How to validate uploaded files by FluentValidation

Question

How can I validate uploaded files using FluentValidation?

      <input type="file" asp-for="Files" multiple />

Answer 1

your ViewModel must have public IList<IFormFile> Files { get; set; } :

    public class CustomViewModel
    {
        public IList<IFormFile> Files { get; set; }
        ...
    }

you must create a validator for IFormFile type as below:

    public class FileValidator : AbstractValidator<IFormFile>
    {
        public FileValidator()
        {
            RuleFor(x => x.Length).NotNull().LessThanOrEqualTo(100)
                .WithMessage("File size is larger than allowed");

            RuleFor(x => x.ContentType).NotNull().Must(x => x.Equals("image/jpeg") || x.Equals("image/jpg") || x.Equals("image/png"))
                .WithMessage("File type is larger than allowed");

               ...
        }
    }

now you can use FileValidator in your CustomValidator like this:

    public class CustomValidator : AbstractValidator<CustomViewModel>
    {
        public CustomValidator()
        {
            RuleForEach(x => x.Files).SetValidator(new FileValidator());
        }
    }