hack(service-collection-ext): inject bogus dbContext types for DI

as far as I can tell, .Net's native DI will check all pathways for resolution even if they shouldn't be resolved. Specifically, the Internal.Generics classes require DbContext to be injected. However, they would never be resolved if the app does not actually use EF and implements their own IResourceService

Author: jaredcnance

src/JsonApiDotNetCore/Builders/ContextGraphBuilder.cs

@@ -10,7 +10,7 @@ namespace JsonApiDotNetCore.Builders
     public class ContextGraphBuilder : IContextGraphBuilder
     {
         private List<ContextEntity> Entities;
-
+        private bool _usesDbContext;
         public ContextGraphBuilder()
         {
             Entities = new List<ContextEntity>();
@@ -20,7 +20,8 @@ public IContextGraph Build()
         {
             var graph = new ContextGraph()
             {
-                Entities = Entities
+                Entities = Entities,
+                UsesDbContext = _usesDbContext
             };
 
             return graph;
@@ -81,6 +82,8 @@ protected virtual Type GetRelationshipType(RelationshipAttribute relation, Prope
 
         public void AddDbContext<T>() where T : DbContext
         {
+            _usesDbContext = true;
+            
             var contextType = typeof(T);
 
             var entities = new List<ContextEntity>();

src/JsonApiDotNetCore/Extensions/IServiceCollectionExtensions.cs

@@ -55,6 +55,13 @@ public static void AddJsonApi(this IServiceCollection services,
 
             options(config);
 
+            mvcBuilder
+                .AddMvcOptions(opt =>
+                {
+                    opt.Filters.Add(typeof(JsonApiExceptionFilter));
+                    opt.SerializeAsJsonApi(config);
+                });
+
             AddJsonApiInternals(services, config);
         }
 
@@ -73,6 +80,12 @@ public static void AddJsonApiInternals(
             this IServiceCollection services,
             JsonApiOptions jsonApiOptions)
         {
+            if(!jsonApiOptions.ContextGraph.UsesDbContext)
+            {
+                services.AddScoped<DbContext>();
+                services.AddSingleton<DbContextOptions>(new DbContextOptionsBuilder().Options);
+            }
+
             services.AddScoped(typeof(IEntityRepository<>), typeof(DefaultEntityRepository<>));
             services.AddScoped(typeof(IEntityRepository<,>), typeof(DefaultEntityRepository<,>));
             services.AddScoped(typeof(IResourceService<>), typeof(EntityResourceService<>));

src/JsonApiDotNetCore/Internal/ContextGraph.cs

@@ -8,6 +8,7 @@ namespace JsonApiDotNetCore.Internal
     public class ContextGraph : IContextGraph
     {
         public List<ContextEntity> Entities { get; set; }
+        public bool UsesDbContext  { get; set; }
 
         public ContextEntity GetContextEntity(string dbSetName)
         {

src/JsonApiDotNetCore/Internal/IContextGraph.cs

@@ -8,5 +8,6 @@ public interface IContextGraph
         string GetRelationshipName<TParent>(string relationshipName);
         ContextEntity GetContextEntity(string dbSetName);
         ContextEntity GetContextEntity(Type entityType);
+        bool UsesDbContext { get; set; }
     }
 }