`IValidatableObject` validation executed on relationship objects

[Tommy228]

DESCRIPTION

When I use an object implementing IValidatableObject on a relationship with linkage data only, then the validation is still executed.

This bug looks similar to #671 which had the same issue when using the [Required] attribute.

STEPS TO REPRODUCE

Consider the following models

[Resource]
public class Library : Identifiable<int>, IValidatableObject
{
    [Attr, Required] public string? Name { get; set; }

    [HasMany] public ICollection<Book> Books { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        // Should never happen as we have the [Required] attribute
        // However, this is still called when used on a relationship
        if (Name == null)
        {
            yield return new ValidationResult("Name is mandatory");
        }
    }
}

[Resource]
public class Book : Identifiable<int>
{
    [Attr] public string? Name { get; set; }

    [HasOne] public Library Library { get; set; }
}

First, create a library

{
    "data": {
        "type": "libraries",
        "attributes": {
            "name": "Test library"
        },
        "relationships": {
            "books": {
                "data": []
            }
        }
    }
}

Then, create a book and associate it with the created library.

{
    "data": {
        "type": "books",
        "attributes": {
            "name": "Test book"
        },
        "relationships": {
            "library": {
                "data": { 
                    "type": "libraries",
                    "id": "1" 
                }
            }
        }
    }
}

EXPECTED BEHAVIOR

The book is created.

ACTUAL BEHAVIOR

The custom validation code from Library is executed, causing this error

{
    "links": {
        "self": "http://localhost:5000/v1/books"
    },
    "errors": [
        {
            "id": "5d84f0da-0432-49e4-9214-6e4476fd35d6",
            "status": "422",
            "title": "Input validation failed.",
            "detail": "Name is mandatory",
            "source": {
                "pointer": "/data/relationships/library/data"
            }
        }
    ]
}

VERSIONS USED

• JsonApiDotNetCore version: 5.0.3
• ASP.NET Core version: 6.0.301
• Entity Framework Core version: 6.0.10
• Database provider: pgsql

[bkoelman]

Hi @Tommy228, thanks for the detailed report.

To fix this, your implementation of IValidatableObject needs to do something similar to https://github.com/json-api-dotnet/JsonApiDotNetCore/blob/master/src/JsonApiDotNetCore/Configuration/JsonApiValidationFilter.cs.

The problem is that JSON:API uses partially filled objects in post/patch resource endpoints, or even objects with only Id populated. To distinguish between "this incoming property is invalid" vs "this property was never sent, so it contains a default value", inject and inspect ITargetedFields to choose what validation is actually needed.

I don't think there's anything we can fix in JADNC to solve this, therefore I don't think this is a bug.

[Tommy228]

Hi @bkoelman, I tried the suggested solution with ITargetedFields and it indeed works, so I guess we can close this. Thanks for your time.