How to pass multiple parameters to a get method in ASP.NET Core

Question

You also can use this:

// GET api/user/firstname/lastname/address
[HttpGet("{firstName}/{lastName}/{address}")]
public string GetQuery(string id, string firstName, string lastName, string address)
{
    return $"{firstName}:{lastName}:{address}";
}

Note: Please refer to the answers from metalheart and Mark Hughes for a possibly better approach.

Why not using just one controller action?

public string Get(int? id, string firstName, string lastName, string address)
{
   if (id.HasValue)
      GetById(id);
   else if (string.IsNullOrEmpty(address))
      GetByName(firstName, lastName);
   else
      GetByNameAddress(firstName, lastName, address);
}

Another option is to use attribute routing, but then you'd need to have a different URL format:

//api/person/byId?id=1
[HttpGet("byId")] 
public string Get(int id)
{
}

//api/person/byName?firstName=a&lastName=b
[HttpGet("byName")]
public string Get(string firstName, string lastName, string address)
{
}

To parse the search parameters from the URL, you need to annotate the controller method parameters with [FromQuery], for example:

[Route("api/person")]
public class PersonController : Controller
{
    [HttpGet]
    public string GetById([FromQuery]int id)
    {

    }

    [HttpGet]
    public string GetByName([FromQuery]string firstName, [FromQuery]string lastName)
    {

    }

    [HttpGet]
    public string GetByNameAndAddress([FromQuery]string firstName, [FromQuery]string lastName, [FromQuery]string address)
    {

    }
}

I would suggest to use a separate dto object as an argument:

[Route("api/[controller]")]
public class PersonController : Controller
{
    public string Get([FromQuery] GetPersonQueryObject request)
    {
        // Your code goes here
    }
}

public class GetPersonQueryObject 
{
    public int? Id { get; set; }
    public string Firstname { get; set; }
    public string Lastname { get; set; }
    public string Address { get; set; }
}

Dotnet will map the fields to your object.

This will make it a lot easier to pass through your parameters and will result in much clearer code.