GeoJSON Handle ID properly (NetTopologySuite#83)

Author: FObermaier

NetTopologySuite.IO/NetTopologySuite.IO.GeoJSON/Converters/AttributesTableConverter.cs

@@ -29,6 +29,9 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
             string[] names = attributes.GetNames();
             foreach (string name in names)
             {
+                // skip id
+                if (name == "id") continue;
+
                 writer.WritePropertyName(name);
                 object val = attributes[name];
                 serializer.Serialize(writer, val);

NetTopologySuite.IO/NetTopologySuite.IO.GeoJSON/Converters/FeatureConverter.cs

@@ -28,12 +28,28 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
                 return;
 
             writer.WriteStartObject();
+
+            // type
             writer.WritePropertyName("type");
             writer.WriteValue("Feature");
+            
+            // Add the id here if present in attributes.
+            // It will be skipped in serialization of properties
+            if (feature.Attributes.Exists("id"))
+            {
+                var id = feature.Attributes["id"];
+                writer.WritePropertyName("id");
+                serializer.Serialize(writer, id);
+            }
+
+            // geometry
             writer.WritePropertyName("geometry");
             serializer.Serialize(writer, feature.Geometry);
+
+            // properties
             writer.WritePropertyName("properties");
             serializer.Serialize(writer, feature.Attributes);
+
             writer.WriteEndObject();
         }
 

NetTopologySuite.IO/NetTopologySuite.IO.Tests/GeoJSON/GitHubIssues.cs

@@ -0,0 +1,54 @@
+using System.IO;
+using System.Text;
+using NetTopologySuite.Features;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using NUnit.Framework;
+
+namespace NetTopologySuite.IO.Tests.GeoJSON
+{
+    [Category("GitHub")]
+    [TestFixture]
+    public class GitHubIssues
+    {
+        [Test(Description = "Testcase for Issue 83") ]
+        public void TestIssue83()
+        {
+            var geoJson = "{ \"type\": \"Feature\", " + 
+                            "\"geometry\": { \"type\": \"Point\", \"coordinates\": [10.0, 60.0] }, " +
+                            "\"id\": 1, " +
+                            "\"properties\": { \"Name\": \"test\" } }";
+
+            var s = new GeoJsonSerializer();
+            Feature f = null;
+            Assert.DoesNotThrow( () =>
+                f = s.Deserialize<Feature>(new JsonTextReader(new StringReader(geoJson)))
+                ); 
+
+            Assert.IsNotNull(f, "f != null");
+            Assert.IsTrue(f.HasID(), "f.HasID()");
+            Assert.AreEqual(1, f.ID(), "f.ID != 1");
+
+            var sb = new StringBuilder();
+            var tw = new JsonTextWriter(new StringWriter(sb));
+            s.Serialize(tw, f);
+            var geoJsonRes = sb.ToString();
+            
+            CompareJson(geoJson, geoJsonRes);
+        }
+
+        public void CompareJson(string expectedJson, string json)
+        {
+            var e = JToken.Parse(expectedJson);
+            var j = JToken.Parse(json);
+
+            if (!JToken.DeepEquals(e, j))
+            {
+                var res = string.Format("The json's do not match:\n1: {0}\n2:{1}",
+                    expectedJson, json);
+                Assert.IsTrue(false, res);
+            }
+
+        }
+    }
+}

NetTopologySuite.IO/NetTopologySuite.IO.Tests/NetTopologySuite.IO.Tests.csproj

@@ -16,7 +16,6 @@
     <FileAlignment>512</FileAlignment>
     <TargetFrameworkProfile>Client</TargetFrameworkProfile>
     <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
-
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
@@ -84,6 +83,7 @@
     <Compile Include="GeoJSON\FeatureConverterTest.cs" />
     <Compile Include="GeoJSON\GeoJsonSerializerTest.cs" />
     <Compile Include="GeoJSON\GeoJsonWriterTest.cs" />
+    <Compile Include="GeoJSON\GitHubIssues.cs" />
     <Compile Include="GeoJSON\Issue148.cs" />
     <Compile Include="GeoJSON\Issue16Fixture.cs" />
     <Compile Include="GeoJSON\Issue32Fixture.cs" />

NetTopologySuite/Features/FeatureExtensions.cs

@@ -0,0 +1,48 @@
+using System;
+
+namespace NetTopologySuite.Features
+{
+    /// <summary>
+    /// Extension methods for <see cref="IFeature"/>s.
+    /// </summary>
+    public static class FeatureExtensions
+    {
+        static FeatureExtensions()
+        {
+            // According to GeoJSON name of the feature's identifier
+            IdAttributeName = "id";
+        }
+
+        /// <summary>
+        /// Gets or sets a name that is used to retrieve the ID of a feature from the attribute table
+        /// </summary>
+        public static string IdAttributeName { get; set; }
+
+        /// <summary>
+        /// Function to get a feature's ID
+        /// </summary>
+        /// <param name="feature">The feature</param>
+        /// <returns>The feature's ID if one has been assigned, otherwise <value>null</value></returns>
+        /// <exception cref="ArgumentNullException">Thrown, if <paramref name="feature"/> is <valu>null</valu></exception>
+        public static object ID(this IFeature feature)
+        {
+            return HasID(feature)
+                ? feature.Attributes[IdAttributeName]
+                : null;
+        }
+
+        /// <summary>
+        /// Function to evaluate if a feature has an ID
+        /// </summary>
+        /// <param name="feature">The feature</param>
+        /// <returns><value>true</value> if <paramref name="feature"/> has an identifier assigned, otherwise <value>false</value></returns>
+        /// <exception cref="ArgumentNullException">Thrown, if <paramref name="feature"/> is <valu>null</valu></exception>
+        public static bool HasID(this IFeature feature)
+        {
+            if (feature == null)
+                throw new ArgumentNullException("feature");
+
+            return feature.Attributes.Exists(IdAttributeName);
+        }
+    }
+}

NetTopologySuite/Features/IFeature.cs

@@ -2,10 +2,19 @@
 
 namespace NetTopologySuite.Features
 {
+    /// <summary>
+    /// Interface for feature classes
+    /// </summary>
     public interface IFeature
     {
+        /// <summary>
+        /// Gets or sets the attributes for the feature
+        /// </summary>
         IAttributesTable Attributes { get; set; }
 
+        /// <summary>
+        /// Gets or sets the feature's geometry
+        /// </summary>
         IGeometry Geometry { get; set; }
     }
 }

NetTopologySuite/NetTopologySuite.csproj

@@ -146,6 +146,7 @@
     <Compile Include="EdgeGraph\HalfEdge.cs" />
     <Compile Include="EdgeGraph\MarkHalfEdge.cs" />
     <Compile Include="Features\FeatureCollection.cs" />
+    <Compile Include="Features\FeatureExtensions.cs" />
     <Compile Include="Features\IFeature.cs" />
     <Compile Include="Geometries\Geometry.cs" />
     <Compile Include="Geometries\GeometryComponentFilter.cs" />

PortableClassLibrary/NetTopologySuite.Pcl/NetTopologySuite.Pcl.csproj

@@ -85,6 +85,9 @@
     <Compile Include="..\..\NetTopologySuite\Features\FeatureCollection.cs">
       <Link>Features\FeatureCollection.cs</Link>
     </Compile>
+    <Compile Include="..\..\NetTopologySuite\Features\FeatureExtensions.cs">
+      <Link>Features\FeatureExtensions.cs</Link>
+    </Compile>
     <Compile Include="..\..\NetTopologySuite\Features\IFeature.cs">
       <Link>Features\IFeature.cs</Link>
     </Compile>