doc(Identifiable): add xml docs

src/JsonApiDotNetCore/Models/Identifiable.cs

@@ -5,35 +5,55 @@
 namespace JsonApiDotNetCore.Models
 {
     public class Identifiable : Identifiable<int>
-    {}
-    
+    { }
+
     public class Identifiable<T> : IIdentifiable<T>
     {
+        /// <summary>
+        /// The resource identifier
+        /// </summary>
         public virtual T Id { get; set; }
 
+        /// <summary>
+        /// The string representation of the `Id`.
+        /// 
+        /// This is used in serialization and deserialization.
+        /// The getters should handle the conversion
+        /// from `typeof(T)` to a string and the setter vice versa.
+        /// 
+        /// To override this behavior, you can either implement the
+        /// <see cref="IIdentifiable{T}"> interface directly or override
+        /// `GetStringId` and `GetTypedId` methods.
+        /// </summary>
         [NotMapped]
         public string StringId
         {
             get => GetStringId(Id);
             set => Id = GetTypedId(value);
         }
 
+        /// <summary>
+        /// Convert the provided resource identifier to a string.
+        /// </summary>
         protected virtual string GetStringId(object value)
         {
             var type = typeof(T);
             var stringValue = value.ToString();
 
-            if(type == typeof(Guid))
+            if (type == typeof(Guid))
             {
                 var guid = Guid.Parse(stringValue);
                 return guid == Guid.Empty ? string.Empty : stringValue;
             }
 
-            return stringValue == "0" 
-                ? string.Empty 
+            return stringValue == "0"
+                ? string.Empty
                 : stringValue;
         }
 
+        /// <summary>
+        /// Convert a string to a typed resource identifier.
+        /// </summary>
         protected virtual T GetTypedId(string value)
         {
             var convertedValue = TypeHelper.ConvertType(value, typeof(T));