【问题标题】：Nested one-to-many relationship sqlalchemy filtering嵌套的一对多关系 sqlalchemy 过滤
【发布时间】：2021-12-17 14:58:34
【问题描述】：

我试图在 sqlalchemy 中过滤嵌套的一对多关系，但它只在内部连接（第二个）中提供过滤器，我如何在外部连接而不是内部连接中指定过滤器？

我有

一对多学校 -->课程
一对多班级 -> 学生

我试图让特定学校、特定班级的所有学生

模型.py

class School(Base):
    __tablename__ = 'schools'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    #  # Relationship for one-many - parent of classes
    classes = relationship("Class")

    def __repr__(self):
        return "<School(name='%s')>" % self.name

class Class(Base):
    __tablename__ = 'classes'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    # foreign Key for the parent - child of school
    school_id = Column(Integer, ForeignKey('schools.id'))
    # Relationship for one-many - parent of students
    students = relationship("Student")

    def __repr__(self):
        return "<Class(name='%s')>" % self.name

class Student(Base):
    __tablename__ = 'students'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    nickname = Column(String)
    # foreign Key for the parent - child of school
    class_id = Column(Integer, ForeignKey('classes.id'))

    def __repr__(self):
        return "<Student(name='%s', fullname='%s', nickname='%s')>" % (
            self.name, self.fullname, self.nickname)

查询是

info = session.query(SchoolModel). \
                options(subqueryload(SchoolModel.classes).subqueryload(ClassModel.students)). \
                filter(SchoolModel.id == parent_lookup_class__student). \
                filter(ClassModel.id == parent_lookup_class). \
                filter(StudentModel.id == pk). \
                first()

输出为所有学生提供与其相关的所有信息，我的查询有什么问题？

【问题讨论】：

标签： django sqlalchemy

【解决方案1】：

问题是我正在使用subqueryload，它实际上无法修改，而是我使用contains_eager() 过滤我的结果新查询是

 info = session.query(SchoolModel). \
            join(SchoolModel.classes). \
            join(ClassModel.students). \
            options(contains_eager(SchoolModel.classes), contains_eager(SchoolModel.classes, ClassModel.students)). \
            filter(SchoolModel.id == parent_lookup_class__student). \
            filter(ClassModel.id == parent_lookup_class). \
            filter(StudentModel.id == pk). \
            populate_existing(). \
            first()

【讨论】：