Hello
I created my own type, Geometry, to deal with PostGIS' geometry column type.
----
class Geometry(TypeEngine):
def __init__(self, srid=-1, dims=2):
super(Geometry, self).__init__()
self.srid = srid
self.dims = dims
def get_col_spec(self):
return 'GEOMETRY()'
def compare_values(self, x, y):
return x.equals(y)
def convert_bind_param(self, value, engine):
"""convert value from a geometry object to database"""
if value is None:
return None
else:
return "SRID=%s;%s" % (self.srid, value.wkb.encode('hex'))
def convert_result_value(self, value, engine):
"""convert value from database to a geometry object"""
if value is None:
return None
else:
return loads(value.decode('hex'))
----
So far, so good; user can do:
wifi_table = Table('wifi', metadata,
Column('the_geom', Geometry(4326)),
autoload=True)
But ultimately I'd like that my users can do:
wifi_table = Table('wifi', metadata, autoload=True)
I tried this:
from sqlalchemy.databases import postgres
postgres.ischema_names['geometry'] = Geometry
This is ok, but during reflection, when SQLA creates Geometry objects,
it obviously passes no "srid" argument to the Geometry constructor, so
the Geometry objects all end up with the "srid" property set to -1.
The proper "srid" value to pass to the Geometry constructor is
actually in a PostGIS table (geometry_columns). So if a geometry
column is discovered, the table's "srid" value could be read from that
table and passed to the Geometry constructor. I thought about doing
something like that:
from sqlalchemy.databases import postgres
def geometry_factory():
// go read srid associated with table from geometry_columns
srid =
return Geometry(srid)
postgres.ischema_names['geometry'] = geometry_factory
but geometry_factory doesn't have any connection object to go read the
srid value.
My question is simple: do you see solutions to my problem?
Thanks,
--
Eric
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