polygon field added

README.md

@@ -126,6 +126,70 @@ point = {
     }
 serializer = PointFieldSerializer(data={'created': now, 'point': point})
 ```
+## PolygonField
+
+Polygon field for GeoDjango
+
+**Signature:** `PolygonField()`
+ - It takes a list of orderly pair arrays, representing points which all together are supposed to make a polygon. example:
+
+    A polygon without inner ring represented in 2d array format
+
+    [ 
+        [51.778564453125, 35.59925232772949], [50.1470947265625, 34.80929324176267],
+        [52.6080322265625, 34.492975402501536],[51.778564453125, 35.59925232772949] 
+    ]
+
+    The same polygon represented in 3d array format
+
+    [
+        [ 
+            [51.778564453125, 35.59925232772949], [50.1470947265625, 34.80929324176267],
+            [52.6080322265625, 34.492975402501536],[51.778564453125, 35.59925232772949] 
+        ]
+    ]
+
+    A polygon with inner ring (first element representing exterior and the second one interior ring)
+
+
+    [
+        [ [ 0 , 0 ] , [ 3 , 6 ] , [ 6 , 1 ] , [ 0 , 0 ] ], 
+        [ [ 2 , 2 ] , [ 3 , 3 ] , [ 4 , 2 ] , [ 2 , 2 ] ]   
+    ]
+
+
+**Example:**
+
+```python
+# serializer
+
+from drf_extra_fields.geo_fields import PolygonField
+
+class PolygonFieldSerializer(serializers.Serializer):
+    polygon = PolygonField(required=False)
+    created = serializers.DateTimeField()
+
+# use the serializer
+polygon = [
+        [
+            51.778564453125,
+            35.59925232772949
+        ],
+        [
+            50.1470947265625,
+            34.80929324176267
+        ],
+        [
+            52.6080322265625,
+            34.492975402501536
+        ],
+        [
+            51.778564453125,
+            35.59925232772949
+        ]
+    ]
+serializer = PolygonFieldSerializer(data={'created': now, 'polygon': polygon})
+```
 
 
 # RangeField

drf_extra_fields/geo_fields.py

@@ -1,21 +1,22 @@
 import json
-from django.contrib.gis.geos import GEOSGeometry
+from django.contrib.gis.geos import GEOSGeometry, polygon
 from django.contrib.gis.geos.error import GEOSException
 from django.utils.encoding import smart_str
 from django.utils.translation import gettext_lazy as _
 
 from rest_framework import serializers
 
 EMPTY_VALUES = (None, '', [], (), {})
+from django.contrib.gis.geos import Polygon 
 
 
 class PointField(serializers.Field):
     """
     A field for handling GeoDjango Point fields as a json format.
     Expected input format:
         {
-        "latitude": 49.8782482189424,
-         "longitude": 24.452545489
+            "latitude": 49.8782482189424,
+            "longitude": 24.452545489
         }
 
     """
@@ -76,3 +77,113 @@ def to_representation(self, value):
             value['latitude'] = smart_str(value.pop('latitude'))
 
         return value
+
+
+
+class PolygonField(serializers.Field):
+    """
+    A field for handling GeoDjango PolyGone fields as a array format.
+    Expected input format:
+        {
+            [
+                [
+                    51.778564453125,
+                    35.59925232772949
+                ],
+                [
+                    50.1470947265625,
+                    34.80929324176267
+                ],
+                [
+                    52.6080322265625,
+                    34.492975402501536
+                ],
+                [
+                    51.778564453125,
+                    35.59925232772949
+                ]
+            ]
+        }
+
+    """
+    type_name = 'PolygonField'
+    type_label = 'polygon'
+
+    default_error_messages = {
+        'invalid': _('Enter a valid polygon.'),
+    }
+
+    def __init__(self, *args, **kwargs):
+        super(PolygonField, self).__init__(*args, **kwargs)
+
+    def to_internal_value(self, value):
+        """
+        Parse array data and return a polygon object
+        """
+        if value in EMPTY_VALUES and not self.required:
+            return None
+
+
+        polygon_type = None
+
+        try:
+            new_value = []
+
+            if len(value)>2:
+                # a polygon without the ring in a 2-d array
+                for item in value:
+                    item = list(map(float, item))
+                    new_value.append(item)
+
+            elif len(value)==2:
+                # a polygon with inner ring
+                polygon_type = 'with_inner_ring'
+
+                for i in range(2):
+                    # a loop of 2 iterations. one per each ring
+                    ring_array = []
+                    for item in value[i]:
+                        item = list(map(float, item))
+                        ring_array.append(item)
+                    new_value.append(ring_array)
+
+            elif len(value)==1:
+                # a polygon without the ring in a 3-d array. not supported by django, should be converted to 2-d
+                for item in value[0]:
+                    item = list(map(float, item))
+                    new_value.append(item)
+
+        except ValueError as e:
+            print(e)
+            self.fail('invalid')
+
+        try:
+            if polygon_type=='with_inner_ring':
+                # for polygons with inner ring you should pass the exterior and interior ring seperated with comma to Polygon
+                return Polygon(new_value[0], new_value[1]) 
+
+            else:
+                return Polygon(new_value)
+
+        except (GEOSException, ValueError, TypeError) as e:
+            print(e)
+            print(new_value)
+            self.fail('invalid')
+
+
+
+    def to_representation(self, value):
+        """
+        Transform Polygon object to array of arrays.
+        """
+        if value is None:
+            return value
+
+        if isinstance(value, GEOSGeometry):
+            value = json.loads(value.geojson)['coordinates']
+
+
+        return {
+            'coordinates': value
+        }
+