Fixed: Casing convention in error response for invalid modal state

src/JsonApiDotNetCore/Builders/ResourceGraphBuilder.cs

@@ -227,8 +227,7 @@ private string FormatResourceName(Type resourceType)
 
         private string FormatPropertyName(PropertyInfo resourceProperty)
         {
-            var contractResolver = (DefaultContractResolver)_options.SerializerSettings.ContractResolver;
-            return contractResolver.NamingStrategy.GetPropertyName(resourceProperty.Name, false);
+            return _options.SerializerContractResolver.NamingStrategy.GetPropertyName(resourceProperty.Name, false);
         }
     }
 }

src/JsonApiDotNetCore/Configuration/IJsonApiOptions.cs

@@ -1,6 +1,7 @@
 using System;
 using JsonApiDotNetCore.Models.JsonApiDocuments;
 using Newtonsoft.Json;
+using Newtonsoft.Json.Serialization;
 
 namespace JsonApiDotNetCore.Configuration
 {
@@ -59,5 +60,7 @@ public interface IJsonApiOptions : ILinksConfiguration
         /// </example>
         /// </summary>
         JsonSerializerSettings SerializerSettings { get; }
+
+        internal DefaultContractResolver SerializerContractResolver => (DefaultContractResolver)SerializerSettings.ContractResolver;
     }
 }

src/JsonApiDotNetCore/Controllers/BaseJsonApiController.cs

@@ -6,6 +6,7 @@
 using JsonApiDotNetCore.Services;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Logging;
+using Newtonsoft.Json.Serialization;
 
 namespace JsonApiDotNetCore.Controllers
 {
@@ -114,7 +115,10 @@ public virtual async Task<IActionResult> PostAsync([FromBody] T entity)
                 throw new ResourceIdInPostRequestNotAllowedException();
 
             if (_jsonApiOptions.ValidateModelState && !ModelState.IsValid)
-                throw new InvalidModelStateException(ModelState, typeof(T), _jsonApiOptions.IncludeExceptionStackTraceInErrors);
+            {
+                var namingStrategy = _jsonApiOptions.SerializerContractResolver.NamingStrategy;
+                throw new InvalidModelStateException(ModelState, typeof(T), _jsonApiOptions.IncludeExceptionStackTraceInErrors, namingStrategy);
+            }
 
             entity = await _create.CreateAsync(entity);
 
@@ -130,7 +134,10 @@ public virtual async Task<IActionResult> PatchAsync(TId id, [FromBody] T entity)
                 throw new InvalidRequestBodyException(null, null, null);
 
             if (_jsonApiOptions.ValidateModelState && !ModelState.IsValid)
-                throw new InvalidModelStateException(ModelState, typeof(T), _jsonApiOptions.IncludeExceptionStackTraceInErrors);
+            {
+                var namingStrategy = _jsonApiOptions.SerializerContractResolver.NamingStrategy;
+                throw new InvalidModelStateException(ModelState, typeof(T), _jsonApiOptions.IncludeExceptionStackTraceInErrors, namingStrategy);
+            }
 
             var updatedEntity = await _update.UpdateAsync(id, entity);
             return updatedEntity == null ? Ok(null) : Ok(updatedEntity);

src/JsonApiDotNetCore/Exceptions/InvalidModelStateException.cs

@@ -6,6 +6,7 @@
 using JsonApiDotNetCore.Models;
 using JsonApiDotNetCore.Models.JsonApiDocuments;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Newtonsoft.Json.Serialization;
 
 namespace JsonApiDotNetCore.Exceptions
 {
@@ -17,13 +18,13 @@ public class InvalidModelStateException : Exception
         public IList<Error> Errors { get; }
 
         public InvalidModelStateException(ModelStateDictionary modelState, Type resourceType,
-            bool includeExceptionStackTraceInErrors)
+            bool includeExceptionStackTraceInErrors, NamingStrategy namingStrategy)
         {
-            Errors = FromModelState(modelState, resourceType, includeExceptionStackTraceInErrors);
+            Errors = FromModelState(modelState, resourceType, includeExceptionStackTraceInErrors, namingStrategy);
         }
 
         private static List<Error> FromModelState(ModelStateDictionary modelState, Type resourceType,
-            bool includeExceptionStackTraceInErrors)
+            bool includeExceptionStackTraceInErrors, NamingStrategy namingStrategy)
         {
             List<Error> errors = new List<Error>();
 
@@ -32,9 +33,8 @@ private static List<Error> FromModelState(ModelStateDictionary modelState, Type
                 var propertyName = pair.Key;
                 PropertyInfo property = resourceType.GetProperty(propertyName);
 
-                // TODO: Need access to ResourceContext here, in order to determine attribute name when not explicitly set.
                 string attributeName =
-                    property?.GetCustomAttribute<AttrAttribute>().PublicAttributeName ?? property?.Name;
+                    property.GetCustomAttribute<AttrAttribute>().PublicAttributeName ?? namingStrategy.GetPropertyName(property.Name, false);
 
                 foreach (var modelError in pair.Value.Errors)
                 {

src/JsonApiDotNetCore/Graph/ResourceNameFormatter.cs

@@ -13,8 +13,7 @@ internal sealed class ResourceNameFormatter
 
         public ResourceNameFormatter(IJsonApiOptions options)
         {
-            var contractResolver = (DefaultContractResolver) options.SerializerSettings.ContractResolver;
-            _namingStrategy = contractResolver.NamingStrategy;
+            _namingStrategy = options.SerializerContractResolver.NamingStrategy;
         }
 
         /// <summary>

src/JsonApiDotNetCore/Internal/DefaultRoutingConvention.cs

@@ -107,8 +107,7 @@ private string TemplateFromResource(ControllerModel model)
         /// </summary>
         private string TemplateFromController(ControllerModel model)
         {
-            var contractResolver = (DefaultContractResolver) _options.SerializerSettings.ContractResolver;
-            string controllerName = contractResolver.NamingStrategy.GetPropertyName(model.ControllerName, false);
+            string controllerName = _options.SerializerContractResolver.NamingStrategy.GetPropertyName(model.ControllerName, false);
 
             var template = $"{_options.Namespace}/{controllerName}";
             if (_registeredTemplates.Add(template))

test/JsonApiDotNetCoreExampleTests/Acceptance/ModelStateValidationTests.cs

@@ -53,7 +53,7 @@ public async Task When_posting_tag_with_invalid_name_it_must_fail()
             Assert.Equal(HttpStatusCode.UnprocessableEntity, errorDocument.Errors[0].StatusCode);
             Assert.Equal("Input validation failed.", errorDocument.Errors[0].Title);
             Assert.Equal("The field Name must match the regular expression '^\\W$'.", errorDocument.Errors[0].Detail);
-            Assert.Equal("/data/attributes/Name", errorDocument.Errors[0].Source.Pointer);
+            Assert.Equal("/data/attributes/name", errorDocument.Errors[0].Source.Pointer);
         }
 
         [Fact]
@@ -127,7 +127,7 @@ public async Task When_patching_tag_with_invalid_name_it_must_fail()
             Assert.Equal(HttpStatusCode.UnprocessableEntity, errorDocument.Errors[0].StatusCode);
             Assert.Equal("Input validation failed.", errorDocument.Errors[0].Title);
             Assert.Equal("The field Name must match the regular expression '^\\W$'.", errorDocument.Errors[0].Detail);
-            Assert.Equal("/data/attributes/Name", errorDocument.Errors[0].Source.Pointer);
+            Assert.Equal("/data/attributes/name", errorDocument.Errors[0].Source.Pointer);
         }
 
         [Fact]