Allow "foreign members" in a GeoJSON Objects

README.md

@@ -10,6 +10,7 @@ This library contains:
 
 - Functions for encoding and decoding GeoJSON formatted data
 - Classes for all GeoJSON Objects
+- Allow "foreign members" in a GeoJSON Objects
 
 ## Installation
 
@@ -388,6 +389,34 @@ feature_collection.to_json
 }
 ```
 
+## Foreign Members
+
+For example, in the `Pont` object shown below
+
+```json
+{
+  "type": "Point",
+  "coordinates": [-80.1347334, 25.7663562],
+  "title": "Example Point"
+}
+```
+
+the name/value pair of `"title": "Example Point"` is a foreign member.
+
+GeoJSON semantics do not apply to foreign members and their descendants, regardless of their names and values.
+
+If the GeoJSON type include foreign members, this properties in the JSON document will be stored in a `Hash(String, JSON::Any)`.
+On serialization, any keys inside `json_unmapped` will be serialized and appended to the current json object.
+
+```crystal
+point = GeoJSON::Point.new([-80.1347334, 25.7663562])
+
+json_unmapped = Hash(String, JSON::Any).new
+json_unmapped["title"] = JSON::Any.new("Example Point")
+
+point.json_unmapped = json_unmapped
+```
+
 ## Contributing
 
 1. Fork it (<https://github.com/geocrystal/geo_json/fork>)

spec/feature_spec.cr

@@ -39,6 +39,18 @@ describe GeoJSON::Feature do
     },
   }.to_json
 
+  feature_with_foreign_members_json = {
+    "type"     => "Feature",
+    "geometry" => {
+      "type"        => "Point",
+      "coordinates" => point_coordinates,
+    },
+    "properties" => {
+      "prop0" => "value0",
+    },
+    "title" => "Example Feature",
+  }.to_json
+
   describe "json parser" do
     it "parses feture point json" do
       feature = GeoJSON::Feature.from_json(feature_point_json)
@@ -55,6 +67,15 @@ describe GeoJSON::Feature do
       polygon = feature.geometry.not_nil!.as(GeoJSON::Polygon)
       polygon.coordinates.should be_a(Array(Array(GeoJSON::Coordinates)))
     end
+
+    it "parses feture with foreign json member" do
+      feature = GeoJSON::Feature.from_json(feature_with_foreign_members_json)
+
+      feature.should be_a(GeoJSON::Feature)
+      feature.type.should eq("Feature")
+      feature.json_unmapped["title"].should eq("Example Feature")
+      feature.geometry.should be_a(GeoJSON::Point)
+    end
   end
 
   describe ".new" do
@@ -86,6 +107,20 @@ describe GeoJSON::Feature do
       feature.properties.should eq(properties)
       feature.id.should eq(1)
     end
+
+    it "initialize Feature with foreign member" do
+      geometry = GeoJSON::Point.new(point_coordinates)
+      properties = {"prop0" => "value0"} of String => JSON::Any::Type
+
+      json_unmapped = Hash(String, JSON::Any).new
+      json_unmapped["title"] = JSON::Any.new("Example Feature")
+
+      feature = GeoJSON::Feature.new(geometry, properties)
+      feature.json_unmapped = json_unmapped
+
+      feature.geometry.should eq(geometry)
+      feature.to_json.should eq(feature_with_foreign_members_json)
+    end
   end
 
   describe "json object" do

spec/multi_polygon_spec.cr

@@ -45,7 +45,6 @@ describe GeoJSON::MultiPolygon do
       polygon2 = GeoJSON::Polygon.new(ring2)
 
       multi_polygon = GeoJSON::MultiPolygon.new([polygon1, polygon2])
-      puts multi_polygon.to_json
 
       multi_polygon.should be_a(GeoJSON::MultiPolygon)
       multi_polygon.type.should eq("MultiPolygon")

spec/point_spec.cr

@@ -90,6 +90,17 @@ describe GeoJSON::Point do
       point.to_json.should eq(point_json)
     end
 
+    it "creates Point with foreign member" do
+      point = GeoJSON::Point.new(position)
+
+      json_unmapped = Hash(String, JSON::Any).new
+      json_unmapped["title"] = JSON::Any.new("Example Point")
+
+      point.json_unmapped = json_unmapped
+
+      point.to_json.should eq("{\"type\":\"Point\",\"coordinates\":[-80.1347334,25.7663562],\"title\":\"Example Point\"}")
+    end
+
     it "raises an exception if coordinates are invalid" do
       expect_raises GeoJSON::Exception, "coordinates need to have have two or three elements" do
         GeoJSON::Point.new(invalid_position)

src/geo_json/object.cr

@@ -13,6 +13,7 @@ module GeoJSON
   # * A GeoJSON object MAY have other members
   abstract class Object
     include JSON::Serializable
+    include JSON::Serializable::Unmapped
 
     # All possible GeoJSON types.
     alias Type = Point | MultiPoint | LineString | MultiLineString | Polygon | MultiPolygon