Net在创建我的自定义JsonConverter时出错

Question

我有一个问题，我希望生成一个JSON字段，其中字段名称在运行时是已知的，例如：

{ "known_at_run_time": ["test","test","test"] }

所以我试着用这种方式实现它，但每当我运行单元测试时，我都会收到一个错误，说我的自定义JsonConverter无法创建。这是我的代码：

TermFilter.cs

public enum ExecutionType { plain, fielddata, @bool, and, or }
[JsonObject(MemberSerialization.OptIn)]
public class TermFilter
{
#region PROPERTIES
private JsonTuple query;
private ExecutionType execution;
private string _execution;
private bool _cache;
#endregion
#region CONSTRUCTOR
public TermFilter()
{
try
{
this.query = null;
this.Execution = ExecutionType.plain;
this.Cache = true;
}
catch(Exception)
{
throw;
}
}
public TermFilter(ExecutionType execution)
: this()
{
try
{
this.Execution = execution;
}
catch (Exception)
{
throw;
}
}
public TermFilter(ExecutionType execution, bool cache)
: this(execution)
{
try
{
this.Cache = cache;
}
catch (Exception)
{
throw;
}
}
public TermFilter(string field, string[] terms)
:this()
{
try
{
this.Query = new JsonTuple(field, new HashSet<string>(terms));
}
catch (Exception)
{
throw;
}
}
#endregion
#region GET/SET
//[JsonProperty(ItemConverterType = typeof(JsonTupleConverter))]
//[JsonProperty]
[JsonConverter( typeof(JsonTupleConverter) )]
public JsonTuple Query
{
get { return query; }
set { query = value; }
}
public ExecutionType Execution
{
get { return execution; }
set 
{ 
execution = value;
_execution = value.ToString();
}
}
[JsonProperty(PropertyName = "execution")]
public string _Execution
{
get { return _execution; }
set { _execution = value; }
}
[JsonProperty(PropertyName = "_cache")]
public bool Cache
{
get { return _cache; }
set { _cache = value; }
}
#endregion
#region METHODS
public TermFilter AddTerm(string term)
{
try
{
if (!this.query.Data.Contains(term))
this.query.Data.Add(term);
return this;
}
catch (Exception)
{
throw;
}
}
public string ToJson()
{
try
{
var settings = new JsonSerializerSettings();
settings.TypeNameHandling = TypeNameHandling.Objects;
settings.Converters.Add(new JsonTupleConverter(new Type[] { typeof(JsonTuple) }));
settings.NullValueHandling = NullValueHandling.Ignore;
return JsonConvert.SerializeObject(this, settings);
//return JsonConvert.SerializeObject(this, Formatting.None, new JsonTupleConverter(typeof(JsonTuple)));
//return JsonConvert.SerializeObject(this, Formatting.None, new JsonConverter[] { new JsonTupleConverter(typeof(JsonTuple)),  });
}
catch (Exception)
{
throw;
}
}
#endregion
}

JsonTuple.cs

public class JsonTuple
{
#region PROPERTIES
private string field;
private HashSet<string> data;
#endregion
#region CONSTRUCTOR
public JsonTuple()
{
try
{
this.field = null;
this.data = null;
}
catch (Exception)
{
throw;
}
}
public JsonTuple(string field, HashSet<string> data)
{
try
{
this.field = field;
this.data = data;
}
catch (Exception)
{
throw;
}
}
#endregion
#region GET/SET
public string Field
{
get { return field; }
set { field = value; }
}
public HashSet<string> Data
{
get { return data; }
set { data = value; }
}
#endregion
#region METHODS
public string ToJson()
{
try
{
return JsonConvert.SerializeObject(this, Formatting.None, new JsonTupleConverter(typeof(JsonTuple)));
}
catch (Exception)
{
throw;
}
}
#endregion
}

JsonTupleConverter.cs

public class JsonTupleConverter : JsonConverter
{
private readonly Type[] _types;
public JsonTupleConverter(params Type[] types)
{
try
{
_types = types;
}
catch (Exception)
{
throw;
}
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
try
{
JToken t = JToken.FromObject(value);
if (t.Type != JTokenType.Object)
{
t.WriteTo(writer);
}
else if (!_types.Any(_t => _t == value.GetType()))
{
serializer.Serialize(writer, value);
}
else
{
JsonTuple tuple = (JsonTuple)value;
if ((tuple != null) && (tuple.Field != null) && (tuple.Data != null))
{
JToken entityToken = null;
if (tuple.Data != null)
entityToken = JToken.FromObject(tuple.Data);
JObject o = new JObject();
o.AddFirst(new JProperty(tuple.Field, entityToken));
o.WriteTo(writer);
}
}
}
catch (Exception)
{
throw;
}
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException("Unnecessary because CanRead is false. The type will skip the converter.");
}
public override bool CanRead
{
get { return false; }
}
public override bool CanConvert(Type objectType)
{
return _types.Any(t => t == objectType);
}
}

测试.cs

[TestMethod]
public void TermFieldSertialization()
{
try
{
TermFilter filter = new TermFilter("test.field", new string[] {"test1", "test2", "test3"});
Assert.IsNotNull(filter);
string sampleJson = filter.ToJson();
Assert.IsNotNull(sampleJson);
}
catch (Exception)
{
throw;
}
}

我做错了什么？任何信息都会有所帮助。

Answer 1

首先，尝试从TermFilter类的Query属性中删除[JsonConverter]属性。您不需要它，因为Query属性是JsonTuple，并且您已经将JsonTupleConverter的实例传递给ToJson()方法中的JsonConvert.SerializeObject()方法，指定它可以处理JsonTuples。这将消除错误。

然而，还有另一个问题。您的意图似乎是让Query属性序列化为JSON，但就目前情况来看，这不会发生。这是因为您已经用[JsonObject(MemberSerialization.OptIn)]标记了TermFilter类，而Query属性缺少[JsonProperty]属性来表示您希望该属性包含在输出中。您需要添加[JsonProperty("query")]来修复此问题。一旦你做到了，你应该得到你期望的输出。

顺便说一句，如果你只想再次抛出异常，而不想对它们做任何其他事情，那么你就不需要捕捉异常。我在您的代码中随处可见这种模式。相反，完全忽略try/catch；它做了完全相同的事情，并将使您的代码更加简洁。只有当你打算处理一个异常时才能捕获它。

Answer 2

我认为发生异常是因为JsonTupleConverter没有无参数构造函数。

public JsonTupleConverter() { }

如果添加了这一点，错误应该会消失，但您的代码可能无法工作，因为它可能试图在没有正确设置类型的情况下使用转换器。

也许你应该把它序列化为一本字典？例如

var myDict = new Dictionary<string, List<string>>
{
{ "known_at_run_time", new List<string> { "test","test","test" } }
};
string ser = JsonConvert.SerializeObject(myDict);
// ser is {"known_at_run_time":["test","test","test"]}