使用外键和Python / sqlAlchemy的另一列设置复合键

Question

I have two tables set up in Python with sqlalchemy using mySQL. They look something like this:

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

class Test(Base):
    __tablename__ = 'test'
    id = Column(Integer, primary_key=True)
    questions = relationship('Question', cascade='all,delete', backref='test', uselist=True)

class Question(Base):
    __tablename__ = 'question'
    testID = Column(Integer, ForeignKey('test.id', ondelete='CASCADE'))
    sequence = Column(Integer, primary_key=True)
    text = Column(String(500))

Right now when I run my code and get the tables set up, they look like this:

testID|sequence|text

1 | 1 | text

1 | 2 | text

1 | 3 | text

1 | 4 | text

2 | 5 | text

2 | 6 | text

2 | 7 | text

But I want them to look like this:

testID|sequence|text

1 | 1 | text

1 | 2 | text

1 | 3 | text

1 | 4 | text

2 | 1 | text

2 | 2 | text

2 | 3 | text

I know that sequence is auto-incrementing because it is the first int primary key, but I only want it to auto-increment until there's a new testID.

I could leave it and just sort them later, but I'd really like to set it up where sequence resets with every new testID. I'm pretty new to sqlAlchemy so I may be missing something obvious. Any help is appreciated. Thanks.

Answer 1

I was able to figure this out after getting the following response from another forum .

MySQL's autoincrement feature is strictly a single integer that increases steadily. If you want an integer that is cycling, you'd need to maintain that number yourself on the Python side. Additionally, you'd want to set up a composite primary key on Question. The orderinglist extension is a quick way to get the counting-per-collection effect you are looking for (works on the Python side though and it can get tripped up if you push it too far):

from sqlalchemy import * 
from sqlalchemy.orm import * 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy.ext.orderinglist import ordering_list 
Base = declarative_base() 


class Test(Base): 
    __tablename__ = 'test' 
    id = Column(Integer, primary_key=True) 
    questions = relationship( 
        'Question', cascade='all,delete', backref='test', uselist=True, 
        collection_class=ordering_list("sequence", count_from=1)) 


class Question(Base): 
    __tablename__ = 'question' 
    testID = Column(Integer, ForeignKey('test.id', ondelete='CASCADE'), 
                    primary_key=True) 
    sequence = Column(Integer, primary_key=True) 
    text = Column(String(500)) 

e = create_engine("sqlite://", echo=True) 
Base.metadata.create_all(e) 
s = Session(e) 


s.add_all([ 
    Test( 
        questions=[ 
            Question(text="t1q1"), 
            Question(text="t1q2"), 
            Question(text="t1q3"), 
            Question(text="t1q4"), 
        ] 
    ), 
    Test( 
        questions=[ 
            Question(text="t2q1"), 
            Question(text="t2q2"), 
            Question(text="t2q3"), 
            Question(text="t2q4"), 
        ] 
    ) 
]) 

s.commit()