Note
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Automatically use a function at insert or selectΒΆ
Sometimes the application wants to apply a function in an insert or in a select.
For example, the application might need the geometry with lat/lon coordinates while they
are projected in the DB. To avoid having to always tweak the query with a
ST_Transform()
, it is possible to define a TypeDecorator
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import pytest
import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy import MetaData
from sqlalchemy import Column
from sqlalchemy import Integer
from sqlalchemy import func
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from sqlalchemy.types import TypeDecorator
from geoalchemy2.compat import PY3
from geoalchemy2 import Geometry
from geoalchemy2 import shape
engine = create_engine('postgresql://gis:gis@localhost/gis', echo=True)
metadata = MetaData(engine)
Base = declarative_base(metadata=metadata)
class TransformedGeometry(TypeDecorator):
"""This class is used to insert a ST_Transform() in each insert or select."""
impl = Geometry
def __init__(self, db_srid, app_srid, **kwargs):
kwargs["srid"] = db_srid
self.impl = self.__class__.impl(**kwargs)
self.app_srid = app_srid
self.db_srid = db_srid
def column_expression(self, col):
"""The column_expression() method is overrided to ensure that the
SRID of the resulting WKBElement is correct"""
return getattr(func, self.impl.as_binary)(
func.ST_Transform(col, self.app_srid),
type_=self.__class__.impl(srid=self.app_srid)
# srid could also be -1 so that the SRID is deduced from the
# WKB data
)
def bind_expression(self, bindvalue):
return func.ST_Transform(
self.impl.bind_expression(bindvalue), self.db_srid)
class ThreeDGeometry(TypeDecorator):
"""This class is used to insert a ST_Force3D() in each insert."""
impl = Geometry
def bind_expression(self, bindvalue):
return func.ST_Force3D(self.impl.bind_expression(bindvalue))
class Point(Base):
__tablename__ = "point"
id = Column(Integer, primary_key=True)
raw_geom = Column(Geometry(srid=4326, geometry_type="POINT"))
geom = Column(
TransformedGeometry(
db_srid=2154, app_srid=4326, geometry_type="POINT"))
three_d_geom = Column(
ThreeDGeometry(srid=4326, geometry_type="POINTZ", dimension=3))
session = sessionmaker(bind=engine)()
def check_wkb(wkb, x, y):
pt = shape.to_shape(wkb)
assert round(pt.x, 5) == x
assert round(pt.y, 5) == y
class TestTypeDecorator():
def setup(self):
metadata.drop_all(checkfirst=True)
metadata.create_all()
def teardown(self):
session.rollback()
metadata.drop_all()
def _create_one_point(self):
# Create new point instance
p = Point()
p.raw_geom = "SRID=4326;POINT(5 45)"
p.geom = "SRID=4326;POINT(5 45)"
p.three_d_geom = "SRID=4326;POINT(5 45)" # Insert 2D geometry into 3D column
# Insert point
session.add(p)
session.flush()
session.expire(p)
return p.id
def test_transform(self):
self._create_one_point()
# Query the point and check the result
pt = session.query(Point).one()
assert pt.id == 1
assert pt.raw_geom.srid == 4326
check_wkb(pt.raw_geom, 5, 45)
assert pt.geom.srid == 4326
check_wkb(pt.geom, 5, 45)
# Check that the data is correct in DB using raw query
q = "SELECT id, ST_AsEWKT(geom) AS geom FROM point;"
res_q = session.execute(q).fetchone()
assert res_q.id == 1
assert res_q.geom == "SRID=2154;POINT(857581.899319668 6435414.7478354)"
# Compare geom, raw_geom with auto transform and explicit transform
pt_trans = session.query(
Point,
Point.raw_geom,
func.ST_Transform(Point.raw_geom, 2154).label("trans")
).one()
assert pt_trans[0].id == 1
assert pt_trans[0].geom.srid == 4326
check_wkb(pt_trans[0].geom, 5, 45)
assert pt_trans[0].raw_geom.srid == 4326
check_wkb(pt_trans[0].raw_geom, 5, 45)
assert pt_trans[1].srid == 4326
check_wkb(pt_trans[1], 5, 45)
assert pt_trans[2].srid == 2154
check_wkb(pt_trans[2], 857581.89932, 6435414.74784)
@pytest.mark.skipif(
not PY3 and parse_version(str(sqlalchemy.__version__)) < parse_version("1.3"),
reason="Need sqlalchemy >= 1.3")
def test_force_3d(self):
self._create_one_point()
# Query the point and check the result
pt = session.query(Point).one()
assert pt.id == 1
assert pt.three_d_geom.srid == 4326
assert pt.three_d_geom.desc.lower() == (
'01010000a0e6100000000000000000144000000000008046400000000000000000')
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Total running time of the script: ( 0 minutes 0.000 seconds)