SQLAlchemy加入子查询问题

Question

我正在尝试将 SQL 转换为 SQLAlchemy。我想要的查询的SQL版本如下：

SELECT * from calendarEventAttendee
JOIN calendarEventAttendanceActual ON calendarEventAttendanceActual.id = calendarEventAttendee.attendanceActualId
LEFT JOIN
   (SELECT bill.id, bill.personId, billToEvent.eventId FROM bill JOIN billToEvent ON bill.id = billToEvent.billId) b 
   ON b.eventId = calendarEventAttendee.eventId AND b.personId = calendarEventAttendee.personId
WHERE b.id is NULL

我的 SQLAlchemy 查询如下：

query = db.session.query(CalendarEventAttendee).join(CalendarEventAttendanceActual)

sub_query = db.session.query(Bill, BillToEvent).join(BillToEvent, BillToEvent.billId == Bill.id).subquery()
query = query.outerjoin(sub_query, and_(sub_query.Bill.personId == CalendarEventAttendee.personId, Bill.eventId == CalendarEventAttendee.eventId))
results = query.all()

我收到一个错误AttributeError: 'Alias' object has no attribute 'Bill'

如果我将 SQLAlchemy 查询调整为以下内容：

sub_query = db.session.query(Bill, BillToEvent).join(BillToEvent, BillToEvent.billId == Bill.id).subquery()
query = query.outerjoin(sub_query, and_(sub_query.Bill.personId == CalendarEventAttendee.personId, sub_query.BillToEvent.eventId == CalendarEventAttendee.eventId))

结果 = query.all()

我收到一个错误AttributeError: Bill

任何帮助将不胜感激，谢谢！

Answer 1

一旦调用subquery()，就无法访​​问对象，只能通过.c.{column_name} 访问器访问列。

对sub_query 执行以下操作：仅加载您需要的列以避免任何名称冲突：

sub_query = db.session.query(
        Bill.id, Bill.personId, BillToEvent.eventId
    ).join(BillToEvent, BillToEvent.billId == Bill.id).subquery()

然后在您的查询中使用带有.c.column_name 的列名：

query = query.outerjoin(
    sub_query, and_(
        sub_query.c.personId == CalendarEventAttendee.personId, 
        sub_query.c.eventId == CalendarEventAttendee.eventId)
    )
results = query.all()