CODEWITHSUNDEEP
c#asp.net-core
user1574598
user1574598

Reputation: 3879

Set Null Property To Empty String With JsonConverter - System.Text.Json

I've been trying to deserialize some null paramaters with JsonSerializer and a custom JsonConverter from examples from posts I've seen about the subject, but its not working.

When I debug the NullToEmptyStringConverter is seems to be skipping the null parameter Version which I have deliberately set to null and just returning the string values that have a value. Then when you debug the deserialized object it is Version = null still.

public class NullToEmptyStringConverter : JsonConverter<string> {

    public override bool CanConvert(Type typeToConvert) {
        return typeToConvert == typeof(string);
    }

    public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) {
        string value = reader.GetString();

        if(value == null) {
            value = "";
        }
        return value;
    }

    public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options) {
        throw new NotImplementedException();
    }
}

I have added it to JsonSerializeOptions and added the attribute. Another thing I am confused about is why is the Read method being invoked for every parameter even though I have placed it above the Version property?

public class Application {

    [JsonPropertyName("version")]
    [JsonConverter(typeof(NullToEmptyStringConverter))]
    public string Version { get; set; }

    [JsonPropertyName("name")]
    public string Name { get; set; }

    [JsonPropertyName("description")]
    public string Description { get; set; }
}

Adding to the Converter

var options = new JsonSerializerOptions();
options.Converters.Add(new NullToEmptyStringConverter());

var config = JsonSerializer.Deserialize<ConfigRoot>(responseData.ToString(), options);

Upvotes: 3

Views: 2069

Answers (1)

Kirk Larkin
Kirk Larkin

Reputation: 93303

When I debug the NullToEmptyStringConverter is seems to be skipping the null parameter Version...

JsonConverter<T> includes a virtual property named HandleNull, which is false by default. Because of this, NullToEmptyStringConverter isn't used for null values. Override the getter and set it to return true, like this:

public override bool HandleNull => true;

...why is the Read method being invoked for every parameter even though I have placed it above the Version property?

In your example, you have the following line:

options.Converters.Add(new NullToEmptyStringConverter());

This registers NullToEmptyStringConverter as a global converter. Remove this registration and the converter will run only for the Version property, due to the [JsonConverter] attribute.

Upvotes: 4

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