HAL

This project aims to bring a simple to use implementation of the Hypertext Application language.

Specification

• The formal specification is published as in IETF draft and can be found under https://tools.ietf.org/html/draft-kelly-json-hal-08.
• A more informal documentation can be found under http://stateless.co/hal_specification.html.
• The specification of HAL-Forms can be found here: https://rwcbook.github.io/hal-forms/

Usage

The project consists of multiple packages

1. HAL.Common which contains the Resource, Resource<T>, FormsResource, FormsResource<T> and Link implementations and the converters needed for serialization with System.Text.Json.
2. HAL.AspNetCore adds IResourceFactory, IFormFactory and ILinkFactory which can be used in your controllers to easily generate resources from your models. It also comes with a HalControllerBase class which can be used for all Controllers which return HAL.
3. HAL.AspNetCore.OData adds IODataResourceFactory and IODataFormFactory which can be used in your controllers to easily generate list endoints with paging from OData $filter, $skip and $top syntax.
4. Hal.Client.Net is a client library to consume HAL APIs in .Net applications. When using it, you should call app.Services.AddHalClientFactoy() to inject the IHalClientFactory which can then be resolved in your application.
5. Hal.Client.Angular/@wertzui/ngx-hal-client is a client library to consume HAL APIs in Angular applications. It exposes the HalClientModule which then provides the HalClient and a FormService.

Without OData support

In Program.cs

builder.Services
    .AddControllers() // or .AddMvc()
    .AddHal()
    .AddJsonOptions(o => // not neccessary, but creates a much nicer output
    {
        o.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault; 
    });

In your controller

[Route("[controller]")]
public class MyController : HalControllerBase
{
    private readonly IResourceFactory _resourceFactory;

    public Table(IResourceFactory resourceFactory)
    {
        _resourceFactory = resourceFactory ?? throw new ArgumentNullException(nameof(resourceFactory));
    }

    [HttpGet]
    [ApiConventionMethod(typeof(DefaultApiConventions), nameof(DefaultApiConventions.Get))]
    public ActionResult<IResource> GetList()
    {
        var models = new[]
        {
            new MyModelListDto {Id = 1, Name = "Test1"},
            new MyModelListDto {Id = 2, Name = "Test2"},
        };

        var result = _resourceFactory.CreateForListEndpoint(models, _ => "items", m => m.Id);

        return Ok(result);
    }

    [HttpGet("{id}")]
    public ActionResult<IResource<ModelFullDto>> Get(int id)
    {
        var model = new ModelFullDto { Id = id, Name = $"Test{id}", Description = "Very important!" };

        var result = _resourceFactory.CreateForGetEndpoint(model);

        return Ok(result);
    }

    // PUT, POST, ...
}

With OData support

In Program.cs with OData support

var modelBuilder = new ODataConventionModelBuilder();
modelBuilder.EntitySet<MyModelListDto>(typeof(MyModelListDto).Name);
builder.Services.AddSingleton(_ => modelBuilder.GetEdmModel());

builder.Services
    .AddControllers(options => // or .AddMvc()
    {
        options.OutputFormatters.RemoveType<ODataOutputFormatter>();
        options.InputFormatters.RemoveType<ODataInputFormatter>();
    })
    .AddOData()
    .AddHALOData()
    .AddJsonOptions(o => // not neccessary, but creates a much nicer output
    {
        o.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingDefault; 
    });
}

var app = builder.Build();

app.UseRouting();

// ...

app.UseEndpoints(_ => { });
app.MapControllers();
}

In your controller with OData support

[Route("[controller]")]
public class MyController : HalControllerBase
{
    private readonly IODataResourceFactory _resourceFactory;

    public Table(IODataResourceFactory resourceFactory)
    {
        _resourceFactory = resourceFactory ?? throw new ArgumentNullException(nameof(resourceFactory));
    }

    [HttpGet]
    [ApiConventionMethod(typeof(DefaultApiConventions), nameof(DefaultApiConventions.Get))]
    public ActionResult<Resource> GetList(
            // The SwaggerIgnore attribute and all parameters beside the options are just here to give you a nice swagger experience.
            // If you do not need that, you can remove everything except the options parameter.
            // If you are using RESTworld, you can also remove everything except the options parameter, because there is a custom Swagger filter for that.
            [SwaggerIgnore] ODataQueryOptions<TEntity> options,
            [FromQuery(Name = "$filter")] string? filter = default,
            [FromQuery(Name = "$orderby")] string? orderby = default,
            [FromQuery(Name = "$top")] long? top = default,
            [FromQuery(Name = "$skip")] long? skip = default)
    {
        var models = new[]
        {
            new MyModelListDto { Id = 1, Name = "Test1" },
            new MyModelListDto { Id = 2, Name = "Test2" },
        };

        // Apply the OData filtering
        models = options.Apply(models.AsQueryable()).Cast<MyModelListDto>().ToArray()

        var result = _resourceFactory.CreateForOdataListEndpointUsingSkipTopPaging(models, _ => "items", m => m.Id, options);

        return Ok(result);
    }

    // GET, PUT, POST, ...
}