Harvzor.Optional.SystemTextJson 0.0.5

Harvzor.Optional

NuGet Package	Version
Harvzor.Optional
Harvzor.Optional.SystemTextJson
Harvzor.Optional.NewtonsoftJson

The problem

// The JSON would normally come from some external data source:
string json = "{}";

Foo foo = JsonSerializer.Deserialize<Foo>(json);

// This will print an empty string because C# will hydrate the model with the default value.
// There's no way to check if the model used a default value.
Console.WriteLine(foo.MyProperty); // ""    

public class Foo
{
    public string MyProperty { get; set; }
}

In the above example, you could make the string nullable (with string?), but now you're explicitly saying that null is value you want to accept. And then you might actually want to explicitly allow null values, but then run into the same issue where you're not sure if the original JSON had the value as null, or if it was just undefined.

The solution: Optional<T>

Basic example

You can use Optional<T> to know if a property or variable has been explicitly instantiated:

using Harvzor.Optional;

Foo foo = new Foo
{
    DefinedProperty = "Bar"
};

Console.WriteLine(foo.DefinedProperty.IsDefined); // True
Console.WriteLine(foo.UndefinedProperty.IsDefined); // False

// Now I can check if a value was explicitly instantiated:
if (foo.DefinedProperty.IsDefined)
    Console.WriteLine(foo.DefinedProperty.Value); // "Bar" 
    
if (foo.UndefinedProperty.IsDefined)
    Console.WriteLine(foo.UndefinedProperty.Value); // Won't print as the value wasn't explicitly instantiated.

Console.WriteLine(foo.UndefinedProperty.Value); // Will print the default value.

public class Foo
{
    public Optional<string> DefinedProperty { get; set; }
    public Optional<string> UndefinedProperty { get; set; }
}

Use it with JSON

This example uses System.Text.Json, but it's pretty similar to Newtonsoft:

using System.Text.Json;
using Harvzor.Optional;

JsonSerializerOptions jsonSerializerOptions = new JsonSerializerOptions();
jsonSerializerOptions.Converters.Add(new Harvzor.Optional.SystemTextJson.OptionalJsonConverter());

// The JSON would normally come from some external data source:
string json = "{\"DefinedProperty\":\"Bar\"}";

Foo foo = JsonSerializer.Deserialize<Foo>(json, jsonSerializerOptions)!;

Console.WriteLine(foo.DefinedProperty.IsDefined); // True
Console.WriteLine(foo.UndefinedProperty.IsDefined); // False

// Now I can check if a value was defined before I try using it:
if (foo.DefinedProperty.IsDefined)
    Console.WriteLine(foo.DefinedProperty.Value); // "Bar" 
    
if (foo.UndefinedProperty.IsDefined)
    Console.WriteLine(foo.UndefinedProperty.Value); // Won't print as the value wasn't defined.

public class Foo
{
    public Optional<string> DefinedProperty { get; set; }
    public Optional<string> UndefinedProperty { get; set; }
}

Harvzor.Optional.SystemTextJson

Use in an API

To use it in your controller models, simply register in your startup:

services
    .AddControllers()
    .AddJsonOptions(options =>
    {
        options.JsonSerializerOptions.Converters.Add(new Harvzor.Optional.SystemTextJson.OptionalJsonConverter());
    });

Swagger support

If you're using Swashbuckle Swagger, you'll also need to tell it how your types should look:

services.AddSwaggerGen(options =>
{ 
    options.MapType<Optional<string>>(() => new OpenApiSchema
    {
        Type = "string"
    });
    
    options.MapType<Optional<bool>>(() => new OpenApiSchema
    {
        Type = "boolean"
    });
});

You can see what basic types are available here: https://swagger.io/docs/specification/data-models/data-types/

Harvzor.Optional.NewtonsoftJson

... docs to come ...

Releasing

Manual release

1. Get an API key from https://www.nuget.org/account/apikeys

docker-compose build --build-arg version="{version}" push-nuget
docker-compose run --rm push-nuget --api-key {key}