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我幾乎想出如何此查詢到SQLAlchemy翻譯：的SQLAlchemy從子查詢中有兩個選擇加入
select u.* from (select
unit_id,
activity,
max(occurred_at) maxOA
from Activity
group by unit_id) a1
inner join Activity a2 on
a2.unit_id = a1.unit_id and a2.occurred_at = a1.maxOA
inner join Unit u on
u.id = a2.unit_id where a2.activity = 'activateReq';
我的表是這樣的（GDB是保存我的SQLAlchemy的數據庫連接的全局變量）：
class Unit(gDB.Model):
__tablename__ = 'Unit'
id = gDB.Column('id', gDB.Integer(), primary_key=True)
owner_id = gDB.Column('owner_id', gDB.ForeignKey('User.id'))
owner = gDB.relationship(User, primaryjoin=owner_id == User.id)
unitNumber = gDB.Column('unit_number', gDB.Integer())
street = gDB.Column('street', gDB.String(255))
city = gDB.Column('city', gDB.String(255))
state = gDB.Column('state', gDB.String(2))
zip = gDB.Column('zip', gDB.String(9))
serviceInstallDate = gDB.Column('service_install_date', gDB.DateTime())
activity = gDB.relationship('Activity', backref='unit_id', lazy='select', order_by="desc(Activity.occurredAt)")
def __repr__(self):
return '<Unit: {0} {1}>'.format(self.unitNumber, self.street)
class Activity(gDB.Model):
__tablename__ = 'Activity'
id = gDB.Column('id', gDB.Integer(), primary_key=True)
unitID = gDB.Column('unit_id', gDB.ForeignKey('Unit.id'))
unit = gDB.relationship(Unit, primaryjoin=unitID == Unit.id)
agentID = gDB.Column('agent_id', gDB.ForeignKey('User.id'))
agent = gDB.relationship(User, primaryjoin=agentID == User.id)
occurredAt = gDB.Column('occurred_at', gDB.DateTime())
activity = gDB.Column('activity', gDB.String(32))
notes = gDB.Column('notes', gDB.String())
def __repr__(self):
return '<Activity: {0} {1}>'.format(self.activity, self.occurredAt)
我這個地步得到：
db.session.query(Activity.unitID, Activity.activity, func.max(Activity.occurredAt).label("maxOA"))
.group_by(Activity.unitID)
.subquery()
a2 = expression.alias(Activity)
u = expression.alias(Unit)
q = db.session.query(a1)
.join(a2, and_(a2.c.unit_id == a1.c.unit_id, a2.c.occurred_at == a1.c.maxOA))
.join(u, u.c.id == a2.c.unit_id).filter(a2.c.activity == 'activateReq')
q.all()
q.all()正在返回正確的一組行，但我希望列的Unit，而不是子查詢a1。
更新
我已經得到接近：關鍵是要query()所需的列（在這種情況下，u所有列），然後select_from()子查詢a1：
q = db.session.query(u).select_from(a1).join(a2, and_(a2.c.unit_id == a1.c.unit_id, a2.c.occurred_at == a1.c.maxOA)).join(u, u.c.id == a2.c.unit_id).filter(a2.c.activity=='activateReq')
現在的問題是生成的Unit實例沒有相關的User（owner_id/owner）對象;我的神社模板試圖引用user.owner和我
'sqlalchemy.util._collections.result object' has no attribute 'owner'
我也有不知道這是否是做到這一點的最簡潔或性能方法。