JSON反序列化失败：含categoryID=117节点时代码报错求助

错误原因分析 #

• Children类型不兼容：JSON中大部分父节点的children是键值对形式的对象（如{"57": {...}}），但categoryID=117的children是空数组[]，而原代码中Category类将Children定义为JObject，数组无法直接反序列化为JObject，这是导致执行失败的直接原因。
• 数据类型不匹配：Category类中CategoryID、ParentCategoryID等字段定义为string，但JSON中对应值是数字或null，虽Json.NET有隐式转换，但容易引发类型异常。
• 类结构冗余：ChildCategory和Category结构高度重复，没必要单独定义，用递归结构更合理。

修复步骤 #

1. 统一处理Children的类型差异 #

自定义JsonConverter，识别children字段的类型（数组或对象），将空数组转换为空字典，保证类型兼容。

2. 修正数据类型匹配 #

将Category类中数字类型字段改为int或int?（支持null），匹配JSON中的数据类型。

3. 简化类结构 #

删除ChildCategory类，用Dictionary<string, Category>存储子节点，通过递归结构处理嵌套层级。

完整修复代码 #

using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
using System.Collections.Generic;

public class Category
{
    [JsonProperty("categoryID")]
    public int CategoryID { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("description")]
    public string Description { get; set; }

    [JsonProperty("parentCategoryID")]
    public int? ParentCategoryID { get; set; }

    [JsonProperty("countDiscussions")]
    public int CountDiscussions { get; set; }

    [JsonProperty("countComments")]
    public int CountComments { get; set; }

    [JsonProperty("children")]
    [JsonConverter(typeof(ChildrenConverter))]
    public Dictionary<string, Category> Children { get; set; } = new Dictionary<string, Category>();
}

public class ChildrenConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Dictionary<string, Category>);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var token = JToken.Load(reader);
        if (token.Type == JTokenType.Array)
        {
            // 空数组转换为空字典
            return new Dictionary<string, Category>();
        }
        else if (token.Type == JTokenType.Object)
        {
            // 对象直接反序列化为字典
            return token.ToObject<Dictionary<string, Category>>(serializer);
        }
        return null;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        serializer.Serialize(writer, value);
    }
}

public class Program
{
    public static void Main()
    {
        string jsonData = @"[
        {   
            ""categoryID"": 93,
            ""name"": ""Cloths"",
            ""description"": """",
            ""parentCategoryID"": null,
            ""countDiscussions"": 10,
            ""countComments"": 20,
            ""children"": {
                ""57"": {
                    ""categoryID"": 180,
                    ""name"": ""Shirt"",
                    ""description"": """",
                    ""parentCategoryID"": 9,
                    ""countDiscussions"": 2,
                    ""countComments"": 4,
                    ""children"": []
                },
                ""56"": {
                    ""categoryID"": 187,
                    ""name"": ""ShirtAAAAA"",
                    ""description"": """",
                    ""parentCategoryID"": 9,
                    ""countDiscussions"": 2,
                    ""countComments"": 4,
                    ""children"": []
                }
            }
        },
        {
            ""categoryID"": 172,
            ""name"": ""accessories"",
            ""description"": """",
            ""parentCategoryID"": null,
            ""countDiscussions"": 15,
            ""countComments"": 47,
            ""children"": {
                ""2"": {
                    ""categoryID"": 191,
                    ""name"": ""Watch"",
                    ""description"": """",
                    ""parentCategoryID"": 172,
                    ""countDiscussions"": 1,
                    ""countComments"": 0,
                    ""children"": []
                }
            }
        },
        {
            ""categoryID"": 117,
            ""name"": ""jewellery"",
            ""description"": """",
            ""parentCategoryID"": null,
            ""countDiscussions"": 243,
            ""countComments"": 6716,
            ""children"": []
        }
    ]";

        var categories = JsonConvert.DeserializeObject<Category[]>(jsonData);

        foreach (var category in categories)
        {
            Console.WriteLine($"Category ID: {category.CategoryID}");
            Console.WriteLine($"Name: {category.Name}");
            Console.WriteLine($"Description: {category.Description}");
            Console.WriteLine($"Parent Category ID: {category.ParentCategoryID ?? 0}");
            Console.WriteLine($"Count of Discussions: {category.CountDiscussions}");
            Console.WriteLine($"Count of Comments: {category.CountComments}");
            Console.WriteLine("Children:");
            foreach (var childEntry in category.Children)
            {
                var child = childEntry.Value;
                Console.WriteLine($"    Key: {childEntry.Key}");
                Console.WriteLine($"    Category ID: {child.CategoryID}");
                Console.WriteLine($"    Name: {child.Name}");
                Console.WriteLine($"    Description: {child.Description}");
                Console.WriteLine($"    Parent Category ID: {child.ParentCategoryID ?? 0}");
                Console.WriteLine($"    Count of Discussions: {child.CountDiscussions}");
                Console.WriteLine($"    Count of Comments: {child.CountComments}");
            }
            Console.WriteLine("------------------------");
        }
    }
}

修复说明 #

1. 自定义转换器：ChildrenConverter自动处理children字段的类型差异，空数组转为空字典，避免转换异常。
2. 类型匹配：将数字类字段改为int/int?，完美适配JSON中的数字和null值，消除类型转换风险。
3. 递归结构：用Dictionary<string, Category>存储子节点，既符合JSON的键值对结构，又支持无限层级的嵌套子节点解析。
4. null值处理：输出时用?? 0将null替换为0，也可根据需求改为显示"null"。

内容的提问来源于stack exchange，提问作者Sreepu