An exception has occurred while using the formatter ‘JsonMediaTypeFormatter’ to generate sample

HelpPage 生成 Response Sample 报异常：

An exception has occurred while using the formatter ‘JsonMediaTypeFormatter’ to generate sample for media type ‘text/json’. Exception message: One or more errors occurred.

以下尝试解决：

1、

http://www.pooran.in/?p=206

http://stackoverflow.com/questions/15029576/samples-not-working-for-web-api-help-page-when-using-an-entity-framework-complex

2、

config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;//循环引用
config.Formatters.JsonFormatter.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;

3、

去掉model 属性Attribute [JsonIgnore]