.NET NewtonSoft JSON deserialize list with auto-increment index

Question

My current situation is I have a json file

[
    {
        "first_name" : "Foo",
        "last_name" : "Bar",
        "gender" : 0
    },
    {
        "first_name" : "FooFoo",
        "last_name" : "BarBar",
        "gender" : 1
    }
]

and a Person class:

class Person
{
    public Id { get; private set; }
    public string FirstName;
    public string LastName;
    public int Gender; 
}

and I'm using the deserializer like this:

JArray.ToObject<List<Person>>();

or the equivalent:

JsonConvert.DeserializeObject<List<Person>>(jsonstr, ...)

although there is non in the json object itself, in the Person class there is a "Id" field and I need it to have increasing values according to the Person's position in the list.

The reason I can't make Id public property and set it after deserialize is because, it's an Id it should NOT be editable and I think is bad programming.

I've heard of JsonConverters. Is this achievable using them? I needed some help. Summing up I needed a way to deserialize Json arrays into objects' lists and automatically set them auto incrementing Ids.

Well then, thank you for your time.

Answer 1

You don't need to change anything in the deserialization process, you can simply do something in the constructor of the class:

static int NextId = 0;

public Person() 
{
     Id = NextId++;
}

And, yes, you definitely don't want your Id to be editable. A good pattern here would be

public int Id { get; private set;}

You can also put a [JsonIgnore] attribute on Id. This will mean this will not be assigned to.

[JsonIgnore]
public int Id { get; private set;}

To reset IDs

public static void ResetNextId(int startId)
{
    NextId = startId;
}

Person.ResetNextId(0);

There is also an [OnDeserialized] attribute you can apply to a procedure on the object to assign properties after the object has been deserialization.

[OnDeserialized]
public void OnDeserialized(StreamingContext context)
{
     // Do stuff
}