python - 从字典/JSON 构建层次结构

Question

我正在寻找一种在同一类的两个或多个实例之间以子父关系的形式创建层次结构的方法。

如何像示例中那样从嵌套字典创建此类对象？这可能吗？有没有其他推荐的方法来完成这样的任务？

# -*- coding: utf-8 -*-

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine, exists
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer, String

Base = declarative_base()

class Person(Base):
    __tablename__ = 'person';
    id = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)
    parent_id = Column(Integer, ForeignKey('person.id'))

    def __init__(self, **kwargs):
        self.parent_id = kwargs.get('parent_id', None)
        self.name = kwargs.get('name')
        self.team = kwargs.get('team', [])
        # Is it possible to create more object of this type
        # and establish that their parent_id is ID of this object?


    def __repr__(self):
        return """
        ID: {}
        Name: {}
        ParentID: {}
                """.format(self.id, self.name, self.parent_id)


engine = create_engine('sqlite:///db.sqlite3')
Base.metadata.create_all(engine)
connection = engine.connect()
Session = sessionmaker(bind=engine)
session = Session()

alice = {'name' : 'Alice'}
bob = {'name' : 'Bob', 'team' : [alice, ]}

p1 = Person(bob)
session.add(p1)
session.commit()

我了解迭代方法，我首先创建父对象，然后遍历可能的子对象并创建它们。我很好奇是否有一种方法可以在构造函数内部而不是从“外部”使用循环来执行此操作。

Answer 1

试试这个。

#your import statements including "relationship"

Base = declarative_base()


class Person(Base):
    __tablename__ = 'person'
    id = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)
    parent_id = Column(Integer, ForeignKey('person.id'))

    team = relationship("Person")  

    def __init__(self, **kwargs):
        self.parent_id = kwargs.get('parent_id', None)
        self.name = kwargs.get('name')
        team_kwargs = kwargs.get('team', [])
        for member_kwargs in team_kwargs:
            new_person = Person(**member_kwargs)
            new_person.parent_id = self.id
            self.team.append(new_person)
        # Is it possible to create more object of this type
        # and establish that their parent_id is ID of this object?
    
    def __repr__(self):
        return """
        ID: {}
        Name: {}
        ParentID: {}
                """.format(self.id, self.name, self.parent_id)


engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
connection = engine.connect()
Session = sessionmaker(bind=engine)
session = Session()



alice = {'name' : 'Alice'}
joe = {'name' : 'Joe'}
anne = {'name' : 'Anne', 'team': [alice]}
bob = {'name' : 'Bob', 'team' : [anne, joe]}

p1 = Person(**bob) 

session.add(p1)   
session.commit()

for person in session.query(Person).all():
    print(person)

输出:

    ID: 1
    Name: Bob
    ParentID: None
            

    ID: 2
    Name: Anne
    ParentID: 1
            

    ID: 3
    Name: Joe
    ParentID: 1
            

    ID: 4
    Name: Alice
    ParentID: 2

当我在一个已保存的数据库上运行它时，(engine = create_engine('sqlite:///delme.db')，并多次运行它，它在单个数据库上创建了所有条目添加并提交。

不同的方法

您还可以创建一个单独的“teams”表来存储组长和组员

# your imports and "from sqlalchemy import create_engine, Table"

Base = declarative_base()

teams = Table("teams", Base.metadata,
              Column("leader", Integer, ForeignKey("person.id"), primary_key=True),
              Column("member", Integer, ForeignKey("person.id"), primary_key=True),
              )


class Person(Base):
    __tablename__ = 'person'
    id = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)

    team = relationship("Person",
                        secondary=teams,
                        primaryjoin=id==teams.c.leader,
                        secondaryjoin=id==teams.c.member,
                        )

    def __init__(self, **kwargs):
        self.name = kwargs.get('name')
        team_input = kwargs.get('team', [])
        for member in team_input:
            new_person = Person(**member)
            self.team.append(new_person)

        def __repr__(self):
    return "ID: {}  Name: {}".format(self.id, self.name)

engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
connection = engine.connect()
Session = sessionmaker(bind=engine)
session = Session()

alice = {'name' : 'Alice'}
joe = {'name' : 'Joe'}
anne = {'name' : 'Anne', 'team': [alice]}
bob = {'name' : 'Bob', 'team' : [anne, joe]}

p1 = Person(**bob)
session.add(p1)
session.commit()

for person in session.query(Person).all():
    print(person)


for team in session.query(teams).all():
    print(team)

输出:

ID: 1  Name: Bob
ID: 2  Name: Anne
ID: 3  Name: Alice
ID: 4  Name: Joe
(1, 2)  # anne and joe are on bob's team
(1, 4)
(2, 3)  # alice is on anne's team