Using System.Text.Json to ignore default values for bool data type, only

Question

Is there a way at a global level to ignore all and only bools when returning false with System.Text.Json?

I know there's this global condition, but I still need other default values to return.

JsonSerializerOptions options = new()
           {
                DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault
            };

Ideally would not like to add the following to all propeties individually.. [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]

Answer 1

You can't use a custom JsonConverter for all types, because then you'll have to reinvent the wheel to serialize whole thing. You also can't use a JsonConverter<bool> (or <bool?>), because you have to write a value in its Write() method.

So register a DefaultJsonTypeInfoResolver with a custom Modifiers action that only serializes bools when their value equals true:

JsonSerializerOptions options = new()
{
    TypeInfoResolver = new DefaultJsonTypeInfoResolver
    {
        Modifiers =
        {
            jsonTypeInfo =>
            {
                foreach (var p in jsonTypeInfo.Properties)
                {
                    if (p.PropertyType == typeof(bool) || p.PropertyType == typeof(bool?))
                    {
                        p.ShouldSerialize = (containingObject, propertyValue) =>
                        {
                            return propertyValue as bool? == true;
                        };
                    }
                }
            }
        }
    }
};

From MS Learn: Customize a JSON contract. Works since .NET 7.