] = relationship(
back_populates="company", default_factory=list
)
+ balance: Mapped[CompanyBalance] = relationship(
+ back_populates="company", default=NEVER_SET
+ )
class User(Base, TimestampsMixin):
@@ -59,7 +106,13 @@
company_id: Mapped[int] = mapped_column(
ForeignKey("companies.id"), nullable=False, default=None
)
+ balance_id: Mapped[int] = mapped_column(
+ ForeignKey("user_balance.id"), nullable=False, default=None
+ )
company: Mapped[Company] = relationship(back_populates="users", default=NEVER_SET)
+ balance: Mapped[UserBalance] = relationship(
+ back_populates="user", default=NEVER_SET
+ )
applications: Mapped[list["Application"]] = relationship(
back_populates="owner", default_factory=list
@@ -84,7 +137,7 @@
session = Session(engine)
- company = Company(name="Company")
+ company = Company(name="Company", balance=CompanyBalance())
session.add(company)
session.commit()It fails at Complete error tracewith_inheritance.pyfrom datetime import datetime
from enum import Enum
from typing import Any
import sqlalchemy as sa
from sqlalchemy import ForeignKey, create_engine
from sqlalchemy.orm import (
DeclarativeBase,
Mapped,
MappedAsDataclass,
Session,
mapped_column,
relationship,
)
from sqlalchemy.orm.base import NEVER_SET
class Base(MappedAsDataclass, DeclarativeBase):
__allow_unmapped__ = True
def __post_init__(self, **kwargs: Any) -> None:
for _name, infos in sa.inspect(self.__class__).relationships.items():
if getattr(self, infos.key) == NEVER_SET:
# we have to trick the instance here otherwise it will refuse
# to delete the attribute
setattr(self, infos.key, None)
# removing the attribute in this case will avoid trashing
# the foreign_key attribute
delattr(self, infos.key)
class TimestampsMixin(MappedAsDataclass):
created_at: Mapped[datetime] = mapped_column(
default=None, server_default=sa.func.now()
)
updated_at: Mapped[datetime] = mapped_column(
default=None, server_default=sa.func.now(), onupdate=sa.func.now()
)
class BalanceType(Enum):
user = "user"
company = "company"
class Balance(Base):
__tablename__ = "balance"
__mapper_args__ = {
"polymorphic_identity": "__notallowed__",
"polymorphic_on": "type",
}
id: Mapped[int] = mapped_column(primary_key=True, init=False)
type: Mapped[BalanceType] = mapped_column(init=False)
class UserBalance(Balance):
__tablename__ = "user_balance"
__mapper_args__ = {"polymorphic_identity": BalanceType.user}
id: Mapped[int] = mapped_column(
ForeignKey("balance.id"), primary_key=True, init=False
)
user: Mapped["User"] = relationship(back_populates="balance", default=NEVER_SET)
class CompanyBalance(Balance):
__tablename__ = "company_balance"
__mapper_args__ = {"polymorphic_identity": BalanceType.company}
id: Mapped[int] = mapped_column(
ForeignKey("balance.id"), primary_key=True, init=False
)
company: Mapped["Company"] = relationship(
back_populates="balance", default=NEVER_SET
)
class Company(Base, TimestampsMixin):
__tablename__ = "companies"
id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True, default=None)
name: Mapped[str] = mapped_column(nullable=False, default=None)
balance_id: Mapped[int] = mapped_column(
ForeignKey("company_balance.id"), nullable=False, default=None
)
users: Mapped[list["User"]] = relationship(
back_populates="company", default_factory=list
)
balance: Mapped[CompanyBalance] = relationship(
back_populates="company", default=NEVER_SET
)
class User(Base, TimestampsMixin):
__tablename__ = "users"
id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True, default=None)
name: Mapped[str] = mapped_column(nullable=False, default=None)
email: Mapped[str] = mapped_column(nullable=False, default=None)
company_id: Mapped[int] = mapped_column(
ForeignKey("companies.id"), nullable=False, default=None
)
balance_id: Mapped[int] = mapped_column(
ForeignKey("user_balance.id"), nullable=False, default=None
)
company: Mapped[Company] = relationship(back_populates="users", default=NEVER_SET)
balance: Mapped[UserBalance] = relationship(
back_populates="user", default=NEVER_SET
)
applications: Mapped[list["Application"]] = relationship(
back_populates="owner", default_factory=list
)
class Application(Base, TimestampsMixin):
__tablename__ = "applications"
id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True, default=None)
name: Mapped[str] = mapped_column(nullable=False, default=None)
owner_id: Mapped[int] = mapped_column(
ForeignKey("users.id"), nullable=False, default=None
)
owner: Mapped[User] = relationship(back_populates="applications", default=None)
if __name__ == "__main__":
engine = create_engine("sqlite://")
Base.metadata.create_all(engine)
session = Session(engine)
company = Company(name="Company", balance=CompanyBalance())
session.add(company)
session.commit()
user1 = User(name="User", email="user@example.com", company=company) # works
session.add(user1)
session.commit()
user2 = User(name="User", email="user2@example.com", company_id=company.id) # works
session.add(user2)
session.commit()
application1 = Application(name="Application", owner=user1) # works
session.add(application1)
session.commit()
try:
application2 = Application(
name="Application2", owner_id=user2.id
) # does not work
session.add(application2)
session.commit()
except sa.exc.IntegrityError as e:
print(e)
|
|
you can't use NEVER_SET as a default value like that, that's why the error is being raised, that's not a valid value to assign to a mapped attribute i see a user is suggesting this as a "hacky workaround" at #9383 (comment) but this is not SQLAlchemy stuff, that's not supported looks like the discussion was looking for a new constant DONT_SET, no work has been done for that |
|
specifically it's the backref / back_populates handler that does not recognize this constant in that context |
|
Ok I think that I got my mistake. The But the problem in my case was that neither of I was a bit too quick at Find / Replace all |
|
But there is something I might have misunderstood
Isn't that "hacky workaround" exactly what is in the example proposed for this PR ? When I read your reply I got under the impression that you were endorsing it |
it looks like the example was meant to be a template for the feature itself, once implemented. Im not sure why this has to be that complicated. you can pass None and just search for that: from __future__ import annotations
from typing import Any
from sqlalchemy import create_engine
from sqlalchemy import ForeignKey
from sqlalchemy import inspect
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.orm import Mapped
from sqlalchemy.orm import mapped_column
from sqlalchemy.orm import MappedAsDataclass
from sqlalchemy.orm import relationship
from sqlalchemy.orm import Session
class Base(MappedAsDataclass, DeclarativeBase):
def __post_init__(self, **kwargs: Any) -> None:
for name in inspect(self.__class__).relationships.keys():
if self.__dict__.get(name, False) is None:
delattr(self, name)
class A(Base):
__tablename__ = "a"
id: Mapped[int] = mapped_column(primary_key=True, init=False)
data: Mapped[str]
b_id: Mapped[int] = mapped_column(ForeignKey("b.id"))
b: Mapped[B] = relationship("B", default=None)
class B(Base):
__tablename__ = "b"
id: Mapped[int] = mapped_column(primary_key=True)
data: Mapped[str]
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
a1 = A(data='x', b_id=5)
s = Session(e)
b = B(id=5,data='b1')
s.add(b)
a1 = A(data='x', b_id=5)
s.add(a1)
s.commit()
|
|
Okay thank you even better |
|
the "DONT_SET_ME" constant still keeps seeming like a good idea here but I dont like how it works against both the philosophy of dataclasses as well as SQLAlchemy's own philosophy that you shouldn't be trying to populate objects in two different ways (fk id vs. object) |
|
Thanks for the replies and sorry for the delay. So your example works fine but if you try to pass the foreign object and not the foreign key it does not: a2 = A(data='x', b=B(id=6, data='b2'))
s.add(a2)
s.commit()will fail My wish is to be able to use either the foreign key or the foreign object entirely with no error and being wired correctly, and potentially raise an error if both are passed to the init function with different id. It is currently possible to do the following though: a2 = A(data="pouet", b_id=6, b=B(id=6, data="b2"))
s.add(a2)
s.commit()but it feels wrong and error prone having to repeat b and b_id as: a3 = A(data="toto", b_id=7, b=B(id=8, data="b3"))
s.add(a3)
s.commit()after the commit, But if I put So solution is to use: class Base(MappedAsDataclass, DeclarativeBase):
def __post_init__(self, **kwargs: Any) -> None:
for name in inspect(self.__class__).relationships.keys():
if self.__dict__.get(name, False) is None:
delattr(self, name)and set But it still feels weird to add this to non-nullable fields, just to accommodate types. |
|
this example is not necessary going forward as the overall issue will be fixed in 2.1 with #12168 |
5 participants
Description
This is a working example describing the issue regarding models mapped as dataclass with relationship.
Currently it’s not possible to provide the relationship with only the foreign_key as it will be overriden by the relationship object.
I already put a comment on an existing discussion here #9383 (comment)
Checklist
This pull request is:
must include a complete example of the issue. one line code fixes without an
issue and demonstration will not be accepted.
Fixes: #<issue number>in the commit messageinclude a complete example of how the feature would look.
Fixes: #<issue number>in the commit messageHave a nice day!