chore: cherry picked inverse relationships from hooks branch

Author: maurei

src/JsonApiDotNetCore/Data/DefaultEntityRepository.cs

@@ -281,7 +281,6 @@ private IList GetTrackedManyRelationshipValue(IEnumerable<IIdentifiable> relatio
         // helper method used in GetTrackedRelationshipValue. See comments there.
         private IIdentifiable GetTrackedHasOneRelationshipValue(IIdentifiable relationshipValue, HasOneAttribute hasOneAttribute, ref bool wasAlreadyAttached)
         {
-
             var tracked = AttachOrGetTracked(relationshipValue);
             if (tracked != null) wasAlreadyAttached = true;
             return tracked ?? relationshipValue;

src/JsonApiDotNetCore/Extensions/IApplicationBuilderExtensions.cs

@@ -4,6 +4,7 @@
 using JsonApiDotNetCore.Middleware;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 
 namespace JsonApiDotNetCore.Extensions
@@ -21,6 +22,12 @@ public static IApplicationBuilder UseJsonApi(this IApplicationBuilder app, bool
             if (useMvc)
                 app.UseMvc();
 
+            using (var scope = app.ApplicationServices.CreateScope())
+            {
+                var inverseRelationshipResolver = scope.ServiceProvider.GetService<IInverseRelationships>();
+                inverseRelationshipResolver?.Resolve();
+            }
+
             return app;
         }
 

src/JsonApiDotNetCore/Extensions/IServiceCollectionExtensions.cs

@@ -155,6 +155,9 @@ public static void AddJsonApiInternals(
             services.AddScoped<IControllerContext, Services.ControllerContext>();
             services.AddScoped<IDocumentBuilderOptionsProvider, DocumentBuilderOptionsProvider>();
 
+            services.AddScoped<IInverseRelationships, InverseRelationships>();
+
+
             // services.AddScoped<IActionFilter, TypeMatchFilter>();
         }
 

src/JsonApiDotNetCore/Internal/InverseRelationships.cs

@@ -0,0 +1,65 @@
+using System;
+using JsonApiDotNetCore.Data;
+using JsonApiDotNetCore.Models;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata;
+
+namespace JsonApiDotNetCore.Internal
+{
+    /// <summary>
+    /// Responsible for populating the RelationshipAttribute InverseNavigation property.
+    /// 
+    /// This service is instantiated in the configure phase of the application.
+    /// 
+    /// When using a data access layer different from EF Core, and when using ResourceHooks
+    /// that depend on the inverse navigation property (BeforeImplicitUpdateRelationship),
+    /// you will need to override this service, or pass along the inverseNavigationProperty in
+    /// the RelationshipAttribute.
+    /// </summary>
+    public interface IInverseRelationships
+    {
+        void Resolve();
+    }
+
+    public class InverseRelationships : IInverseRelationships
+    {
+        private readonly ResourceGraph _graph;
+        private readonly IDbContextResolver _resolver;
+
+        public InverseRelationships(IResourceGraph graph, IDbContextResolver resolver = null)
+        {
+            _graph = (ResourceGraph)graph;
+            _resolver = resolver;
+        }
+
+        public void Resolve()
+        {
+            if (EntityFrameworkCoreIsEnabled())
+            {
+                DbContext context = _resolver.GetContext();
+
+                foreach (ContextEntity ce in _graph.Entities)
+                {
+                    IEntityType meta = context.Model.FindEntityType(ce.EntityType);
+                    if (meta == null) continue;
+                    foreach (var attr in ce.Relationships)
+                    {
+                        if (attr is HasManyThroughAttribute) continue;
+                        INavigation inverseNavigation = meta.FindNavigation(attr.InternalRelationshipName)?.FindInverse();
+                        attr.InverseNavigation = inverseNavigation?.Name;
+                    }
+                }
+            }
+        }
+
+        /// <summary>
+        /// If EF Core is not being used, we're expecting the resolver to not be registered.
+        /// </summary>
+        /// <returns><c>true</c>, if entity framework core was enabled, <c>false</c> otherwise.</returns>
+        /// <param name="resolver">Resolver.</param>
+        private bool EntityFrameworkCoreIsEnabled()
+        {
+            return _resolver != null;
+        }
+    }
+}

src/JsonApiDotNetCore/Models/HasManyAttribute.cs

@@ -24,9 +24,11 @@ public class HasManyAttribute : RelationshipAttribute
         /// </code>
         /// 
         /// </example>
-        public HasManyAttribute(string publicName = null, Link documentLinks = Link.All, bool canInclude = true, string mappedBy = null)
+        public HasManyAttribute(string publicName = null, Link documentLinks = Link.All, bool canInclude = true, string mappedBy = null, string inverseNavigationProperty = null)
         : base(publicName, documentLinks, canInclude, mappedBy)
-        { }
+        {
+            InverseNavigation = inverseNavigationProperty;
+        }
 
         /// <summary>
         /// Sets the value of the property identified by this attribute

src/JsonApiDotNetCore/Models/HasOneAttribute.cs

@@ -28,11 +28,14 @@ public class HasOneAttribute : RelationshipAttribute
         /// </code>
         /// 
         /// </example>
-        public HasOneAttribute(string publicName = null, Link documentLinks = Link.All, bool canInclude = true, string withForeignKey = null, string mappedBy = null)
+        public HasOneAttribute(string publicName = null, Link documentLinks = Link.All, bool canInclude = true, string withForeignKey = null, string mappedBy = null, string inverseNavigationProperty = null)
         : base(publicName, documentLinks, canInclude, mappedBy)
         {
             _explicitIdentifiablePropertyName = withForeignKey;
+            InverseNavigation = inverseNavigationProperty;
         }
+        public string InverseNavigation { get; internal set; }
+
 
         private readonly string _explicitIdentifiablePropertyName;
 

src/JsonApiDotNetCore/Models/RelationshipAttribute.cs

@@ -15,8 +15,10 @@ protected RelationshipAttribute(string publicName, Link documentLinks, bool canI
         }
 
         public string PublicRelationshipName { get; internal set; }
-        public string InternalRelationshipName { get; internal set; } 
-        
+        public string InternalRelationshipName { get; internal set; }
+
+        public string InverseNavigation { get; internal set; }
+
         /// <summary>
         /// The related entity type. This does not necessarily match the navigation property type.
         /// In the case of a HasMany relationship, this value will be the generic argument type.