Add helper to dump geojson to string

Author: yohanboniface

README.md

@@ -22,9 +22,32 @@ You need to register the extension:
     import postgis
     postgis.register(mydatabase.get_cursor())
 
-Then you can pass geoms to psycopg:
+Then you can pass and get geoms using psycopg:
 
     cursor.execute('INSERT INTO table (geom) VALUES (%s)', [Point(x=1, y=2, srid=4326)])
     cursor.execute('SELECT geom FROM points LIMIT 1')
     geom = cursor.fetchone()[0]
     assert geom.coords == (1, 2)
+
+
+## Example
+
+    > import psycopg2
+    > from postgis import register, LineString
+    > db = psycopg2.connect(dbname="test")
+    > cursor = db.cursor()
+    > register(cursor)
+    > cursor.execute('CREATE TABLE IF NOT EXISTS mytable ("geom" geometry(LineString) NOT NULL)')
+    > cursor.execute('INSERT INTO mytable (geom) VALUES (%s)', [LineString([(1, 2), (3, 4)], srid=4326)])
+    > cursor.execute('SELECT geom FROM mytable LIMIT 1')
+    > geom = cursor.fetchone()[0]
+    > geom
+    <LineString LINESTRING(1.0 2.0, 3.0 4.0)>
+    > geom[0]
+    <Point POINT(1.0 2.0)>
+    > geom.coords
+    ((1.0, 2.0), (3.0, 4.0))
+    > geom.geojson
+    {'coordinates': ((1.0, 2.0), (3.0, 4.0)), 'type': 'LineString'}
+    > str(geom.geojson)
+    '{"type": "LineString", "coordinates": [[1, 2], [3, 4]]}'

postgis/geojson.py

@@ -0,0 +1,7 @@
+import json
+
+
+class GeoJSON(dict):
+
+    def __str__(self):
+        return json.dumps(self)

postgis/geometry.py

@@ -1,5 +1,6 @@
 from psycopg2 import extensions as _ext
 from .reader import EWKBReader, Typed
+from .geojson import GeoJSON
 
 
 class Geometry(object, metaclass=Typed):
@@ -50,10 +51,10 @@ def wkt(self):
 
     @property
     def geojson(self):
-        return {
+        return GeoJSON({
             'type': self.name,
             'coordinates': self.coords
-        }
+        })
 
 
 def register(cursor):

postgis/geometrycollection.py

@@ -1,4 +1,5 @@
 from .geometry import Geometry
+from .geojson import GeoJSON
 
 
 class GeometryCollection(Geometry):
@@ -42,7 +43,7 @@ def wkt_coords(self):
 
     @property
     def geojson(self):
-        return {
+        return GeoJSON({
             'type': self.name,
             'geometries': [g.geojson for g in self]
-        }
+        })

tests/test_linestring.py

@@ -20,6 +20,13 @@ def test_linestring_geojson():
                             "coordinates": ((1, 2), (3, 4))}
 
 
+def test_linestring_geojson_as_string():
+    line = LineString(((1, 2), (3, 4)))
+    geojson = str(line.geojson)
+    assert '"type": "LineString"' in geojson
+    assert '"coordinates": [[1, 2], [3, 4]]' in geojson
+
+
 def test_geom_should_compare_with_coords():
     assert ((30, 10), (10, 30), (40, 40)) == LineString(((30, 10), (10, 30), (40, 40)))  # noqa
 

tests/test_point.py

@@ -20,6 +20,13 @@ def test_point_geojson():
     assert point.geojson == {"type": "Point", "coordinates": (1, 2)}
 
 
+def test_point_geojson_as_string():
+    point = Point(1, 2)
+    geojson = str(point.geojson)
+    assert '"type": "Point"' in geojson
+    assert '"coordinates": [1, 2]' in geojson
+
+
 def test_point_should_compare_with_coords():
     assert (-1.123456789, 2.987654321) == Point(-1.123456789, 2.987654321)