1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
|
DSE Geometry Types
==================
This section shows how to query and work with the geometric types provided by DSE.
These types are enabled implicitly by creating the Session from :class:`cassandra.cluster.Cluster`.
This module implicitly registers these types for use in the driver. This extension provides
some simple representative types in :mod:`cassandra.util` for inserting and retrieving data::
from cassandra.cluster import Cluster
from cassandra.util import Point, LineString, Polygon
session = Cluster().connect()
session.execute("INSERT INTO ks.geo (k, point, line, poly) VALUES (%s, %s, %s, %s)",
0, Point(1, 2), LineString(((1, 2), (3, 4))), Polygon(((1, 2), (3, 4), (5, 6))))
Queries returning geometric types return the :mod:`dse.util` types. Note that these can easily be used to construct
types from third-party libraries using the common attributes::
from shapely.geometry import LineString
shapely_linestrings = [LineString(res.line.coords) for res in session.execute("SELECT line FROM ks.geo")]
For prepared statements, shapely geometry types can be used interchangeably with the built-in types because their
defining attributes are the same::
from shapely.geometry import Point
prepared = session.prepare("UPDATE ks.geo SET point = ? WHERE k = ?")
session.execute(prepared, (0, Point(1.2, 3.4)))
In order to use shapely types in a CQL-interpolated (non-prepared) query, one must update the encoder with those types, specifying
the same string encoder as set for the internal types::
from cassandra import util
from shapely.geometry import Point, LineString, Polygon
encoder_func = session.encoder.mapping[util.Point]
for t in (Point, LineString, Polygon):
session.encoder.mapping[t] = encoder_func
session.execute("UPDATE ks.geo SET point = %s where k = %s", (0, Point(1.2, 3.4)))
|
