如何使用Json.Net将JSON数组反序列化为对象? [英] How to deserialize a JSON array into an object using Json.Net?

问题描述

我有一个带有JSON数组的有效JSON对象. JSON数组没有花括号，并且包含逗号分隔的混合类型列表.看起来像这样:

I've a valid JSON object that has a JSON array in it. The JSON array doesn't have curly braces and contains a comma separated list of mixed type in it. It looks like this:

{
    "ID": 17,
    "Days": 979,
    "Start_Date": "10/13/2012",
    "End_Date": "11/12/2012",
    "State": "",
    "Page": 1,
    "Test": "Valid",
    "ROWS": [
        [441210, "A", "12/31/2009", "OK", "Done", "KELLEY and Co'", "12/31/2009", "06/29/2010", "TEXAS", "Lawyers", 6, "", "<img src=\"/includes/images/Icon_done.gif\" border=\"0\" alt=\"Done\" title=\"Done\" />"],
        [441151, "B", "12/31/2009", "No", "In-process", "Sage & Co", "12/31/2009", "06/29/2010", "CALIFORNIA", "Realtor", 6, "", "<img src=\"/includes/images/Icon_InProcess.gif\" border=\"0\" alt=\"In Process\" title=\"In Process\" />"]
    ]
}

我创建了一个反映JSON结构的类，并为复杂数组提供了一个列表:

I've created a class to reflect the JSON structure, having a List for the complex array:

class myModel
{
    public int ID { get; set; }
    public int Days { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
    public string State { get; set; }
    public string Page { get; set; }
    public string Test { get; set; }
    List<ChildModel> Rows { get; set; }
}

我也已经使用列表列表进行了测试:

I've tested it with a List of a List too:

List<List<ChildModel>> Rows { get; set; }

子模型如下:

class ChildModel
{
    public int ID { get; set; }
    public string StatusId { get; set; }
    public DateTime ContactDate { get; set; }
    public string State { get; set; }
    public string Status { get; set; }
    public string CustomerName { get; set; }
    public DateTime WorkStartDate { get; set; }
    public DateTime WorkEndDate { get; set; }
    public string Territory { get; set; }
    public string CustType { get; set; }
    public int JobOrder { get; set; }
    public string Filler { get; set; }
    public string Link { get; set; }
}

在我的program.cs文件中，我这样反序列化:

In my program.cs file, I'm deserializing it like this:

using (StreamReader r = new StreamReader(@"D:\01.json"))
{
    myModel items = JsonConvert.DeserializeObject<myModel>(r.ReadToEnd());
}

运行此程序时，子对象(行)始终为null.我在做什么错了?

When I run this program, the child object (Rows) is always null. What am I doing wrong?

推荐答案

Json.Net不具有将数组自动映射到类的功能.为此，您需要自定义JsonConverter.这是一个应该为您工作的通用转换器.它使用自定义的[JsonArrayIndex]属性来标识类中的哪些属性与数组中的哪些索引相对应.如果JSON更改，这将使您可以轻松地更新模型.另外，您可以安全地忽略类中不需要的属性，例如Filler.

Json.Net does not have a facility to automatically map an array into a class. To do so you need a custom JsonConverter. Here is a generic converter that should work for you. It uses a custom [JsonArrayIndex] attribute to identify which properties in the class correspond to which indexes in the array. This will allow you to easily update your model if the JSON changes. Also, you can safely omit properties from your class that you don't need, such as Filler.

这是代码:

public class JsonArrayIndexAttribute : Attribute
{
    public int Index { get; private set; }
    public JsonArrayIndexAttribute(int index)
    {
        Index = index;
    }
}

public class ArrayToObjectConverter<T> : JsonConverter where T : class, new()
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(T);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JArray array = JArray.Load(reader);

        var propsByIndex = typeof(T).GetProperties()
            .Where(p => p.CanRead && p.CanWrite && p.GetCustomAttribute<JsonArrayIndexAttribute>() != null)
            .ToDictionary(p => p.GetCustomAttribute<JsonArrayIndexAttribute>().Index);

        JObject obj = new JObject(array
            .Select((jt, i) =>
            {
                PropertyInfo prop;
                return propsByIndex.TryGetValue(i, out prop) ? new JProperty(prop.Name, jt) : null;
            })
            .Where(jp => jp != null)
        );

        T target = new T();
        serializer.Populate(obj.CreateReader(), target);

        return target;
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

要使用转换器，您需要标记ChildModel类，如下所示:

To use the converter, you need to mark up your ChildModel class as shown below:

[JsonConverter(typeof(ArrayToObjectConverter<ChildModel>))]
class ChildModel
{
    [JsonArrayIndex(0)]
    public int ID { get; set; }
    [JsonArrayIndex(1)]
    public string StatusId { get; set; }
    [JsonArrayIndex(2)]
    public DateTime ContactDate { get; set; }
    [JsonArrayIndex(3)]
    public string State { get; set; }
    [JsonArrayIndex(4)]
    public string Status { get; set; }
    [JsonArrayIndex(5)]
    public string CustomerName { get; set; }
    [JsonArrayIndex(6)]
    public DateTime WorkStartDate { get; set; }
    [JsonArrayIndex(7)]
    public DateTime WorkEndDate { get; set; }
    [JsonArrayIndex(8)]
    public string Territory { get; set; }
    [JsonArrayIndex(9)]
    public string CustType { get; set; }
    [JsonArrayIndex(10)]
    public int JobOrder { get; set; }
    [JsonArrayIndex(12)]
    public string Link { get; set; }
}

然后像往常一样反序列化，它应该可以按需要工作.这是一个演示: https://dotnetfiddle.net/n3oE3L

Then just deserialize as usual and it should work as you wanted. Here is a demo: https://dotnetfiddle.net/n3oE3L

注意:我没有实现WriteJson，因此，如果您将模型序列化回JSON，它将不会序列化回数组格式.而是使用默认的对象序列化.

Note: I did not implement WriteJson, so if you serialize your model back to JSON, it will not serialize back to the array format; instead it will use the default object serialization.

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