NET Core: Filtering with HttpGet - .net-core

Question

I would like to filter a list of vehicles, by their makeId using httpGet. The URL I would expect to use is:
https://localhost:5001/api/vehicle?makeId=2
Below, I will define the DTO and controller methods I used for this task:
FilterDto
public class FilterDTO
{
public int? MakeId { get; set; }
}
Below are the 2 HTTPGet methods in my controller class. I expect the first method to be called.
[HttpGet]
public async Task<IEnumerable<VehicleDTO>> Get(FilterDTO filterDto)
{
var filter = _mapper.Map<Filter>(filterDto);
var vehicles = await _vehicleRepository.GetAll(filter);
return _mapper.Map<IEnumerable<VehicleDTO>>(vehicles);
}
[HttpGet("{id}")]
public async Task<ActionResult<VehicleDTO>> Get(long id)
{
var vehicle = await _vehicleRepository.GetWithRelated(id);
if (vehicle == default)
{
return BadRequest("Vehicle not found");
}
var result = _mapper.Map<VehicleDTO>(vehicle);
return Ok(result);
}
With the above code, when I call the URL above, in Postman I get a 400 Error, saying "The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. Path: $ | LineNumber: 0 | BytePositionInLine: 0."
I get the same result for https://localhost:5001/api/vehicle
If I change the first Get method like below, I am able to get a response:
[HttpGet]
public async Task<IEnumerable<VehicleDTO>> Get(int? makeId)
{
var filter = new Filter { MakeId = makeId};
var vehicles = await _vehicleRepository.GetAll(filter);
return _mapper.Map<IEnumerable<VehicleDTO>>(vehicles);
}
After this (lengthy) introduction, my questions are:
Why does HttpGet support 'int?' but not the data transfer object 'FilterDto'?
Should I be using a different verb instead of HttpGet?
I might have to filter in the future for some other types (say customerId). Is there any way I can change the method to support custom objects, like FilterDto, ideally without changing the verb?

Answer 1

Change your code as follow:
[HttpGet]
public async Task<IEnumerable<VehicleDTO>> Get([FromQuery] FilterDTO filterDto)
{
var filter = _mapper.Map<Filter>(filterDto);
var vehicles = await _vehicleRepository.GetAll(filter);
return _mapper.Map<IEnumerable<VehicleDTO>>(vehicles);
}
and call it like:
baseUrl/Controller/Get?MarkId=1

Answer 2

Take a look at the docs.
Basically the primitive types are supported, but the controller has no idea how to convert your web request data into C# object. You need to explicitly tell it how you want this custom object to be created out of web request.

Answer 3

You may have in mind that HttpGet methods are only able to receive primitiveTypes (string, int, short, datetime -using a specific format-) because the arguments are being sent through query string, for example:
myAddres.com/api/mymethod?id=5&filter1=value1&filter2=value2
Having this consideration in mind you'll notice there's no way to send any object because you need to use a json or another notation, remember querystring has a limit and because of that is better using "argument=value" notation.
On the other hand PUT and POST are able to send their data through a "body" property where you may use a json notation and this way you may create almost any object on your Backend side.
If you need to use an object as an argument it is a better idea using POST or PUT (better POST than PUT).