Question

我有两种类型的对象：

潜水员ValueObjects继承自BaseValueObject和
Addendum - 带注释的对象。

Addendum具有特定注释（属性：name，description，flag）和一般注释（(badgetype, badgevalue)），其中badgevalue是存储在Badge - 对象和badgetype in an AddendumBadgeMap`对象中。

现在，我想访问

name，description和flag作为ValueOjects和
Badges直接来自ValueOjects作为字典。

以下是一个示例实现：

import sqlalchemy as sa
import sqlalchemy.orm as orm
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base

DBSession = scoped_session(sessionmaker())
Base = declarative_base ()

###### ValueObjects: ##########
class BaseValueObject(Base):
  __tablename__ = 'value_objects'
  id = sa.Column(sa.Integer, primary_key=True)
  vo_type = sa.Column (sa.String, nullable=False)
  __mapper_args__ = {'polymorphic_on': vo_type}

class ObjectOne(BaseValueObject):
  __tablename__ = 'objects_one'
  __mapper_args__ = {'polymorphic_identity': 'ObjectOne'}
  id = sa.Column(sa.ForeignKey('value_objects.id'), primary_key=True)
  any_attribute = sa.Column(sa.String)


class ObjectTwo(BaseValueObject):
  __tablename__ = 'objects_two'
  __mapper_args__ = {'polymorphic_identity': 'ObjectTwo'}
  id = sa.Column(sa.ForeignKey('value_objects.id'), primary_key=True)
  any_attribute = sa.Column(sa.String)
###############################


##### Addendum and Bagde ##########
class Addendum(Base):
  __tablename__ = 'addenda'
  __table_args__ = (
      sa.UniqueConstraint('name', 'id'),
      {}
      )
  id = sa.Column (sa.Integer, primary_key=True)
  name = sa.Column (sa.String, nullable=False, default='')
  description = sa.Column (sa.String, nullable=False, default='')
  flag = sa.Column ( sa.Boolean, nullable=False, default=False)
  value_object_id = sa.Column ( sa.ForeignKey ('value_objects.id'),
      unique=True)


class Badge(Base):
  __tablename__ = 'badges'
  id = sa.Column (sa.Integer, primary_key=True)
  value = sa.Column (sa.String)


class AddendumBadgeMap(Base):
  __tablename__ = 'addendum_badge_maps'
  __table_args__ = (
      sa.PrimaryKeyConstraint('id'),
      sa.UniqueConstraint('badge_id', 'badge_type'),
      {}
      )
  id = sa.Column('id', sa.Integer)
  addendum_id = sa.Column(sa.ForeignKey('addenda.id'), nullable=False)
  badge_id =  sa.Column(sa.ForeignKey('badges.id'), nullable=False)
  badge_type = sa.Column (sa.String)
###################################

if __name__ == '__main__':
  engine = sa.create_engine('sqlite:///:memory:', echo=True)
  DBSession.configure(bind=engine)
  Base.metadata.create_all(engine)
  session = DBSession()

  o1 = ObjectOne(any_attribute="test1")
  session.add(o1)
  session.commit()

我必须补充一点，我可以执行以下操作：

o1.name = "my_name"
# => `Addendum` will be attached with `name="my_name"`
o1.description = "my_description"
# => `descrpiption` of the attached `Addendum` get's changed
o1.flag
# => same behavior (in general: there should be max. one `Addendum` per `ValueObject`)
o1.bagdes = {"file_origin": "/home/.."}
# => attach to the `Addendum` a `Badge` with `value="/home/.."` and
#    `AddendumBagdeMap.badge_type="file_origin"` (if `Addendum` does
#     not exist for this `ValueObject`: create it first)

Answer 1

一个解决方案需要实现两部分：

在Addendum

composite-association-proxies

从（{1}}

Addendum.badges

第1部分：复合关联代理的实施

将以下属性添加到BaseValueObject：

Addendum

以及以下badges = association_proxy ( 'addendum_badge_maps', 'badge_value', creator=lambda bt, bv: AddendumBadgeMap(badge_type=bt, badge_value=bv) )：

AddendumBadgeMap

现在，向addendum = orm.relationship(Addendum, backref=orm.backref( 'addendum_badge_maps', collection_class = attribute_mapped_collection("badge_type"), cascade="all, delete-orphan") ) badge = orm.relationship('Badge', single_parent=True, ) badge_value = association_proxy ('badge', 'value')添加__init__ - 方法：

Badge

并在顶部添加以下导入：

def __init__(self, value):
  self.value = value

第2部分：从from sqlalchemy.ext.associationproxy import association_proxy from sqlalchemy.orm.collections import attribute_mapped_collection访问badge - 代理

通过向BaseValueObjects添加属性，将Addendum - 对象链接到BaseValueObjects：

Addendum

要访问base_value_object = orm.relationship( "BaseValueObject", backref=orm.backref('addendum', uselist=False) )，请将以下内容添加到badegs：

BaseValueObjects

完整代码

def add_badge(self, badge_dict={}, **kwargs):
  if self.addendum is None:
    self.addendum = Addendum()
  badge_dict.update(kwargs)
  self.addendum.badges = badge_dict

_name = association_proxy('addendum', 'name',
    creator=lambda name: Addendum(
      name=name, description='', flag=False))
_description = association_proxy('addendum', 'description',
    creator=lambda description: Addendum(
      name='', description=description, flag=False))
_flag = association_proxy('addendum', 'flag',
    creator=lambda flag: Addendum(
      name='', description='', flag=flag))

@property
def badges(self):
  try:
    return self.addendum.badges
  except AttributeError:
    "In case that there is no ``Addendum`` specified, yet."
    return None

@badges.setter
def badges(self, value):
  self.add_badge(value)

@property
def name(self):
  try:
    return self._name
  except AttributeError:
    "In case that there is no ``Addendum`` specified, yet."
    return ""

@name.setter
def name(self, value):
  self._name = value

@property
def description(self):
  try:
    return self._description
  except AttributeError:
    "In case that there is no ``Addendum`` specified, yet."
    return ""

@description.setter
def description(self, value):
  self._description = value

@property
def flag(self):
  try:
    return self._flag
  except AttributeError:
    "In case that there is no ``Addendum`` specified, yet."
    return ""

@flag.setter
def flag(self, value):
  self._flag = value

如何使用SQLAlchemies association_proxy跨多个对象传递特定属性？

1 个答案: