Add support for nested GeometryCollection with warnings.

Closes #110.

geojson_pydantic/geometries.py

@@ -1,5 +1,8 @@
 """pydantic models for GeoJSON Geometry objects."""
+from __future__ import annotations
+
 import abc
+import warnings
 from typing import Any, Iterator, List, Literal, Optional, Protocol, Union
 
 from pydantic import BaseModel, Field, ValidationError, validator
@@ -241,18 +244,18 @@ class GeometryCollection(BaseModel, GeoInterfaceMixin):
     """GeometryCollection Model"""
 
     type: Literal["GeometryCollection"]
-    geometries: List[Geometry]
+    geometries: List[Union[Geometry, GeometryCollection]]
     bbox: Optional[BBox] = None
 
-    def __iter__(self) -> Iterator[Geometry]:  # type: ignore [override]
+    def __iter__(self) -> Iterator[Union[Geometry, GeometryCollection]]:  # type: ignore [override]
         """iterate over geometries"""
         return iter(self.geometries)
 
     def __len__(self) -> int:
         """return geometries length"""
         return len(self.geometries)
 
-    def __getitem__(self, index: int) -> Geometry:
+    def __getitem__(self, index: int) -> Union[Geometry, GeometryCollection]:
         """get geometry at a given index"""
         return self.geometries[index]
 
@@ -274,6 +277,23 @@ def wkt(self) -> str:
         z = " Z " if "Z" in geometries else " "
         return f"{self.type.upper()}{z}{geometries}"
 
+    @validator("geometries")
+    def check_geometries(cls, geometries: List) -> List:
+        """Add warnings for conditions the spec does not explicitly forbid."""
+        if len(geometries) == 1:
+            warnings.warn(
+                "GeometryCollection should not be used for single geometries."
+            )
+        if any(geom.type == "GeometryCollection" for geom in geometries):
+            warnings.warn(
+                "GeometryCollection should not be used for nested GeometryCollections."
+            )
+        if len(set(geom.type for geom in geometries)) == 1:
+            warnings.warn(
+                "GeometryCollection should not be used for homogeneous collections."
+            )
+        return geometries
+
 
 def parse_geometry_obj(obj: Any) -> Geometry:
     """

tests/test_features.py

@@ -26,22 +26,29 @@ class GenericProperties(BaseModel):
     "size": randint(0, 1000),
 }
 
+coordinates = [
+    [
+        [13.38272, 52.46385],
+        [13.42786, 52.46385],
+        [13.42786, 52.48445],
+        [13.38272, 52.48445],
+        [13.38272, 52.46385],
+    ]
+]
+
 polygon: Dict[str, Any] = {
     "type": "Polygon",
-    "coordinates": [
-        [
-            [13.38272, 52.46385],
-            [13.42786, 52.46385],
-            [13.42786, 52.48445],
-            [13.38272, 52.48445],
-            [13.38272, 52.46385],
-        ]
-    ],
+    "coordinates": coordinates,
+}
+
+multipolygon: Dict[str, Any] = {
+    "type": "MultiPolygon",
+    "coordinates": [coordinates],
 }
 
 geom_collection: Dict[str, Any] = {
     "type": "GeometryCollection",
-    "geometries": [polygon, polygon],
+    "geometries": [polygon, multipolygon],
 }
 
 test_feature: Dict[str, Any] = {
@@ -131,7 +138,6 @@ def test_generic_geometry_collection():
     assert feature.properties.id == test_feature_geometry_collection["properties"]["id"]
     assert type(feature.geometry) == GeometryCollection
     assert feature.geometry.wkt.startswith("GEOMETRYCOLLECTION (POLYGON ")
-    assert feature.geometry.geometries[0].wkt == feature.geometry.geometries[1].wkt
     assert type(feature.properties) == GenericProperties
     assert hasattr(feature.properties, "id")
 

tests/test_geometries.py

@@ -452,33 +452,42 @@ def test_parse_geometry_obj_invalid_point():
 def test_geometry_collection_iteration(coordinates):
     """test if geometry collection is iterable"""
     polygon = Polygon(type="Polygon", coordinates=coordinates)
-    gc = GeometryCollection(type="GeometryCollection", geometries=[polygon, polygon])
+    multipolygon = MultiPolygon(type="MultiPolygon", coordinates=[coordinates])
+    gc = GeometryCollection(
+        type="GeometryCollection", geometries=[polygon, multipolygon]
+    )
     assert hasattr(gc, "__geo_interface__")
     assert_wkt_equivalence(gc)
     iter(gc)
 
 
 @pytest.mark.parametrize(
-    "polygon", [[[(1.0, 2.0), (3.0, 4.0), (5.0, 6.0), (1.0, 2.0)]]]
+    "coordinates", [[[(1.0, 2.0), (3.0, 4.0), (5.0, 6.0), (1.0, 2.0)]]]
 )
-def test_len_geometry_collection(polygon):
+def test_len_geometry_collection(coordinates):
     """test if GeometryCollection return self leng"""
-    polygon = Polygon(type="Polygon", coordinates=polygon)
-    gc = GeometryCollection(type="GeometryCollection", geometries=[polygon, polygon])
+    polygon = Polygon(type="Polygon", coordinates=coordinates)
+    multipolygon = MultiPolygon(type="MultiPolygon", coordinates=[coordinates])
+    gc = GeometryCollection(
+        type="GeometryCollection", geometries=[polygon, multipolygon]
+    )
     assert_wkt_equivalence(gc)
     assert len(gc) == 2
 
 
 @pytest.mark.parametrize(
-    "polygon", [[[(1.0, 2.0), (3.0, 4.0), (5.0, 6.0), (1.0, 2.0)]]]
+    "coordinates", [[[(1.0, 2.0), (3.0, 4.0), (5.0, 6.0), (1.0, 2.0)]]]
 )
-def test_getitem_geometry_collection(polygon):
-    """test if GeometryCollection return self leng"""
-    polygon = Polygon(type="Polygon", coordinates=polygon)
-    gc = GeometryCollection(type="GeometryCollection", geometries=[polygon, polygon])
+def test_getitem_geometry_collection(coordinates):
+    """test if GeometryCollection is subscriptable"""
+    polygon = Polygon(type="Polygon", coordinates=coordinates)
+    multipolygon = MultiPolygon(type="MultiPolygon", coordinates=[coordinates])
+    gc = GeometryCollection(
+        type="GeometryCollection", geometries=[polygon, multipolygon]
+    )
     assert_wkt_equivalence(gc)
-    item = gc[0]
-    assert item == gc[0]
+    assert polygon == gc[0]
+    assert multipolygon == gc[1]
 
 
 def test_wkt_mixed_geometry_collection():