Pyramid/SQLAlchemy 显示对象

Question

我正在创建一个记录系统，学生可以在其中注册一个班级。

# MODEL
class Association(Base):
__tablename__ = 'association'
class_id = Column(Integer, ForeignKey('classes.id'), primary_key=True)
student_id = Column(Integer, ForeignKey('students.id'), primary_key=True)
theClass = relationship("Class")

class Student(Base):
__tablename__ = 'students'
id = Column(Integer, primary_key=True)
name = Column(String(30))
classlist = relationship("Association", backref='student')

class Class(Base):
__tablename__ = 'classes'
id = Column(Integer, primary_key=True)
name = Column(String(20), nullable=False)
teacher_id = Column(Integer, ForeignKey('teachers.id'))
enrolled_students = relationship("Association")

我想显示所有尚未注册课程的学生，所以我在我的程序和模板中使用了以下代码，但它只显示页面上的所有学生。

currentClass = session.query(Class).filter_by(id=class_id).first()
students = session.query(Student).all()

# TEMPLATE
% for st in students:
% for assoc in currentClass.enrolled_students:
% if st.id != assoc.student_id:
    <input type="checkbox" name="student_id" value="${ st.id }" >${ st.id } - ${ st.forename } ${ st.surname }</input><br/> 
% endif
% endfor
% endfor

Answer 1

我认为您的代码甚至输出每个学生姓名的次数与当前班级中的学生人数一样多（如果学生已注册班级，则减一）:)

你现在的逻辑是

for student in all_student:  # Alice, Bob, Claude
    for enrolled_student in current_class.enrolled_students: # Alice, Bob
        if student != enrolled_student:
            print student

上面的输出是

Alice, Alice, Bob, Bob, Claude, Claude, Claude  

（第一次迭代：Alice == Alice，跳过。第二次：Alice ！= Bob，打印。第三次：Alice ！= Claude，打印等）

您的关系设置也不是“惯用的 sqlalchemy”。看看http://docs.sqlalchemy.org/en/rel_0_9/orm/relationships.html#many-to-many 如果您按照示例设置模型（例如使用relationship() 函数的secondary 参数），您将能够执行类似的操作

% for st in students:
% if st not in class.enrolled_students:
    <input type="checkbox" name="student_id" value="${ st.id }" >${ st.id } - ${ st.forename } ${ st.surname }</input><br/> 
% endif
% endfor

Answer 2

你的查询全错了..

students = Session.query(Student).\
            filter(Student.classlist == None).all()

for student ins students:
     <input type="checkbox" name="student_id" value="${ st.id }" >${ st.id } - ${ st.forename } ${ st.surname }</input><br/>
endfor