flask-sqlalchemy에서 삽입, 제거하기 전에 작업 수행

Question

flask-sqlalchemy를 사용하여 중첩 세트 모델을 구현하려고합니다. http://docs.sqlalchemy.org/en/rel_0_9/_modules/examples/nested_sets/nested_sets.html

마법이 before_insert 자신의 정의에 일어날 것 :

나는 SQLAlchemy의 사용 예를 볼

@event.listens_for(Employee, "before_insert") 
def before_insert(mapper, connection, instance): 
    if not instance.parent: 
     instance.left = 1 
... 

나는 나에게를 대체 할 수있는 방법이 있는지 찾는 데 문제가 있었어요 비슷한 방법으로 flask-sqlalchemy 프레임 워크에서 db.session.add를 제거하십시오. 아니면 여기서 다른 일을해야합니까?

Answer 1

중첩 세트 대신 nested intervals을 구현했습니다. 여러분에게 도움이되기를 바랍니다.

class Employee(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    employee_name = db.Column(db.String(120)) 
    parent = db.Column(db.Integer, db.ForeignKey('employee.id'), index=True) 
    # implements nested intervals with fractions 
    created = db.Column(db.DateTime, index=True) 
    left_num = db.Column(db.Integer, nullable=False) 
    left_den = db.Column(db.Integer, nullable=False) 
    right_num = db.Column(db.Integer, nullable=False) 
    right_den = db.Column(db.Integer, nullable=False) 
    level = db.Column(db.Integer, nullable=False) 

    def __init__(self, employee_name, parent): 
     self.created = datetime.datetime.now() 
     self.employee_name = employee_name 
     self.parent = parent 

     # handle case of first addition 
     if not parent: 
      self.level = 1 
      left_node_num = 0 
      left_node_den = 1 
      right_node_num = 1 
      right_node_den = 1 
     else: 
      parent_employee = Employee.query.get(self.parent) 
      # if the parent exists, set level to 1 more 
      self.level = parent_employee.level + 1 
      # find the most recent sibling 
      most_recent_sibling = Employee.query\ 
       .filter_by(parent=self.parent)\ 
       .order_by(Employee.id.desc())\ 
       .first() 
      if not most_recent_sibling: 
       # if no sibling, use parent boundaries 
       left_node_num = parent_employee.left_num 
       left_node_den = parent_employee.left_den 
      else: 
       left_node_num = most_recent_sibling.right_num 
       left_node_den = most_recent_sibling.right_den 
      right_node_num = parent_employee.right_num 
      right_node_den = parent_employee.right_den 
     left_boundary = fractions.Fraction(numerator=left_node_num + right_node_num, 
              denominator=left_node_den + right_node_den) 
     right_boundary = fractions.Fraction(numerator=left_boundary.numerator + right_node_num, 
              denominator=left_boundary.denominator + right_node_den) 
     self.left_num = left_boundary.numerator 
     self.left_den = left_boundary.denominator 
     self.right_num = right_boundary.numerator 
     self.right_den = right_boundary.denominator