通过外键模型字段验证多对多模型的唯一性

CREATE TABLE student_course (
    student_id INT NOT NULL,
    course_id INT NOT NULL,
    PRIMARY KEY (student_id, course_id),
    FOREIGN KEY (student_id) REFERENCES students(id),
    FOREIGN KEY (course_id) REFERENCES courses(id)
);

from sqlalchemy import create_engine, Table, Column, Integer, MetaData, ForeignKey
from sqlalchemy.orm import sessionmaker

engine = create_engine('sqlite:///example.db')
metadata = MetaData()

students = Table('students', metadata,
    Column('id', Integer, primary_key=True),
)

courses = Table('courses', metadata,
    Column('id', Integer, primary_key=True),
)

student_course = Table('student_course', metadata,
    Column('student_id', Integer, ForeignKey('students.id'), primary_key=True),
    Column('course_id', Integer, ForeignKey('courses.id'), primary_key=True)
)

metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()

try:
    session.execute(student_course.insert().values(student_id=1, course_id=1))
    session.execute(student_course.insert().values(student_id=1, course_id=1))  # 这将引发唯一性约束冲突
    session.commit()
except Exception as e:
    session.rollback()
    print(f"Error: {e}")