Newtonsoft.Json 序列化踩坑之 IEnumerable

Newtonsoft.Json 序列化踩坑之 IEnumerable

Intro

Newtonsoft.Json 是 .NET 下最受欢迎 JSON 操做库，使用起来也是很是方便，有时候也可能会不当心就踩坑了，此次就踩了一个，坑是这样的，若是要序列化的对象实现了 IEnumerable 接口，Newtonsoft.Json 就会认为这个对象是一个数组。。而后遍历这个对象，输出其中的值，若是是一个自定义的类型并且还有其余属性，其余属性就会被忽略，序列化以后就会发生数据丢失。

问题代码

在个人公用类库 WeihanLi.Common 有一个分页列表的Model：

在 1.0.21及以前版本是这样定义的 源码

using System;
using System.Collections;
using System.Collections.Generic;

namespace WeihanLi.Common.Models
{
    /// <summary>
    /// IPagedListModel
    /// </summary>
    /// <typeparam name="T">Type</typeparam>
    public interface IPagedListModel<out T> : IReadOnlyList<T>
    {
        /// <summary>
        /// Data
        /// </summary>
        IReadOnlyList<T> Data { get; }

        /// <summary>
        /// PageNumber
        /// </summary>
        int PageNumber { get; }

        /// <summary>
        /// PageSize
        /// </summary>
        int PageSize { get; }

        /// <summary>
        /// TotalDataCount
        /// </summary>
        int TotalCount { get; set; }
    }

    /// <inheritdoc />
    /// <summary>
    /// 分页Model
    /// </summary>
    /// <typeparam name="T">Type</typeparam>
    [Serializable]
    public class PagedListModel<T> : IPagedListModel<T>
    {
        public IReadOnlyList<T> Data { get; set; }

        private int _pageNumber = 1;

        public int PageNumber
        {
            get => _pageNumber;
            set
            {
                if (value > 0)
                {
                    _pageNumber = value;
                }
            }
        }

        private int _pageSize = 10;

        public int PageSize
        {
            get => _pageSize;
            set
            {
                if (value > 0)
                {
                    _pageSize = value;
                }
            }
        }

        private int _totalCount;

        public int TotalCount
        {
            get => _totalCount;
            set
            {
                if (value > 0)
                {
                    _totalCount = value;
                }
            }
        }

        public int PageCount => Convert.ToInt32(Math.Ceiling(_totalCount * 1.0 / _pageSize));

        public IEnumerator<T> GetEnumerator()
        {
            return Data.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return Data.GetEnumerator();
        }

        public T this[int index] => Data[index];

        public int Count => Data.Count;
    }
}

上面的这种定义至关于实现了 IEnumerable 接口，之因此实现这个接口，是由于能够直接遍历这个对象，不须要遍历这个对象的Data 属性上遍历，可是这样序列化的时候就会有问题， PageNumber/PageSize/TotalPage 之类的信息序列化时就会丢失

Solution

不要实现 IEnumerable 接口就能够了，修改后的代码以下所示：

using System;
using System.Collections.Generic;

namespace WeihanLi.Common.Models
{
    /// <summary>
    /// IPagedListModel
    /// </summary>
    /// <typeparam name="T">Type</typeparam>
    public interface IPagedListModel<out T>
    {
        /// <summary>
        /// Data
        /// </summary>
        IReadOnlyList<T> Data { get; }

        /// <summary>
        /// PageNumber
        /// </summary>
        int PageNumber { get; }

        /// <summary>
        /// PageSize
        /// </summary>
        int PageSize { get; }

        /// <summary>
        /// TotalDataCount
        /// </summary>
        int TotalCount { get; set; }
    }

    /// <inheritdoc />
    /// <summary>
    /// 分页Model
    /// </summary>
    /// <typeparam name="T">Type</typeparam>
    [Serializable]
    public class PagedListModel<T> : IPagedListModel<T>
    {
        public IReadOnlyList<T> Data { get; set; }

        private int _pageNumber = 1;

        public int PageNumber
        {
            get => _pageNumber;
            set
            {
                if (value > 0)
                {
                    _pageNumber = value;
                }
            }
        }

        private int _pageSize = 10;

        public int PageSize
        {
            get => _pageSize;
            set
            {
                if (value > 0)
                {
                    _pageSize = value;
                }
            }
        }

        private int _totalCount;

        public int TotalCount
        {
            get => _totalCount;
            set
            {
                if (value > 0)
                {
                    _totalCount = value;
                }
            }
        }

        public int PageCount => Convert.ToInt32(Math.Ceiling(_totalCount * 1.0 / _pageSize));

        public T this[int index] => Data[index];

        public int Count => Data.Count;
    }
}

Test

写个示例测试一下，原来的代码类型改成 PagedListModel1 ,测试代码以下：

PagedListModel1:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;

namespace DotNetCoreSample.Test
{
    public class PagedListModel1<T> : IEnumerable<T>
    {
        public IReadOnlyList<T> Data { get; set; }

        private int _pageNumber = 1;

        public int PageNumber
        {
            get => _pageNumber;
            set
            {
                if (value > 0)
                {
                    _pageNumber = value;
                }
            }
        }

        private int _pageSize = 10;

        public int PageSize
        {
            get => _pageSize;
            set
            {
                if (value > 0)
                {
                    _pageSize = value;
                }
            }
        }

        private int _totalCount;

        public int TotalCount
        {
            get => _totalCount;
            set
            {
                if (value > 0)
                {
                    _totalCount = value;
                }
            }
        }

        public int PageCount => Convert.ToInt32(Math.Ceiling(_totalCount * 1.0 / _pageSize));

        public T this[int index] => Data[index];

        public int Count => Data.Count;

        public IEnumerator<T> GetEnumerator()
        {
            return Data.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return Data.GetEnumerator();
        }
    }
}

测试代码：

var pagedListModel = new PagedListModel<int>()
            {
                PageNumber = 2, PageSize = 2, TotalCount = 6, Data = new int[] {1, 2},
            };
var pagedListModel1 = new PagedListModel1<int>()
            {
                PageNumber = 2,
                PageSize = 2,
                TotalCount = 6,
                Data = new int[] { 1, 2 },
            };
Console.WriteLine($"pagedListModel:{JsonConvert.SerializeObject(pagedListModel)}, pagedListModel1:{JsonConvert.SerializeObject(pagedListModel1)}");

output:

pagedListModel:{"Data":[1,2],"PageNumber":2,"PageSize":2,"TotalCount":6,"PageCount":3,"Count":2}, pagedListModel1:[1,2]

能够看到实现了 IEnumerable 接口的那个类序列化以后一些属性丢失了

Research

查看 Newtonsoft.Json 源码 https://github.com/JamesNK/Newtonsoft.Json
，找到为何实现了 IEnumerable 接口就会有问题，最后找到了这里 https://github.com/JamesNK/Newtonsoft.Json/blob/master/Src/Newtonsoft.Json/Serialization/DefaultContractResolver.cs#L1218

能够看到只要实现了 IEnumerable 接口，就会被看成是一个Json 数组，foreach 遍历其中的元素，其余属性就会被忽略掉了，这就是为何上面咱们实现了 IEnumerable 接口的对象序列化以后发生属性丢失的缘由。

Reference

• https://github.com/JamesNK/Newtonsoft.Json
• https://github.com/JamesNK/Newtonsoft.Json/blob/master/Src/Newtonsoft.Json/Serialization/DefaultContractResolver.cs#L1218
• https://github.com/WeihanLi/WeihanLi.Common/blob/dev/samples/DotNetCoreSample/Program.cs