Can System.Text.Json.JsonSerializer serialize collections on a read-only property?

问题

I'm having trouble getting the new System.Text.Json to deserialize collections stored on read-only properties.

Consider these classes:

public class SomeItem {
    public string Label { get; set; }
}

public class SomeObjectWithItems {

    public string Label { get; set; }

    // Note this property is read-only but the collection it points to is read/write
    public ObservableCollection<SomeItem> Items { get; }
        = new ObservableCollection<SomeItem>();
}

Here's the JSON:

{
  "Label": "First Set",
  "Items": [
    {
      "Label": "Item 1"
    },
    {
      "Label": "Item 2"
    },
    {
      "Label": "Item 3"
    },
    {
      "Label": "Item 4"
    }
  ]
}

Here's the code I'm running...

var json = ...;
var obj = JsonSerializer.deserialize<SomeObjectWithItems>(json);
Debug.WriteLine($"Item Count for '{obj.label}': {obj.Items.Count}");

The above outputs the following:

Item Count for 'First Set': 0

If I change Items to be read/write, then it works, but so many of our models have read-only properties that hold mutable collections so I'm wondering if we can even use this.

Note: Json.NET handles this correctly, internally calling the 'Add' method on the existing collection rather than creating a new one, but I don't know how to achieve that outside of writing custom converters for all the classes we have defined.

回答1:

This is by design for collections that don't have a setter. To avoid issues with adding to pre-populated collections (that the serializer doesn't instantiate) the deserializer uses "replace" semantics which requires the collection to have a setter.

Source: https://github.com/dotnet/corefx/issues/41433

There is currently an open issue for Support adding to collections if no setter

https://github.com/dotnet/corefx/issues/39477

My recommendation is continue to use Json.NET in this case unless you want to write a customer converter.

来源：https://stackoverflow.com/questions/59748093/can-system-text-json-jsonserializer-serialize-collections-on-a-read-only-propert

标签

json

json.net

system.text.json