Database design sqlalchemy图形数据库数据操作

我正在设计一个图形数据库结构。节点可以是个人、部门等。这就是我添加nodeType的原因。节点之间的关系也可以是多种类型。 从下面的代码中，r1和r2被插入数据库。当我读取数据库时，我看到null。为什么呢？ 我希望看到与.id字段相关的值（例如n1.id、rt1.id、n2.id）

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对代码改进的其他评论也值得赞赏。

代码的问题是，在将节点插入数据库之前，您试图使用Node.id属性。在调用

session.flush（）

或

session.commit（）

之前，新创建的对象没有id，也不能，因为生成id的是DB引擎

因此SQLAlchemy实现这一点的方法是定义

关系

对象和

节点

对象之间的关系，并在

关系中分配对象。就这样,

from sqlalchemy import MetaData, Table, Column, Integer, ForeignKey, \
    create_engine, String
from sqlalchemy.orm import mapper, relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine('sqlite:///dir_graph.sqlite', echo=True)

Base = declarative_base()
Session = sessionmaker(bind=engine)
session = Session()


class NodeType(Base):
    __tablename__ = 'nodetype'
    id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    nodes = relationship('Node', backref='nodetype')

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

    def __repr__(self):
        return "Nodetype: %s" % self.name


class Node(Base):
    __tablename__ = 'node'

    id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    type_id = Column(Integer,
                     ForeignKey('nodetype.id'))


    def __init__(self, _name, _type_id):
        self.name = _name
        self.type_id = _type_id


class Relation(Base):
    __tablename__ = 'relation'

    id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    type_id = Column(Integer,
                     ForeignKey('relationtype.id'))

    from_id = Column(Integer,
                     ForeignKey('node.id'))

    to_id = Column(Integer,
                   ForeignKey('node.id'))

    from_node = relationship(Node, primaryjoin=Node.id == from_id)
    to_node = relationship(Node, primaryjoin=Node.id == to_id)

    def __init__(self, _fromNode, _type_id, _toNode):
        self.from_node = _fromNode
        self.type_id = _type_id
        self.to_node = _toNode


class RelationType(Base):
    __tablename__ = 'relationtype'

    id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    description = Column(String(30), unique=True)

    relations = relationship('Relation', backref='relationtype')

    def __init__(self, _name):
        self.name = _name

    def description(self, _description):
        self.description = _description


Base.metadata.create_all(engine)

nt1 = NodeType('nt1')
nt2 = NodeType('nt2')

n1 = Node('n1type1', 1)
n2 = Node('n2type1', 1)
n3 = Node('n3type1', 1)
n4 = Node('n4type2', 2)
n5 = Node('n5type2', 2)

rt1 = RelationType('rt1')
rt2 = RelationType('rt2')
rt3 = RelationType('rt3')

r1 = Relation(n1, rt1.id, n2)
r2 = Relation(n3, rt2.id, n5)

session.add_all([nt1, nt2, n1, n2, n3, n4, n5, rt1, rt2, rt3, r1, r2])
session.commit()

您必须指定“读取数据库”的含义。您试图运行的查询是什么，它返回意外的空值？运行代码后，我使用SQLiteStudio读取数据库。在表关系中，我看到：id:1 name:null type:id:null from_id:null to_id:null对于id:2tanks相同，现在可以正常工作了。当我在代码运行后与解释器交互时，我得到一个线程错误。e、 g.r3=关系（n4，rt2.id，n5）是什么导致线程错误？（对不起，我是新手）谢谢
from sqlalchemy import MetaData, Table, Column, Integer, ForeignKey, \
    create_engine, String
from sqlalchemy.orm import mapper, relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine('sqlite:///dir_graph.sqlite', echo=True)

Base = declarative_base()
Session = sessionmaker(bind=engine)
session = Session()


class NodeType(Base):
    __tablename__ = 'nodetype'
    id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    nodes = relationship('Node', backref='nodetype')

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

    def __repr__(self):
        return "Nodetype: %s" % self.name


class Node(Base):
    __tablename__ = 'node'

    id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    type_id = Column(Integer,
                     ForeignKey('nodetype.id'))


    def __init__(self, _name, _type_id):
        self.name = _name
        self.type_id = _type_id


class Relation(Base):
    __tablename__ = 'relation'

    id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    type_id = Column(Integer,
                     ForeignKey('relationtype.id'))

    from_id = Column(Integer,
                     ForeignKey('node.id'))

    to_id = Column(Integer,
                   ForeignKey('node.id'))

    from_node = relationship(Node, primaryjoin=Node.id == from_id)
    to_node = relationship(Node, primaryjoin=Node.id == to_id)

    def __init__(self, _fromNode, _type_id, _toNode):
        self.from_node = _fromNode
        self.type_id = _type_id
        self.to_node = _toNode


class RelationType(Base):
    __tablename__ = 'relationtype'

    id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    description = Column(String(30), unique=True)

    relations = relationship('Relation', backref='relationtype')

    def __init__(self, _name):
        self.name = _name

    def description(self, _description):
        self.description = _description


Base.metadata.create_all(engine)

nt1 = NodeType('nt1')
nt2 = NodeType('nt2')

n1 = Node('n1type1', 1)
n2 = Node('n2type1', 1)
n3 = Node('n3type1', 1)
n4 = Node('n4type2', 2)
n5 = Node('n5type2', 2)

rt1 = RelationType('rt1')
rt2 = RelationType('rt2')
rt3 = RelationType('rt3')

r1 = Relation(n1, rt1.id, n2)
r2 = Relation(n3, rt2.id, n5)

session.add_all([nt1, nt2, n1, n2, n3, n4, n5, rt1, rt2, rt3, r1, r2])
session.commit()