On 02/08/2017 03:06 PM, Andrew M wrote:
Hi,
I'm stuck on a query which might be a PostGIS problem, sorry, but in
case it relates to the SQLAlchemy side (or someone can help regardless)
I'm posting it here.
I want to run a query which returns every point which falls within a
rectangle, where the points and the rectangle are based on real-world
longitudes and latitudes.
This is the query which fails:
results = session.query(Store.id).filter(func.ST_Within(Store.location,
func.ST_GeomFromEWKT('SRID=4326;POLYGON((150 -33, 152 -33, 152 -31, 150
-31, 150 -33))')))
It runs without complaint, but when calling results.first(), I see the
following errors and warnings:
sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) function
st_within(geography, geometry) does not exist
LINE 3: WHERE ST_Within(store.location, ST_GeomFromEWKT('SRID=4326;P...
^
HINT: No function matches the given name and argument types. You might
need to add explicit type casts.
[SQL: 'SELECT store.id AS store_id \nFROM store \nWHERE
ST_Within(store.location, ST_GeomFromEWKT(%(ST_GeomFromEWKT_1)s
)) \n LIMIT %(param_1)s'] [parameters: {'ST_GeomFromEWKT_1':
'SRID=4326;POLYGON((150 -33, 152 -33, 152 -31, 150 -31, 150
-33))', 'param_1': 1}]
I can make the query work, however, by creating a dummy point in the
query (which causes every store to be matched):
results =
session.query(Store.id).filter(func.ST_Within(func.ST_GeomFromEWKT('SRID=4326;POINT(151
-32)'), func.ST_GeomFromEWKT('SRID=4326;POLYGON((150 -33, 152 -33, 152
-31, 150 -31, 150 -33))')))
This would indicate that the problem is my Store.location field, but
nothing I've tried [including type_coerce(Store.location, Geoography)]
has worked.
did you try cast() ? this is a SQL side issue so the appropriate CAST
would be needed to ensure Postgresql sees the expected types inside of
st_within().
however, cast(Store.location, Geography) seems like it would still not
work, because PG is telling you those are not the types expected by
st_within:
function st_within(geography, geometry) does not exist
per first hit on google:
http://postgis.net/docs/ST_Within.html
the correct types are:
boolean ST_Within(geometry A, geometry B);
so you'd need to CAST to geometry, not geography.
This is my SQLAlchemy definition for the location column:
location = Column(Geography(geometry_type='POINT', srid=4326))
This is the code I ran to turn longitude & latitude into a location (and
I've also tried using func.ST_GeomFromEWKT() to coerce the type):
stores = session.query(Store)
for store in stores:
store.location = 'SRID=4326;POINT({} {})'.format(store.longitude,
store.latitude)
session.commit()
Python tells me that the type of Store.location is
'geoalchemy2.elements.WKBElement', which is what I'd expect from the
documentation.
Does anyone have any suggestions on how to fix the query, please?
FYI I'm running:
- Python 3.6
- PostgreSQL 9.6.1
- PostGIS 2.3.2
- psycopg2 2.6.2
- SQLAlchemy 1.1.4, and
- Geoalchemy2 0.4.0
Thanks,
Andrew
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http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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