我有以下關系： acourse有很多course_instances，每個都course_instance屬于 a semester。這是一組大大簡化的模型：class Course(db.Model):    __tablename__ = "courses"    id = Column(Integer, primary_key=True)    course_instances = relationship("CourseInstance", back_populates="course")class CourseInstance(db.Model):    __tablename__ = "course_instances"    id = Column(Integer, primary_key=True)    course_id = Column(Integer, ForeignKey("courses.id"))    semester_id = Column(Integer, ForeignKey("semesters.id"))    course = relationship("Course", back_populates="course_instances")    semester = relationship("Semester", back_populates="course_instances")class Semester(db.Model):    __tablename__ = "semesters"    id = Column(Integer, primary_key=True)    sort_ix = Column(Integer)    course_instances = relationship("CourseInstance", back_populates="semester")我經常在什么時候查詢一門課程并將所有實例包含在joinedload/contains_eager/selectinload. 這些實例應始終按sort_ix每個實例所在學期的列排序。有沒有辦法在課程模型級別指定此默認順序？是這樣的：course_instances = relationship(    "CourseInstance",    back_populates="course",    order_by="CourseInstance.semester.sort_ix")我唯一能想到的就是為CourseInstancelike添加一個重復的列semester_sort_ix。