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ELL Blog

ASP.NET Core Optional Json Fields

https://blog.elijahlopez.ca/posts/aspnet-optional-json-fields/ Elijah Lopez

Also featured in this article is enum to string converter.

ASP.NET Backend 

builder.Services.AddControllersWithViews(options => {
            options.Conventions.Add(new RouteTokenTransformerConvention(
                                         new SlugifyParameterTransformer()));

        }).AddJsonOptions(options => {
            options.JsonSerializerOptions.NumberHandling = JsonNumberHandling.AllowReadingFromString;
            options.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;               // JSON response is in  camelCase
            options.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;  // null not serialized
            options.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());                        // enums to string
            //  options.JsonSerializerOptions.IncludeFields = true;  // if you want to [de]serialize fields (i.e. get or set are omitted in the class)
        });

Client Side 

internal class Api {
    // Insert variables below here
    protected static HttpClient _client;
    protected static string BASE_URL = "http://10.0.2.2:5284/";
    // protected static string BASE_URL = "https://api.domain.com/";
    private static readonly ILogger _logger = typeof(Api).Log();
    private static JsonSerializerOptions _serializerOptions;

    static Api() {
        _client = new HttpClient();
        _serializerOptions = new() {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
        };
        _serializerOptions.Converters.Add(new JsonStringEnumConverter());
    }

    public string serializePayload<T>(T value) {
        return JsonSerializer.Serialize(value, _serializerOptions);
    }

    public T deserializePayload<T>(string payload) {
        return JsonSerializer.Deserialize<T>(payload, _serializerOptions);
    }
}

Generalized

Fields
Field Description
Always Property is always ignored
Never Property is always serialized and deserialized, regardless of IgnoreNullValues configuration
WhenWritingDefault Property is ignored only if it equals the default value for its type
WhenWritingNull Property is ignored if its value is null. This is applied only to reference-type properties and fields

For readers in a decade or so, see JsonIgnoreCondition


using System.Text.Json.Serialization;

namespace MyApi.Models;

public enum LoginErrors {
    InvalidEmail,
    TooManyRequests,
}

public class StartLoginResponse {
    [JsonConverter(typeof(JsonStringEnumConverter))]
    // this right here:
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
    public LoginErrors? Error { get; set; }
}