Your HAVING
is handled correctly, but you're passing it the wrong expression. It seems that you're using Python 2, since the relational comparison between a string and an integer
'distance' < 25
does not raise an exception, but evaluates to False
instead. In other words your query is equal to
locations = db.session.query(...).having(False).all()
which explains why you get zero results: all rows are explicitly filtered out by the HAVING clause, as seen in the printed version:
...
HAVING false = 1 -- remove all rows
A solution is to use a suitable construct, such as column()
, to produce the expression:
locations = db.session.query(...).having(column('distance') < 25).all()
You shouldn't wrap the complex select list item expression in a select()
, which represents a SELECT statement. Either label the text()
as is:
text('( 6371 * acos( cos( radians("53.6209798282177") ) * '
'cos( radians( lat ) ) * cos( radians( lng ) - radians("13.96948162900808") ) + '
'sin( radians("53.6209798282177") ) * sin( radians( lat ) ) ) ) '
'AS distance')
or build the expression using the model:
(6371 *
func.acos(func.cos(func.radians(53.6209798282177)) *
func.cos(func.radians(Location.lat)) *
func.cos(func.radians(Location.lng) - func.radians(13.96948162900808)) +
func.sin(func.radians(53.6209798282177)) *
func.sin(func.radians(Location.lat)))).label('distance')
You could improve the readability of your query construction by making a function for the great-circle distance, and with a little bit of work you could implement a hybrid method on Location
:
import math
def gc_distance(lat1, lng1, lat2, lng2, math=math):
ang = math.acos(math.cos(math.radians(lat1)) *
math.cos(math.radians(lat2)) *
math.cos(math.radians(lng2) -
math.radians(lng1)) +
math.sin(math.radians(lat1)) *
math.sin(math.radians(lat2)))
return 6371 * ang
class Location(db.Model):
...
@hybrid_method
def distance(self, lat, lng):
return gc_distance(lat, lng, self.lat, self.lng)
@distance.expression
def distance(cls, lat, lng):
return gc_distance(lat, lng, cls.lat, cls.lng, math=func)
locations = db.session.query(
Location,
Location.distance(53.6209798282177,
13.96948162900808).label('distance')).
having(column('distance') < 25).
order_by('distance').
all()
Note that the way you use HAVING to eliminate non-group rows is not portable. For example in Postgresql the presence of HAVING clause turns a query in to a grouped query, even without a GROUP BY clause. You could use a subquery instead:
stmt = db.session.query(
Location,
Location.distance(53.6209798282177,
13.96948162900808).label('distance')).
subquery()
location_alias = db.aliased(Location, stmt)
locations = db.session.query(location_alias).
filter(stmt.c.distance < 25).
order_by(stmt.c.distance).
all()