The ‘ObjectContent`1’ type Failed to serialize the response body for
content type ‘application/json; charset=utf-8’

InnerException是这样的(我在这种情况下返回JSON,与XML相同)：

"InnerException": {
"Message": "An error has occurred.","ExceptionMessage": "Error getting value from 'IdentityEqualityComparer' on 'NHibernate.Proxy.DefaultLazyInitializer'.","ExceptionType": "Newtonsoft.Json.JsonSerializationException","StackTrace": " at Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer,Object value,JsonObjectContract contract,JsonProperty member,JsonContainerContract collectionContract,JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer,JsonContract valueContract,JsonContainerContract containerContract,JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeISerializable(JsonWriter writer,ISerializable value,JsonISerializableContract contract,JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer,JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer,IWrappedCollection values,JsonArrayContract contract,JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter,Object value) at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter,Object value) at System.Net.Http.Formatting.JsonMediaTypeFormatter.<>c__DisplayClassd.<WriteToStreamAsync>b__c() at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action,CancellationToken token)","InnerException": {
"Message": "An error has occurred.","ExceptionMessage": "Common Language Runtime detected an invalid program.","ExceptionType": "System.InvalidProgramException","StackTrace": " at GetIdentityEqualityComparer(Object ) at Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)"
}

这是我运行的代码：

// GET api/benchmark/getincomplete
        [HttpGet]
        public IList<Benchmark> GetIncomplete()
        {
            var s = HibernateModule.CurrentSession;
            var benchList = s.QueryOver<Benchmark>()
                                .Where(b => !b.Completed)
                                .Where(b => !b.Deleted)
                                .OrderBy(b => b.Id).Asc
                                .List<Benchmark>();
 
            return benchList;
        }

这是基准模型：

public class Benchmark
    {
        public virtual int Id { get; set; }
        [required]
        [DataType(DataType.Date)]
        public virtual DateTime Date { get; set; }
        [required,ScriptIgnore]
        public virtual IList<TestResult> Results { get; set; }
        [required]
        public virtual IList<TestCase> TestCases { get; set; }
        [AllowHtml]
        public virtual string Description { get; set; }
        public virtual Device Device { get; set; }        
        public virtual bool Published { get; set; }
        [Display(Name = "Deleted"),ScriptIgnore]
        public virtual bool Deleted { get; set; }
        public virtual bool Completed { get; set; }
 
        public Benchmark() 
        {
            Results = new List<TestResult>();
            TestCases = new List<TestCase>();
            Published = false;
            Deleted = false;
            Completed = false;
        }
    }

我不太清楚问题所在.可能是NHibernate Proxy(我使用Fluent NHibernate)吗？奇怪的是,如果我不使用ApiController,并手动返回JSON,这很好用！

更新：

根据下面的答案,这是我在Application_Start()中添加的代码：

HttpConfiguration config = GlobalConfiguration.Configuration;
((DefaultContractResolver)config.Formatters.JsonFormatter.SerializerSettings.ContractResolver).IgnoreSerializableAttribute = true;