How to validate model in .Net Core 3.1 in console app when the model contains another class's object as a property using DataAnnotations?

Question

I have the following request model:

public class VisitRequest
    {
        public ProviderInfo Provider { get; set; }

        [Required]
        [MaxLength(64)]
        public string PayerId { get; set; }
    }

And i have the custom class as follows:

 public class ProviderInfo
    {
        [Required]
        [MaxLength(15)]
        public string TaxId { get; set; }

        [Required(ErrorMessage = " Qualifier is required.")]
        [MaxLength(15)]
        public string NPI { get; set; }
    }

I am currently using ValidationContext to do the model validations:

var visitData = JsonConvert.DeserializeObject<VisitRequest>(jsonString);
var vc = new ValidationContext(visitData);
var errorResults = new List<ValidationResult>();
var isValid = Validator.TryValidateObject(visitData, vc, errorResults, true);

My demo json request is as follows:

{
'Member': {
  'Qualifier': 'MedicaidID',
  'Identifier': '100'
  },                
  'ExternalVisitID': '123456789',
}

Now I am receiving the ErrorMessage in ErrorResult as:

PayerId is required.

But I am not getting the validations of the custom class. How to implement this in .Net Core Console application ? I am quite new to.Net Core so any help would be appreciated.Thanks!

---

UPDATE:

I followed the answer given by @John H but still there is one issue.

If my request is:

'Provider' : {
      'TaxId' : null
}

it will work fine, because it is able to identify that this is the type ProviderInfo object.

But if my request does not contain any info regarding the Provider:

{
'ExternalVisitID': '123456789',
'EVVMSID': '100', 
}

then it is not able to validate the object.

Answer 1

In brief, this doesn't work because TryValidateObject doesn't support the validation of complex nested types. This was also an issue for the .NET Framework version of this type, and @reustmd created a NuGet Package to solve the problem. Unfortunately, it doesn't support .NET Core, but I found there is a package forked from this which does. From the readme:

Installation

Available as NuGet-Package dataannotationsvalidator :

Install-Package dataannotationsvalidator

Usage

See file DataAnnotationsValidator/DataAnnotationsValidator.Tests/DataAnnotationsValidatorTests.cs

Short example:

var validator = new DataAnnotationsValidator.DataAnnotationsValidator();

var validationResults = new List<ValidationResult>();

validator.TryValidateObjectRecursive(modelToValidate, validationResults);

This should solve your problem.

As an aside, I also found this proposal discussing adding this functionality to .NET. If you're interested in a technical design discussion of that proposal, there is a video posted by the .NET Foundation discussing it.

Update

For your scenario above, I've installed the above package, changed the VisitRequest class to make the provider required

public class VisitRequest
{
    [Required]
    public ProviderInfo Provider { get; set; }

    [Required]
    [MaxLength(64)]
    public string PayerId { get; set; }
}

and then ran the following:

var jsonString = @"{
    ""ExternalVisitID"": ""123456789"",
    ""EVVMSID"": ""100""
}";

var modelToValidate = JsonConvert.DeserializeObject<VisitRequest>(jsonString);

var validator = new DataAnnotationsValidator.DataAnnotationsValidator();

var validationResults = new List<ValidationResult>();

validator.TryValidateObjectRecursive(modelToValidate, validationResults);

foreach (var item in validationResults)
{
    Console.WriteLine(item.ErrorMessage);

    foreach (var memberName in item.MemberNames)
    {
        Console.WriteLine($"\t{memberName}");
    }
}

which produces output of:

The Provider field is required.
    Provider
The PayerId field is required.
    PayerId

If you're wanting to list each field of a provider that's missing individually, even though that part of the JSON is empty, I think you'll have to fork the NuGet package and make those changes. But this is probably a reason why .NET hasn't supported this functionality out of the box, because people have different expectations for how it should behave.