查询SQLAlchemy中的相关表 [英] Querying related tables in sqlalchemy

问题描述

所以我有两个这样的表Employee和Details.

So I have two tables Employee and Details like this.

class Employee(Base):
    __tablename__ = 'employees'
    id = Column(Integer, Sequence('employee_id_seq'), primary_key=True)
    name = Column(String(50), nullable=False)
    ............

class Detail(Base):
    __tablename__ = 'details'
    id = Column(Integer, Sequence('detail_id_seq'), primary_key=True)
    start_date = Column(String(50), nullable=False)
    email = Column(String(50))
    employee_id = Column(Integer, ForeignKey('employee.id'))
    employee = relationship("Employee", backref=backref('details', order_by=id))
    ............

现在我要做的是获取所有员工及其相应的详细信息，这是我尝试过的.

Now what I want to do is get all the employees and their corresponding details, here is what I tried.

for e, d in session.query(Employee, Detail).filter(Employee.id = Detail.employee_id).all():
    print e.name, d.email

此问题是它将所有内容打印两次.我尝试使用.join()，并且还将结果打印两次.

The problem with this is that it prints everything twice. I tried using .join() and also prints the results twice.

我想实现的目标是

print Employee.name
print Employee.details.email

推荐答案

如果您只关心很少的列，则可以在查询中直接指定它们:

If you really care only about few columns, you can specify them in the query directly:

q = session.query(Employee.name, Detail.email).filter(Employee.id == Detail.employee_id).all()
for e, d in q:
    print e, d

如果您确实要加载对象实例，那么我会做不同的事情:

If you do really want to load object instances, then I would do it differently:

# query all employees
q = (session.query(Employee)
        # load Details in the same query
        .outerjoin(Employee.details)
        # let SA know that the relationship "Employee.details" is already loaded in this query so that when we access it, SA will not do another query in the database
        .options(contains_eager(Employee.details))
        ).all()

# navigate the results simply as defined in the relationship configuration
for e in q:
    print(e)
    for d in e.details:
        print(" ->", d)

关于您的duplicate结果问题，我相信您的真实代码中会产生一些额外"错误……

As to your duplicate result problem, I believe you have some "extra" in your real code which produces this error...

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