SQLAlchemy Order joined table by field in another joined table - python-3.x

Question

My project requires that Orders are split into their individual lines which can be displayed in their own views I want these views to order the lines by eta which is a value in the Order table.
I have 3 tables with a 1>1 join on tables 1&2 and a many>many join on tables 2 and 3 defined by table 4 as follows:
class Order(db.Model):
id = db.Column(db.Integer, primary_key=True)
eta = db.Column(db.DateTime())
order_lines = db.relationship('Line', backref='order', order_by=lambda: Line.id)
def __repr__(self):
return '<Order No. {}>'.format(self.increment_id)
class Line(db.Model):
id = db.Column(db.Integer, primary_key=True)
line_name = db.Column(db.String())
order_id = db.Column(db.Integer, db.ForeignKey('order.id'))
product_id = db.Column(db.String, db.ForeignKey('product.product_id'))
def __repr__(self):
return '<Line SKU: {}>'.format(self.line_sku)
class Line_view(db.Model):
id = db.Column(db.Integer, primary_key=True)
view_name = db.Column(db.String())
view_lines = relationship('Line',
secondary='line_view_join',
backref='views',
lazy='dynamic',
order_by= ***???*** ) #ordery by eta on Order table
def __repr__(self):
return '<View: {}>'.format(self.view_name)
class Line_view_join(db.Model):
__tablename__ = 'line_view_join'
id = db.Column(db.Integer(), primary_key=True)
line_id = db.Column(db.Integer(), db.ForeignKey('line.id', ondelete='CASCADE'))
view_id = db.Column(db.Integer(), db.ForeignKey('line_view.id', ondelete='CASCADE'))
I am trying to work out how to query table 3, Line_View and have the joined Lines ordered by the eta of Order table.
Such that when querying:
chosen_view = Line_view.query.filter_by(id = 1).one()
chosen_view.view_lines are ordered by Order.eta
I have Tried
class Line_view(db.Model):
id = db.Column(db.Integer, primary_key=True)
view_name = db.Column(db.String())
view_lines = relationship('Line',
secondary='line_view_join',
backref='views',
lazy='dynamic',
**order_by=lambda: asc(Line.order.eta))**
def __repr__(self):
return '<View: {}>'.format(self.view_name)
But this results in the error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator' object associated with Line.order has an attribute 'eta'

Answer 1

Do you need to store the Line_views in the database? If not, you can query the Lines sorted by the eta attribute of the related order. Below, I create two orders with one line each, and then query the lines sorted by the eta attribute of their order:
eta = datetime(2019,10,10)
o = Order(eta = eta)
l = Line(order=o, line_name="sample")
db.session.add(o)
db.session.add(l)
eta = datetime(2019,11,11)
o1 = Order(eta = eta)
l1 = Line(order=o1, line_name="sample1")
db.session.add(o1)
db.session.add(l1)
db.session.commit()
lines = Line.query.join(Order).order_by(Order.eta)