feat: JSON ref responses

playground/Coalesce.Web.Vue3/src/components/test.vue

@@ -12,6 +12,7 @@
               density="compact"
               class="my-4"
               error-messages="sdfsdf"
+              :params="{useRef: true}"
             >
             </c-select>
           </v-col>
@@ -163,6 +164,7 @@ export default class Test extends Base {
     this.personList.$params.noCount = true;
     this.personList.$load();
 
+    this.caseVm.$params.useRef = true;
     await this.caseVm.$load(15);
     await this.caseVm.downloadImage();
     await this.company.$load(1);

src/IntelliTect.Coalesce/Api/Controllers/ApiActionFilter.cs

@@ -2,19 +2,23 @@
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.Mvc.Filters;
+using Microsoft.AspNetCore.Mvc.Formatters;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Migrations;
 using Microsoft.EntityFrameworkCore.Storage;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using Microsoft.Net.Http.Headers;
 using System;
 using System.Collections.Generic;
 using System.Data.Common;
 using System.Linq;
 using System.Net;
 using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 
 namespace IntelliTect.Coalesce.Api.Controllers
 {
@@ -113,15 +117,33 @@ public virtual void OnActionExecuted(ActionExecutedContext context)
                 }
             }
 
-            if (response.StatusCode == (int)HttpStatusCode.OK
-                && context.Result is ObjectResult result
-                && result.Value is ApiResult apiResult
-                && !apiResult.WasSuccessful
-            )
+            if (context.Result is ObjectResult result)
             {
-                result.StatusCode = 
-                response.StatusCode = 
-                    (int)HttpStatusCode.BadRequest;
+                var refHeader = new MediaTypeHeaderValue("application/json+ref");
+                if (context.HttpContext.Request.GetTypedHeaders().Accept.Any(h => h.IsSubsetOf(refHeader)))
+                {
+                    var jsonOptions = context.HttpContext.RequestServices.GetService<IOptions<JsonOptions>>()?.Value ?? new JsonOptions
+                    {
+                        JsonSerializerOptions =
+                        {
+                            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+                        }
+                    };
+                    var newOptions = new JsonSerializerOptions(jsonOptions.JsonSerializerOptions)
+                    {
+                        ReferenceHandler = new CoalesceJsonReferenceHandler()
+                    };
+                    result.Formatters.Add(new SystemTextJsonOutputFormatter(newOptions));
+                }
+
+                if (response.StatusCode == (int)HttpStatusCode.OK && 
+                    result.Value is ApiResult apiResult && 
+                    !apiResult.WasSuccessful)
+                {
+                    result.StatusCode =
+                    response.StatusCode =
+                        (int)HttpStatusCode.BadRequest;
+                }
             }
         }
 

src/IntelliTect.Coalesce/Api/Controllers/CoalesceJsonReferenceHandler.cs

@@ -0,0 +1,62 @@
+using IntelliTect.Coalesce.Models;
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Text.Json.Serialization;
+
+namespace IntelliTect.Coalesce.Api.Controllers;
+
+
+internal sealed class CoalesceJsonReferenceHandler : ReferenceHandler
+{
+    public override ReferenceResolver CreateResolver() => new PreserveReferenceResolver();
+
+    /// <summary>
+    /// From https://source.dot.net/#System.Text.Json/System/Text/Json/Serialization/PreserveReferenceResolver.cs
+    /// Same as the normal reference handler, but doesn't make refs for the root <see cref="ApiResult"/>,
+    /// nor for any <see cref="ICollection"/>s because collections will never be duplicated in Coalesce responses.
+    /// </summary>
+    internal sealed class PreserveReferenceResolver : ReferenceResolver
+    {
+        private uint _referenceCount;
+        private readonly Dictionary<object, string>? _objectToReferenceIdMap;
+
+        public PreserveReferenceResolver()
+        {
+            _objectToReferenceIdMap = new Dictionary<object, string>(ReferenceEqualityComparer.Instance);
+        }
+
+        public override void AddReference(string referenceId, object value)
+            => throw new NotSupportedException();
+
+        public override string GetReference(object value, out bool alreadyExists)
+        {
+            Debug.Assert(_objectToReferenceIdMap != null);
+            if (value is ApiResult || value is ICollection)
+            {
+                // Don't produce refs for the root response object,
+                // nor for collections (collections will never be duplicated)
+                alreadyExists = false;
+                return null!;
+            }
+
+            if (_objectToReferenceIdMap.TryGetValue(value, out string? referenceId))
+            {
+                alreadyExists = true;
+            }
+            else
+            {
+                _referenceCount++;
+                referenceId = _referenceCount.ToString();
+                _objectToReferenceIdMap.Add(value, referenceId);
+                alreadyExists = false;
+            }
+
+            return referenceId;
+        }
+
+        public override object ResolveReference(string referenceId)
+            => throw new NotSupportedException();
+    }
+}

src/IntelliTect.Coalesce/Mapping/IMappingContext.cs

@@ -8,15 +8,15 @@ namespace IntelliTect.Coalesce
     public interface IMappingContext
     {
         string? Includes { get; }
-        Dictionary<object, object> MappedObjects { get; }
         ClaimsPrincipal User { get; }
 
         bool IsInRoleCached(string role);
 
-        void AddMapping(object sourceObject, object mappedObject);
+        void AddMapping(object sourceObject, IncludeTree? includeTree, object mappedObject);
 
         bool TryGetMapping<TDto>(
             object sourceObject,
+            IncludeTree? includeTree,
             [System.Diagnostics.CodeAnalysis.NotNullWhen(true)]
             out TDto? mappedObject
         )

src/IntelliTect.Coalesce/Mapping/Mapper.cs

@@ -13,12 +13,11 @@ public static class Mapper
         {
             if (obj == null) return default;
 
-            // See if the object is already created, but only if we aren't restricting by an includes tree.
-            // If we do have an IncludeTree, we know the exact structure of our return data, so we don't need to worry about circular refs.
-            if (tree == null && context.TryGetMapping(obj, out TDto? existing)) return existing;
+            // See if we already mapped this object:
+            if (context.TryGetMapping(obj, tree, out TDto? existing)) return existing;
 
             var dto = new TDto();
-            if (tree == null) context.AddMapping(obj, dto);
+            context.AddMapping(obj, tree, dto);
 
             dto.MapFrom(obj, context, tree);
 

src/IntelliTect.Coalesce/Mapping/MappingContext.cs

@@ -16,8 +16,7 @@ public class MappingContext : IMappingContext
 
         public IServiceProvider? Services { get; }
 
-        public Dictionary<object, object> MappedObjects { get; } = new();
-
+        private Dictionary<(object, IncludeTree?, Type), object> _mappedObjects { get; } = new();
         private Dictionary<string, bool>? _roleCache;
         private Dictionary<Type, IPropertyRestriction>? _restrictionCache;
 
@@ -43,19 +42,20 @@ public bool IsInRoleCached(string role)
             return _roleCache[role] = User?.IsInRole(role) ?? false;
         }
 
-        public void AddMapping(object sourceObject, object mappedObject)
+        public void AddMapping(object sourceObject, IncludeTree? includeTree, object mappedObject)
         {
-            MappedObjects[sourceObject] = mappedObject;
+            _mappedObjects[(sourceObject, includeTree, mappedObject.GetType())] = mappedObject;
         }
 
         public bool TryGetMapping<TDto>(
             object sourceObject,
+            IncludeTree? includeTree,
             [System.Diagnostics.CodeAnalysis.NotNullWhen(true)]
             out TDto? mappedObject
         )
             where TDto : class
         {
-            if (!MappedObjects.TryGetValue(sourceObject, out object? existingMapped) || existingMapped is not TDto)
+            if (!_mappedObjects.TryGetValue((sourceObject, includeTree, typeof(TDto)), out object? existingMapped))
             {
                 mappedObject = default;
                 return false; 

src/coalesce-vue/src/api-client.ts

@@ -86,11 +86,18 @@ export interface DataSourceParameters {
    * Classes are found in `models.g.ts` as `<ModelName>.DataSources.<DataSourceName>`, e.g. `Person.DataSources.WithRelations`.
    */
   dataSource?: DataSource<DataSourceType> | null;
+
+  /** If true, request that the server use System.Text.Json reference preservation handling when serializing the response,
+   * which can significantly reduce the size of the response payload. This will also cause the resulting
+   * `Model` and `ViewModel` instances on the client to be deduplicated.
+   */
+  useRef?: boolean;
 }
 export class DataSourceParameters {
   constructor() {
     this.includes = null;
     this.dataSource = null;
+    this.useRef = false;
   }
 }
 
@@ -753,12 +760,22 @@ export class ApiClient<T extends ApiRoutedType> {
       query = mappedParams;
     }
 
+    let headers = config?.headers;
+    if (standardParameters?.useRef) {
+      headers = {
+        ...config?.headers,
+        Accept: standardParameters?.useRef
+          ? ["application/json+ref", "application/json"]
+          : ["application/json"],
+      };
+    }
     const axiosRequest = <AxiosRequestConfig>{
       method: method.httpMethod,
       url: url,
       data: body,
       responseType: method.return.type == "file" ? "blob" : "json",
       cancelToken: this._cancelToken,
+      headers,
       ...config,
       params: {
         ...query,

src/coalesce-vue/src/model.ts

@@ -250,6 +250,7 @@ export function parseValue(
 
 class ModelConversionVisitor extends Visitor<any, any[] | null, any | null> {
   private objects = new Map<object, object>();
+  private refs = new Map<object, object>();
 
   public override visitValue(value: any, meta: Value): any {
     // Models shouldn't contain undefined - only nulls where a value isn't present.
@@ -276,6 +277,21 @@ class ModelConversionVisitor extends Visitor<any, any[] | null, any | null> {
     if (this.objects.has(value))
       return this.objects.get(value)! as Model<TMeta>;
 
+    if ("$ref" in value) {
+      const target = this.refs.get(value.$ref);
+      if (!target) {
+        console.warn(`Unresolved $ref ${value.$ref} in object`);
+      }
+      value = target;
+    }
+
+    if ("$id" in value) {
+      this.refs.set(value.$id, value);
+      if (this.mode == "convert") {
+        delete value.$id;
+      }
+    }
+
     const props = meta.props;
 
     let target: Indexable<Model<TMeta>>;