如何在 SQLAlchemy 中創建一個以 Interval 作為主鍵的表？

Question

我正在嘗試使用 SQLAlchemy ORM 創建一個用於處理計費頻率的表，但我似乎不太高興

以下在 Postgres 中效果很好：

create table test_interval(
    frequency interval primary key
);


insert into test_interval values ('1 MONTH'), ('1 YEAR');


select * from test_interval;
-- 0 years 1 mons 0 days 0 hours 0 mins 0.00 secs
-- 1 years 0 mons 0 days 0 hours 0 mins 0.00 secs

我現在正在嘗試使用此代碼在 SQLAlchemy 中實現相同的目標

from typing import Any

from sqlalchemy import Column, Interval, PrimaryKeyConstraint
from sqlalchemy.ext.declarative import as_declarative, declared_attr


@as_declarative()
class Base:
    id: Any
    __name__: str

    # Generate __tablename__ automatically
    @declared_attr
    def __tablename__(cls) -> str:
        return cls.__name__.lower()



class BillingFrequency(Base):
    __tablename__ = "billing_frequency"
    # I've also tried this
    # __table_args__ = (PrimaryKeyConstraint("frequency"),)
    # frequency: Column(Interval(native=True), index=True, unique=True, nullable=False)
    frequency: Column(Interval(native=True), primary_key=True, nullable=False)


# seed.py
# -- I've not even managed to create the table so this is yet untested --
from sqlalchemy.orm import Session
from sqlalchemy.dialects.postgresql import insert

from app.models import BillingFrequency

def seed_billing(db: Session) -> None:
    # Monthy frequency
    stmt_month = insert(BillingFrequency).values(frequency="1 MONTH")
    stmt_month = stmt_month.on_conflict_do_nothing(
        index_elements=[BillingFrequency.frequency],
    )
    db.add(stmt_month)
    # Year frequency
    stmt_year = insert(BillingFrequency).values(frequency="1 YEAR")
    stmt_year = stmt_year.on_conflict_do_nothing(
        index_elements=[BillingFrequency.frequency],
    )
    db.add(stmt_year)
    db.commit()

這導致以下錯誤：

sqlalchemy.exc.ArgumentError: Mapper mapped class BillingFrequency->billing_frequency could not assemble any primary key columns for mapped table 'billing_frequency'

如果我嘗試使用__table_args__使用主鍵， __table_args__出現以下錯誤。

 KeyError: 'frequency'

不知道如何處理這個。 這在純 SQL 中非常簡單，但 ORM 讓它變得很痛苦。

Answer 1

您犯了兩個小錯誤，但不幸的是，對於此類錯誤，錯誤消息有點神秘。

第一個問題是您使用...: Column即作為類型而不是...= Column分配值。 這就是導致sqlalchemy.exc.ArgumentError和KeyError: 'frequency' ，SQLAlchemy 不知道該列存在，因為它沒有查看 Column 數據的類型注釋。

您犯的第二個錯誤是使用db.add(…)作為語句，您應該使用db.execute(…) 。 使用db.add會出現以下錯誤：

AttributeError: 'Insert' object has no attribute '_sa_instance_state'

The above exception was the direct cause of the following exception:
...
sqlalchemy.orm.exc.UnmappedInstanceError: Class 'sqlalchemy.dialects.postgresql.dml.Insert' is not mapped

通過這些更改，您的代碼應如下所示：

from typing import Any

from sqlalchemy import Column, Interval, PrimaryKeyConstraint
from sqlalchemy.ext.declarative import as_declarative, declared_attr


@as_declarative()
class Base:
    id: Any
    __name__: str

    # Generate __tablename__ automatically
    @declared_attr
    def __tablename__(cls) -> str:
        return cls.__name__.lower()



class BillingFrequency(Base):
    __tablename__ = "billing_frequency"
    frequency = Column(Interval(native=True), primary_key=True, nullable=False)


# seed.py
# -- I've not even managed to create the table so this is yet untested --
from sqlalchemy.orm import Session
from sqlalchemy.dialects.postgresql import insert

from app.models import BillingFrequency

def seed_billing(db: Session) -> None:
    # Monthy frequency
    stmt_month = insert(BillingFrequency).values(frequency="1 MONTH")
    stmt_month = stmt_month.on_conflict_do_nothing(
        index_elements=[BillingFrequency.frequency],
    )
    db.execute(stmt_month)
    # Year frequency
    stmt_year = insert(BillingFrequency).values(frequency="1 YEAR")
    stmt_year = stmt_year.on_conflict_do_nothing(
        index_elements=[BillingFrequency.frequency],
    )
    db.execute(stmt_year)
    db.commit()