Validate fields which are only provided in API JSON body using .NET Data Annotations

Question

I am working on .NET Core Web API project, I have few data models and implemented data annotations.

While updating user profile, user can enter all fields or only some fields in API JSON body.

How do I check and apply data annotation only if specific field is provided in API JSON.

Note: User Id cannot be updated , it is only for reference.

In below model, I have 4 fields, only User Id is mandatory to be provided in API JSON rest all fields are optional to be entered in JSON while updating.

Conditions:

If any field is provided in API JSON, then it should not be NULL or empty value
If any field is not provided except user_id, it can ignore and do check null annotation for the fields provided.

I know we can validate by removing Required() for each column and validate manually.

Example:

JSON1

{
  "user_id":"XYZ-123"
}

Expected Result: Since no optional fields provided, it should Accept and pass validation

Example:

JSON2

{
  "user_id":"XYZ-123",
  "work_phone":"+91-987654320"
}

Expected Result: Since only work phone is provided, it should Accept and pass validation

Data Model:

public class UserDetails
    {

        [Required(AllowEmptyStrings = false, ErrorMessage = "The user_id field is required.")]
        [JsonProperty("user_id")]
        public string? UserId{ get; set; }

        [Required(AllowEmptyStrings = false, ErrorMessage = "The home_phone field is required.")]
        [JsonProperty("home_phone")]
        public string? HomePhone { get; set; }

        [Required(AllowEmptyStrings = false, ErrorMessage = "The work_phone field is required.")]
        [JsonProperty("work_phone")]
        public string? WorkPhone { get; set; }

        [Required(AllowEmptyStrings = false, ErrorMessage = "The mobile_phone field is required.")]
        [JsonProperty("mobile_phone")]
        public string? MobilePhone { get; set; }
}

Haven't tried this, but may be you can use `RegularExpression(@"^[\w\d][\w\d-+]*$")` instead of `Required`. Change the regular expression as needed. — prinkpan, Oct 05 '22 at 18:08

score 0 · Answer 1 · answered Oct 06 '22 at 03:04

I don't think it's possible if you don't get rid of the Required() attribute. Required is a data annotation for the view. The view will require it to have a value prior to accepting a form post.

If you want it to be a must in some case, you can refer to this post. The RequiredIf() attribute used by DrCopyPaste's answer might help you.

Validate fields which are only provided in API JSON body using .NET Data Annotations

1 Answers1