ASP.NET Core WebAPI FromBody attribute is not validating object non-reference fields

Question

I have action Create inside my controller:

[HttpPost]
public async Task<IActionResult> Create([FromBody] PostCreate createDto)
{
    // do something with Create DTO
}

It accepts DTO for Post creation (parameter is marked with [FromBody] attribute). That DTO has 2 properties: string(reference type) Content property and System.Guid(value type) property:

public class PostCreate
{
    [Required(ErrorMessage = "content is required")]
    public string Content { get; set; }

    [Required(ErrorMessage = "blog id is required")]
    public Guid BlogId { get; set; }
}

The issue is that when i sending valid object everything is work just fine (both Content and BlodId properties are initialized). But when i sending empty object it checking only Content property:

{
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "One or more validation errors occurred.",
    "status": 400,
    "traceId": "|dfcd1687-4a0b9320d8411509.",
    "errors": {
        "Content": [
            "content is required"
        ]
    }
}

If i provide value only for Content property it passes validation and BlogId value is "00000000-0000-0000-0000-000000000000" or Guid.Empty. The same thing for all non reference types (e.g. for int value is 0).

Question 1: "Why it behaves like this?" Question 2: "How to make default validation check non-reference types for emptiness?"

UPDATE (useful walkaround):

As Octavio Armenta pointed out in the answer: "You will probably have to create a custom attribute that checks the emptiness of a Guid. If you want to use an attribute.". I did it like this:

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter)]
public class NotEmptyAttribute : ValidationAttribute
{
    public const string DefaultErrorMessage = "The {0} field must not be empty";

    public NotEmptyAttribute()
        : base(DefaultErrorMessage) { }

    public override bool IsValid(object value)
    {
        if (value == null)
        {
            return true;
        }

        return value switch
        {
            Guid guid => guid != Guid.Empty,
            // other non-reference types checks
            _ => true
        };
    }
}

Note: The above code snippet uses a switch expression that is only available since C# 8. You can also use a regular switch statement.

Octavio Armenta Octavio Armenta · Accepted Answer · 2020-07-17T19:36:55

The default value of a Guid is Guid.Empty, which passes validation of RequiredAttribute. You will probably have to create a custom attribute that checks the emptiness of a Guid. If you want to use an attribute.

ASP.NET Core WebAPI FromBody attribute is not validating object non-reference fields

2 Answers