Best way to only allow the setting of a property while deserializing a JsonProperty?

Question

I want to read in the id but I don't want it to be set once it's read in. The _processing variable is set while reading in the file and deserializing so it can be set. Is there a built-in more elegant way of handling this?

    private string _id;
    [JsonProperty(PropertyName = "id")]
    public string id
    {
        get { return _id; }
        set
        {
            if (_processing) // Only allow when reading the file
            {
                _id = value;
            }
        }
    }

Just use a private setter along with [JsonProperty]: https://stackoverflow.com/questions/4066947/private-setters-in-json-net — CodeCaster, Dec 30 '20 at 15:18

jjxtra · Accepted Answer · 2023-03-14T15:25:10.917

2

If you can use init only properties (since C#9.0) (https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-9.0/init):

[JsonProperty(PropertyName = "id")]
public string Id { get; init; }

If not...

private string _id;
[JsonProperty(PropertyName = "id")]
public string Id
{
    get { return _id; }
    set { _id ??= value; } // could also throw if _id is not null
}

Unrelated but helpful link on setting default property values if they are not found in the json: Default value for missing properties with JSON.net

edited Mar 14 '23 at 15:25

answered Dec 30 '20 at 14:54

jjxtra

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The non-init setter solution does however give the illusion to the caller that the ID can be set to another value. You can set it a second time, but nothing will happen. To prevent this you can also throw an InvalidOperationException. – Cédric Moers Dec 31 '20 at 12:42
Sure. It’s up to the implementor to decide – jjxtra Dec 31 '20 at 14:08

Ryan Wilson · Answer 2 · 2020-12-30T15:08:30.970

1

In C# 7.3 and earlier you can use the null-coalescing operator like so:

    set
    {
        _id = _id ?? value;
    }

In C# 8.0 and later you can do:

    set
    {
        _id ??= value;
    }

??= operator doesn't evaluate its right-hand operand if the left-hand operand evaluates to non-null.

edited Dec 30 '20 at 15:08

answered Dec 30 '20 at 15:02

Ryan Wilson

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This does however give the illusion to the caller that the ID can be set to another value. You can set it a second time, but nothing will happen. To prevent this you can also throw an InvalidOperationException. – Cédric Moers Dec 31 '20 at 12:42

Cédric Moers · Answer 3 · 2020-12-30T15:26:30.243

1

I think just using a private setter would work. Just don't call it again. You can also leave out the property name if these are the same.

    private string _id;
    [JsonProperty(PropertyName = "id")]
    public string id
    {
        get { return _id; }
        private set
        {
            _id = value;
        }
    }

or

    [JsonProperty]
    public string id { get; private set; }

edited Dec 30 '20 at 15:26

answered Dec 30 '20 at 15:05

Cédric Moers

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10

Best way to only allow the setting of a property while deserializing a JsonProperty?

3 Answers3