Fix/id type support

src/JsonApiDotNetCore/Builders/DocumentBuilder.cs

@@ -94,7 +94,7 @@ private DocumentData _getData(ContextEntity contextEntity, IIdentifiable entity)
             var data = new DocumentData
             {
                 Type = contextEntity.EntityName,
-                Id = entity.Id.ToString()
+                Id = entity.StringId
             };
 
             if (_jsonApiContext.IsRelationshipData)
@@ -124,8 +124,8 @@ private void _addRelationships(DocumentData data, ContextEntity contextEntity, I
                 {
                     Links = new Links
                     {
-                        Self = linkBuilder.GetSelfRelationLink(contextEntity.EntityName, entity.Id.ToString(), r.InternalRelationshipName),
-                        Related = linkBuilder.GetRelatedRelationLink(contextEntity.EntityName, entity.Id.ToString(), r.InternalRelationshipName)
+                        Self = linkBuilder.GetSelfRelationLink(contextEntity.EntityName, entity.StringId, r.InternalRelationshipName),
+                        Related = linkBuilder.GetRelatedRelationLink(contextEntity.EntityName, entity.StringId, r.InternalRelationshipName)
                     }
                 };
 
@@ -175,7 +175,7 @@ private DocumentData _getIncludedEntity(IIdentifiable entity)
             var data = new DocumentData
             {
                 Type = contextEntity.EntityName,
-                Id = entity.Id.ToString()
+                Id = entity.StringId
             };
 
             data.Attributes = new Dictionary<string, object>();
@@ -205,7 +205,7 @@ private List<Dictionary<string, string>> _getRelationships(IEnumerable<object> e
             {
                 relationships.Add(new Dictionary<string, string> {
                     {"type", typeName.EntityName.Dasherize() },
-                    {"id", ((IIdentifiable)entity).Id.ToString() }
+                    {"id", ((IIdentifiable)entity).StringId }
                 });
             }
             return relationships;
@@ -218,7 +218,7 @@ private Dictionary<string, string> _getRelationship(object entity, string relati
 
             return new Dictionary<string, string> {
                     {"type", typeName.EntityName.Dasherize() },
-                    {"id", ((IIdentifiable)entity).Id.ToString() }
+                    {"id", ((IIdentifiable)entity).StringId }
                 };
         }
     }

src/JsonApiDotNetCore/Controllers/JsonApiController.cs

@@ -13,7 +13,7 @@
 
 namespace JsonApiDotNetCore.Controllers
 {
-    public class JsonApiController<T> 
+    public class JsonApiController<T>
     : JsonApiController<T, int> where T : class, IIdentifiable<int>
     {
         public JsonApiController(
@@ -24,7 +24,7 @@ public JsonApiController(
         { }
     }
 
-    public class JsonApiController<T, TId> 
+    public class JsonApiController<T, TId>
     : JsonApiControllerMixin where T : class, IIdentifiable<TId>
     {
         private readonly IEntityRepository<T, TId> _entities;
@@ -77,7 +77,7 @@ public virtual async Task<IActionResult> GetAsync()
         public virtual async Task<IActionResult> GetAsync(TId id)
         {
             T entity;
-            if(_jsonApiContext.QuerySet?.IncludedRelationships != null)
+            if (_jsonApiContext.QuerySet?.IncludedRelationships != null)
                 entity = await _getWithRelationshipsAsync(id);
             else
                 entity = await _entities.GetAsync(id);
@@ -138,8 +138,7 @@ public virtual async Task<IActionResult> PostAsync([FromBody] T entity)
                 return UnprocessableEntity();
             }
 
-            var stringId = entity.Id.ToString();
-            if(stringId.Length > 0 && stringId != "0")
+            if (!string.IsNullOrEmpty(entity.StringId))
                 return Forbidden();
 
             await _entities.CreateAsync(entity);
@@ -158,7 +157,7 @@ public virtual async Task<IActionResult> PatchAsync(TId id, [FromBody] T entity)
 
             var updatedEntity = await _entities.UpdateAsync(id, entity);
 
-            if(updatedEntity == null)  return NotFound();
+            if (updatedEntity == null) return NotFound();
 
             return Ok(updatedEntity);
         }
@@ -185,12 +184,12 @@ public virtual async Task<IActionResult> PatchRelationshipsAsync(TId id, string
                 .Relationships
                 .FirstOrDefault(r => r.InternalRelationshipName == relationshipName);
 
-            var relationshipIds = relationships.Select(r=>r.Id);
-            
+            var relationshipIds = relationships.Select(r => r.Id);
+
             await _entities.UpdateRelationshipsAsync(entity, relationship, relationshipIds);
 
             return Ok();
-            
+
         }
 
         [HttpDelete("{id}")]
@@ -208,14 +207,14 @@ private IQueryable<T> ApplySortAndFilterQuery(IQueryable<T> entities)
         {
             var query = _jsonApiContext.QuerySet;
 
-            if(_jsonApiContext.QuerySet == null)
+            if (_jsonApiContext.QuerySet == null)
                 return entities;
 
-            if(query.Filters.Count > 0)
-                foreach(var filter in query.Filters)
+            if (query.Filters.Count > 0)
+                foreach (var filter in query.Filters)
                     entities = _entities.Filter(entities, filter);
 
-            if(query.SortParameters != null && query.SortParameters.Count > 0)
+            if (query.SortParameters != null && query.SortParameters.Count > 0)
                 entities = _entities.Sort(entities, query.SortParameters);
 
             return entities;
@@ -224,7 +223,7 @@ private IQueryable<T> ApplySortAndFilterQuery(IQueryable<T> entities)
         private async Task<IEnumerable<T>> ApplyPageQueryAsync(IQueryable<T> entities)
         {
             var pageManager = _jsonApiContext.PageManager;
-            if(!pageManager.IsPaginated)
+            if (!pageManager.IsPaginated)
                 return entities;
 
             var query = _jsonApiContext.QuerySet?.PageQuery ?? new PageQuery();
@@ -238,7 +237,7 @@ private IQueryable<T> IncludeRelationships(IQueryable<T> entities, List<string>
         {
             _jsonApiContext.IncludedRelationships = relationships;
 
-            foreach(var r in relationships)
+            foreach (var r in relationships)
                 entities = _entities.Include(entities, r.ToProperCase());
 
             return entities;

src/JsonApiDotNetCore/Internal/Generics/GenericProcessor.cs

@@ -1,7 +1,5 @@
-using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
-using System.Reflection;
 using System.Threading.Tasks;
 using JsonApiDotNetCore.Extensions;
 using JsonApiDotNetCore.Models;
@@ -18,21 +16,26 @@ public GenericProcessor(DbContext context)
         }
 
         public async Task UpdateRelationshipsAsync(object parent, RelationshipAttribute relationship, IEnumerable<string> relationshipIds)
+        {
+            SetRelationships(parent, relationship, relationshipIds);
+
+            await _context.SaveChangesAsync();
+        }
+
+        public void SetRelationships(object parent, RelationshipAttribute relationship, IEnumerable<string> relationshipIds)
         {
             var relationshipType = relationship.Type;
 
-            if(relationship.IsHasMany)
+            if (relationship.IsHasMany)
             {
-                var entities = _context.GetDbSet<T>().Where(x => relationshipIds.Contains(x.Id.ToString())).ToList();
+                var entities = _context.GetDbSet<T>().Where(x => relationshipIds.Contains(x.StringId)).ToList();
                 relationship.SetValue(parent, entities);
             }
             else
             {
-                var entity = _context.GetDbSet<T>().SingleOrDefault(x => relationshipIds.First() == x.Id.ToString());
+                var entity = _context.GetDbSet<T>().SingleOrDefault(x => relationshipIds.First() == x.StringId);
                 relationship.SetValue(parent, entity);
-            }            
-
-            await _context.SaveChangesAsync();
+            }
         }
     }
 }

src/JsonApiDotNetCore/Internal/Generics/IGenericProcessor.cs

@@ -7,5 +7,6 @@ namespace JsonApiDotNetCore.Internal
     public interface IGenericProcessor
     {
         Task UpdateRelationshipsAsync(object parent, RelationshipAttribute relationship, IEnumerable<string> relationshipIds);
+        void SetRelationships(object parent, RelationshipAttribute relationship, IEnumerable<string> relationshipIds);
     }
 }

src/JsonApiDotNetCore/Internal/TypeHelper.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Reflection;
+
+namespace JsonApiDotNetCore.Internal
+{
+    public static class TypeHelper
+    {
+        public static object ConvertType(object value, Type type)
+        {
+            if(value == null)
+                return null;
+
+            if (type.GetTypeInfo().IsGenericType && type.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
+                type = Nullable.GetUnderlyingType(type);            
+
+            var stringValue = value.ToString();
+
+            if(type == typeof(Guid))
+                return Guid.Parse(stringValue);
+
+            return Convert.ChangeType(stringValue, type);
+        }
+    }
+}

src/JsonApiDotNetCore/Models/IIdentifiable.cs

@@ -2,11 +2,11 @@ namespace JsonApiDotNetCore.Models
 {
     public interface IIdentifiable
     {
-        object Id { get; set; }
+        string StringId { get; set; }
     }
 
     public interface IIdentifiable<T> : IIdentifiable
     {
-        new T Id { get; set; }
+        T Id { get; set; }
     }
 }

src/JsonApiDotNetCore/Models/Identifiable.cs

@@ -1,3 +1,7 @@
+using System;
+using System.ComponentModel.DataAnnotations.Schema;
+using JsonApiDotNetCore.Internal;
+
 namespace JsonApiDotNetCore.Models
 {
     public class Identifiable : Identifiable<int>
@@ -7,10 +11,32 @@ public class Identifiable<T> : IIdentifiable<T>, IIdentifiable
     {
         public virtual T Id { get; set; }
 
-        object IIdentifiable.Id
+        [NotMapped]
+        public string StringId
+        {
+            get { return GetStringId(Id); }
+            set { Id = (T)GetConcreteId(value); }
+        }
+
+        protected virtual string GetStringId(object value)
+        {
+            var type = typeof(T);
+            var stringValue = value.ToString();
+
+            if(type == typeof(Guid))
+            {
+                var guid = Guid.Parse(stringValue);
+                return (guid == Guid.Empty ? string.Empty : stringValue);
+            }
+
+            if(stringValue == "0") return string.Empty;
+
+            return stringValue;
+        }
+
+        protected virtual object GetConcreteId(string value)
         {
-            get { return Id; }
-            set { Id = (T)value; }
+            return TypeHelper.ConvertType(value, typeof(T));
         }
     }
 }