如何序列化继承的 ICollection 中的属性<t> class？</t>

Question

I have a class that presented like

public class ItemCollection<T> : ICollection<T> {
    public ItemCollection() {
        Items = new List<T>();
    }
    public List<T> Items { get; set; }
    ...
}

Now it will be serialized into:

{
    "Property": [{...}]
}

But I want the result is like:

{
    "Property": {"Items": [{...}]}
}

Sorry for the missing information of this question.

I now stuck in serialization when using System.Text.Json.

In Newtonsoft.Json, I use [JsonObject] to annotate this class so it can serialization correctly into json with "Items": value , but I don't know how to serialize the Items property using System.Text.Json.

I have some classes inherited this class and the inheritances will be as properties in other classes.

Solution:

Thank you for every one that answered this question, I have found a solution to solve this. I create a ConverterFactory to resolve the needed types to create the converters. In the converter, I create new JsonObject and use Reflection to create the properties in the type, after this, I serialize the JsonObject so I can get the correct result.

Answer 1

Thank you for your question, but I did not found any difference between the serialization of Newtonsoft and System.Text.Json.

Perhabs you can provide an example in code to show us the problem directly. With your provided information I got with following code example the same results

static void Main(string[] args)
    {
        ItemCollection<Person> list = new ItemCollection<Person> {new Person(){ FirstName = "FirstName", Name = "Name"}};
        string jsonString = JsonSerializer.Serialize(list);
        Console.WriteLine(jsonString);


        string jsonString2 =Newtonsoft.Json.JsonConvert.SerializeObject(list);
        Console.WriteLine(jsonString2);

        Console.ReadLine();
    }

[{"Name":"Name","FirstName":"FirstName"}]

Answer 2

There is no built-in attribute corresponding to Newtonsoft's JsonObjectAttribute that will force a collection to be serialized as a JSON object. ¹ . And there is no public equivalent to IContractResolver that can be overridden to customize serialization metadata. Thus you will need to create a custom JsonConverter to serialize the properties of your ItemCollection<T> , such as the following:

[System.Text.Json.Serialization.JsonConverter(typeof(ItemCollectionJsonConverter))]
public partial class ItemCollection<T> : ICollection<T> {
    internal ItemCollection(List<T> items) { // I added this for use by the converter
        Items = items ?? throw new ArgumentNullException();
    }
    public ItemCollection() {
        Items = new List<T>();
    }
    public List<T> Items { get; set; }
    // Remainder omitted
}

public class ItemCollectionJsonConverter : JsonConverterFactory
{
    public override bool CanConvert(Type typeToConvert) => GetItemCollectionValueType(typeToConvert) != null;

    public override JsonConverter CreateConverter(Type type, JsonSerializerOptions options)
        => (JsonConverter)Activator.CreateInstance(typeof(ItemCollectionJsonConverterInner<>).MakeGenericType(GetItemCollectionValueType(type)!))!;

    static Type? GetItemCollectionValueType(Type type) =>
        (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(ItemCollection<>)) ? type.GetGenericArguments()[0] : null;

    class ItemCollectionJsonConverterInner<T> : JsonConverter<ItemCollection<T>>
    {
        class ItemCollectionDTO
        {
            public List<T>? Items { get; set; }
            // Add other properties here
        }
    
        public override ItemCollection<T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) =>
            // TODO: Decide whether to throw on null
            new ItemCollection<T>((JsonSerializer.Deserialize<ItemCollectionDTO>(ref reader, options)?.Items) ?? throw new JsonException());
        
        public override void Write(Utf8JsonWriter writer, ItemCollection<T> value, JsonSerializerOptions options) =>
            JsonSerializer.Serialize(writer, new ItemCollectionDTO { Items = value.Items }, options);
    }
}

Notes:

• I added the converter directly to ItemCollection<T> via attributes, but you could add it to JsonSerializerOptions.Converters if you prefer.

• Many serializers will not serialize collection properties. See eg XmlSerializer doesn't serialize everything in my class for another.

• Adding properties to collections isn't really a recommended practice; see Why not inherit from List<T>? for a discussion why.

Demo fiddle here .

---

¹ The list of all System.Text.Json serialization attributes is documented here .

Answer 3

just add object in Serialize method

 var jsonMessageBody = JsonSerializer.Serialize<object>(model);