Flask SQLAlchemy 外键关系 [英] Flask SQLAlchemy Foreign Key Relationships

问题描述

我在处理 SQLAlchemy 中的外键和关系时遇到了很多麻烦.我的数据库中有两个表.第一个是Request，第二个是Agent.每个Request包含一个Agent，每个Agent有一个Request.

I'm having a lot of trouble getting my head around foreign keys and relationships in SQLAlchemy. I have two tables in my database. The first one is Request and the second one is Agent. Each Request contains one Agent and each Agent has one Request.

class Request(db.Model):
    __tablename__ = 'request'
    reference = db.Column(db.String(10), primary_key=True)
    applicationdate = db.Column(db.DateTime)
    agent = db.ForeignKey('request.agent'),

class Agent(db.Model):
    __tablename__ = 'agent'
    id =     db.relationship('Agent', backref='request', \
    lazy='select')
    name = db.Column(db.String(80))
    company = db.Column(db.String(80))
    address = db.Column(db.String(180))

当我运行 db.create_all() 时出现以下错误

When I am running db.create_all() I get the following error

无法为表 'applicant' 上的 ForeignKey 'request.agent' 初始化目标列:表 'request' 没有名为 'agent' 的列

Could not initialize target column for ForeignKey 'request.agent' on table 'applicant': table 'request' has no column named 'agent'

推荐答案

查看 关于 OneToOne 关系的 SqlAlchemy 文档.首先，您需要为每个模型提供一个主键.然后你需要定义一个外键，它引用另一个模型的主键.现在，您可以使用允许直接访问相关模型的 backref 定义关系.

Have a look at the SqlAlchemy documentation on OneToOne relationships. First you need to supply a primary key for each Model. Then you need to define one foreign key which refers to the Primary Key of the other model. Now you can define a relationship with a backref that allows direct access to the related model.

class Request(db.Model):
    __tablename__ = 'request'
    id = db.Column(db.Integer, primary_key=True)
    applicationdate = db.Column(db.DateTime)

class Agent(db.Model):
    __tablename__ = 'agent'
    id = db.Column(db.Integer, primary_key=True)   
    request_id = Column(Integer, ForeignKey('request.id'))
    request = relationship("Request", backref=backref("request", uselist=False))

    name = db.Column(db.String(80))
    company = db.Column(db.String(80))
    address = db.Column(db.String(180))

现在您可以像这样访问您的模型:

Now you can access your models like this:

request = Request.query.first()
print(request.agent.name)

agent = Agent.query.first()
print(agent.request.applicationdate)

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