如何防止Newtonsoft.JSON在反序列化期间设置值时重用默认值

Question

这是一种奇怪的情况，但当我们不想将数据分解成一个单独的表时，我们经常使用这种模式来处理SQL后端。

这里的问题是，在反序列化时，MyList中有两个项，而不是一个。问题的根源在于，当反序列化程序获取MyList属性时，它会重用现有值，而不是重置该属性。

这是代码：

public class Jason
{
    public object FromJSON(string json, Type t)
    {
        JsonSerializerSettings s = new JsonSerializerSettings();
        s.Converters.Add(new Newtonsoft.Json.Converters.StringEnumConverter());
        s.NullValueHandling = NullValueHandling.Ignore;
        return Newtonsoft.Json.JsonConvert.DeserializeObject(json, t, s);
    }
    public string ToJSON(object o)
    {
        JsonSerializerSettings s = new JsonSerializerSettings();
        s.Converters.Add(new Newtonsoft.Json.Converters.StringEnumConverter());
        s.NullValueHandling = NullValueHandling.Ignore;
        return Newtonsoft.Json.JsonConvert.SerializeObject(o, s);
    }
    public string MyListString
    {
        get { return ToJSON(_MyList); }
        set { _MyList = (List<string>)FromJSON(value, typeof(List<string>)); }
    }
    private List<string> _MyList = new List<string>();
    public List<string> MyList
    {
        get { return _MyList; }
        set { _MyList = value; }
    }
}
[TestFixture]
public class JasonTests : TestFixtureBase
{
    [Test]
    public void Jason()
    {
        Jason j = new Jason();
        j.MyList.Add("hello");
        string json = j.ToJSON(j);
        Jason j2 = (Jason)j.FromJSON(json, typeof(Jason));
        Assert.AreEqual(j.MyList.Count, j2.MyList.Count);
    }
}

Answer 1

好吧，在检查了源代码并试图修复我认为的错误后，在谷歌上搜索是否有其他人有这个问题，我突然想到可能有一个设置，果然有。这是固定代码：

public class Jason
{
    public object FromJSON(string json, Type t)
    {
        JsonSerializerSettings s = new JsonSerializerSettings();
        s.Converters.Add(new Newtonsoft.Json.Converters.StringEnumConverter());
        s.NullValueHandling = NullValueHandling.Ignore;
        s.ObjectCreationHandling = ObjectCreationHandling.Replace; // without this, you end up with duplicates.
        return Newtonsoft.Json.JsonConvert.DeserializeObject(json, t, s);
    }
    public string ToJSON(object o)
    {
        JsonSerializerSettings s = new JsonSerializerSettings();
        s.Converters.Add(new Newtonsoft.Json.Converters.StringEnumConverter());
        s.NullValueHandling = NullValueHandling.Ignore;
        s.ObjectCreationHandling = ObjectCreationHandling.Replace; // without this, you end up with duplicates.
        return Newtonsoft.Json.JsonConvert.SerializeObject(o, s);
    }
    public string MyListString
    {
        get { return ToJSON(_MyList); }
        set { _MyList = (List<string>)FromJSON(value, typeof(List<string>)); }
    }
    private List<string> _MyList = new List<string>();
    public List<string> MyList
    {
        get { return _MyList; }
        set { _MyList = value; }
    }
}
[TestFixture]
public class JasonTests : TestFixtureBase
{
    [Test]
    public void Jason()
    {
        Jason j = new Jason();
        j.MyList.Add("hello");
        string json = j.ToJSON(j);
        Jason j2 = (Jason)j.FromJSON(json, typeof(Jason));
        Assert.AreEqual(j.MyList.Count, j2.MyList.Count);
    }
 }