OData WebAPI 2 - 属性方法返回 xml 而不是 json

Question

我正在使用 OData WebAPI 2。 所有操作（获取实体集、通过 id 获取实体...）都返回 json 当我尝试获取导航属性时，它会返回预期的 json 响应。 但是当我试图获取一个属性时，响应是 xml，这不是预期的。

这是我的控制器代码：

    /// <summary>
    /// Gets the navigation property.
    /// </summary>
    /// <param name="key">The key.</param>
    /// <returns></returns>
    public virtual HttpResponseMessage GetNavigationProperty([FromODataUri] string key) {
        ODataPath oDataPath = this.Request.GetODataPath();
        var navigationPropertyName = (oDataPath.Segments[2] as NavigationPathSegment).NavigationPropertyName;
        return GetProperty(key, navigationPropertyName);
    }

    /// <summary>
    /// Gets the property.
    /// </summary>
    /// <returns></returns>
    public virtual HttpResponseMessage GetProperty() {
        ODataPath oDataPath = this.Request.GetODataPath();
        var propertyName = (oDataPath.Segments[2] as PropertyAccessPathSegment).PropertyName;
        var key = (oDataPath.Segments[1] as KeyValuePathSegment).Value;
        return GetProperty(key, propertyName);
    }

    private HttpResponseMessage GetProperty(string key, string propertyName) {
        var entity = GetEntities(key, new[] { propertyName }).FirstOrDefault();
        var content = typeof(TEntity).GetProperty(propertyName).GetValue(entity, null);

        // There are two System.Net.Http.HttpRequestMessageExtensions classes in two different dlls, we want the one on System.Web.Http.dll
        var assembly = AppDomain.CurrentDomain.GetAssemblies().First(x => x.FullName.StartsWith("System.Web.Http,"));
        var type = assembly.GetType("System.Net.Http.HttpRequestMessageExtensions");
        // Method with parameter T, can't get it via GetMethod so we look it up as the only CreateResponse with 3 parameters.
        MethodInfo method = type.GetMethods().First(x => x.Name == "CreateResponse" && x.GetParameters().Length == 3);
        MethodInfo generic = method.MakeGenericMethod(content.GetType());
        var response = generic.Invoke(Request, new[] { Request, HttpStatusCode.OK, content });

        // Return our response.
        return response as HttpResponseMessage;
    }

我做错了什么吗？ 谢谢！ 暗里。

Answer 1

这是意料之中的，因为大多数浏览器的接受标头中都有 application/xml。比如chrome发送这个

text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8

OData 协议将实体和实体集合指定为application/atom+xml，将属性（复杂、原始、复杂集合、原始集合）指定为application/xml。以上所有内容都可以并且将在世界的 json 端格式化为 application/json。

当您从浏览器请求实体或提要时，上述接受标头中没有可以根据 OData 规范格式化实体/提要的内容类型。所以，我们默认为application/json。但是，如果您要求一个属性（非导航），则接受标头中有一个匹配 application/xml。所以，我们发回application/xml。