How to use Hashids with AutoMapper

#dotnet #csharp

Why to use Hashids?

Hashids helps you to convert a number Id to a string, this can make your app a little more secure hiding the actual id or related key of your DB when the data is requested by an API.

Why is useful ValueConverter of AutoMapper?

ValueConverter can handle the convertion inside te .Map<TDestination>(source) method allowing you put the convertion logic in only one place.

The model

//Model of your data
public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int ClassEnrollmentId { get; set; }
}

//Data Transfer Object (DTO) for your client
public class StudentDto
{
    public string Id { get; set; }
    public string Name { get; set; }
    public string ClassEnrollmentId { get; set; }
}

The configuration

After you install the nuget packages:

Install-Package hashids.net
Install-Package AutoMapper.Extensions.Microsoft.DependencyInjection

Add the following code to the Program.cs to use hashids and AutoMapper with dependency injection, if you prefer to use a class Startup you have to put it on the ConfigureServices method.

builder.Services.AddSingleton<IHashids>(_ => 
new Hashids("this is my salt"));
// Optional, you can set the length of the string 
// new Hashids("this is my salt", [the number you want])

builder.Services.AddAutoMapper(typeof(AutoMapperProfile));

AutoMapperProfile

using AutoMapper; // To use the Profile class

public class AutoMapperProfile: Profile
{
    public AutoMapperProfile()
    {
        //This configuration convert the int property who saves Ids to hash string
        CreateMap<Student, StudentDto>()
            .ForMember(d => d.Id, opt => opt.ConvertUsing<HashFormatter, int>())
            .ForMember(d => d.ClassEnrollmentId, opt => opt.ConvertUsing<HashFormatter, int>());


        //This configuration makes the oposite from the above configuration
        CreateMap<StudentDto, Student>()
            .ForMember(d => d.Id, opt => opt.ConvertUsing<IntFromHash, string>())
            .ForMember(d => d.ClassEnrollmentId, opt => opt.ConvertUsing<IntFromHash, string>());
    }
}

Convertion classes

using AutoMapper; //To use IValueConverter interface
using HashidsNet; //To use IHashids interface

public class HashFormatter : IValueConverter<int, string>
{
    private readonly IHashids hashids;

    public HashFormatter(IHashids hashids)
    {
        this.hashids = hashids;
    }

    public string Convert(int source, ResolutionContext context)
    {
        return hashids.Encode(source);
    }
}
public class IntFromHash : IValueConverter<string, int>
{
    private readonly IHashids hashids;

    public IntFromHash(IHashids hashids)
    {
        this.hashids = hashids;
    }

    public int Convert(string source, ResolutionContext context)
    {
        return hashids.DecodeSingle(source);
    }
}

How to use it

In a controller only have to inject AutoMapper and call the .Map method like this.

public class StudentstController : ControllerBase
{
    private readonly IMapper mapper;

    public StudentstController(IMapper mapper)
    {
        this.mapper = mapper;
    }

    [HttpGet]
    public IActionResult Get()
    {
        //Summaries is the data as List<Student>
        return Ok(mapper.Map<List<StudentDto>>(Summaries));
    }
}

Result

Data without hash

[
  {
    "id": 1,
    "name": "Juan",
    "classEnrollmentId": 2
  },
  {
    "id": 2,
    "name": "Pedro",
    "classEnrollmentId": 1
  }
]

Data with hash

[
  {
    "id": "NV",
    "name": "Juan",
    "classEnrollmentId": "6m"
  },
  {
    "id": "6m",
    "name": "Pedro",
    "classEnrollmentId": "NV"
  }
]