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 操作库,使用起来也是非常方便,有时候也可能会不小心就踩坑了,这次就踩了一个,坑是这样的,如果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。。然后遍历这个对象,输出其中的值,如果是一个自定义的类型而且还有其他属性,其他属性就会被忽略,序列化之后就会发生数据丢失。

问题代码

在我的公用类库 WeihanLi.Common 有一个分页列表的Model:

在 1.0.21及之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;
    }
}

上面的这种定义相当于实现了 IEnumerable 接口,之所以实现这个接口,是因为可以直接遍历这个对象,不需要遍历这个对象的Data 属性上遍历,但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 接口就可以了,修改后的代码如下所示:

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,原来的代码类型改为 PagedListModel1 ,测试代码如下:

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]

可以看到实现了 IEnumerable 接口的那个类序列化之后一些属性丢失了

Research

查看 Newtonsoft.Json 源码 https://github.com/JamesNK/Newtonsoft.Json
,找到为什么实现了 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

ContractResolver.CreateContract

可以看到只要实现了 IEnumerable 接口,就会被当作是一个Json 数组,foreach 遍历其中的元素,其他属性就会被忽略掉了,这就是为什么上面我们实现了 IEnumerable 接口的对象序列化之后发生属性丢失的原因。

Reference

posted @ 2019-06-25 10:47 WeihanLi 阅读(...) 评论(...) 编辑 收藏