C#•2mo ago

How is Modelstate.IsValid triggered?

Hello! I am reading this tutorial on how DTO's can be implemented with API's: https://dev.to/moe23/net-6-automapper-data-transfer-objects-dtos-49e The process in this tutorial seems normal and you can easily follow along. There are only 2 things I have my questions about: 1. The Driver class in this tutorial has no DataAnnotations (see first codeblock). How come the Modelstate.IsValid can be triggered in codeblock 2?

namespace SampleMapper.Models;

public class Driver
{
    public Guid Id { get; set; }
    public string FirstName { get; set; } = "";
    public string LastName { get; set; } = "";
    public int DriverNumber { get; set; }
    public DateTime DateAdded { get; set; }
    public DateTime DateUpdated { get; set; }
    public int Status { get; set; }
    public int WorldChampionships { get; set; }
}

namespace SampleMapper.Models;

public class Driver
{
    public Guid Id { get; set; }
    public string FirstName { get; set; } = "";
    public string LastName { get; set; } = "";
    public int DriverNumber { get; set; }
    public DateTime DateAdded { get; set; }
    public DateTime DateUpdated { get; set; }
    public int Status { get; set; }
    public int WorldChampionships { get; set; }
}

2. How does Modelstate.IsValid get triggered when a Dto is passed but it gets mapped to an entity?

[HttpPost]
    public IActionResult CreateDriver(DriverCreationDto data)
    {
        var _driver = _mapper.Map<Driver>(data);

        if(ModelState.IsValid)
        {
            drivers.Add(_driver);

            return CreatedAtAction("GetDriver", new {_driver.Id}, data);
        }

        return new JsonResult("Something went wrong") {StatusCode = 500};
    }

[HttpPost]
    public IActionResult CreateDriver(DriverCreationDto data)
    {
        var _driver = _mapper.Map<Driver>(data);

        if(ModelState.IsValid)
        {
            drivers.Add(_driver);

            return CreatedAtAction("GetDriver", new {_driver.Id}, data);
        }

        return new JsonResult("Something went wrong") {StatusCode = 500};
    }

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39 Replies

Anton•2mo ago

If it can't bind json to that object. Like if it can't parse a string as a datetime. Or if the json is invalid in some way too, I think. Like if you pass tru instead of true.

△ electronic heartbreak.•2mo ago

Would not the _mapper function then crash?

Anton•2mo ago

No the parameter will have the defaults for those properties then But that cab only happen if you turn off the filter that shortcircuits this in MVC generally, it would return a response automatically at that point Or maybe it will just be null? not sure the mapper has nothing to do with ModelState

△ electronic heartbreak.•2mo ago

I have a little hard time to understand this. thats correct

Anton•2mo ago

well just try passing some garbage json with the default mvc settings and see what error you get it won't even get to your code

△ electronic heartbreak.•2mo ago

oh like that.

Anton•2mo ago

But it will ignore extra fields, I'm pretty sure and if you don't provide a value for a property, it will initialize it to null

△ electronic heartbreak.•2mo ago

if we check the Driver model for example in the code above. Lets say the driver number should be between 1 and 5 and the DTO contains 0? then it should fail

Anton•2mo ago

no it won't handle that automatically unless you do data annotations and enable them, I think they aren't on by default

△ electronic heartbreak.•2mo ago

yes data annotations should be added. But you should not add data annotations on DTO's

Anton•2mo ago

Well then you won't be using MVC's system for validation which isn't good in the first place, to be fair data annotations are pretty primitive

△ electronic heartbreak.•2mo ago

Since the DTO comes in at the controller. you would 'normally' validate the object that comes in.

Anton•2mo ago

well one thing for certain

△ electronic heartbreak.•2mo ago

i do say that adding basic validation, like required or min/max length would be OK.

Anton•2mo ago

mapping typically never does any validation

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How is Modelstate.IsValid triggered?