parr_api/PARR.API/Validators/DistributeRequestValidator.cs

using FluentValidation;
using PARR.API.Contracts.V1.Requests;
using PARR.DAL.Services.Interfaces;

namespace PARR.API.Validators
{
    public class DistributeRequestValidator : AbstractValidator<DistributeRequest>
    {
        private readonly IApplicationsInWorkService applicationsInWorkService;

        public DistributeRequestValidator(IApplicationsInWorkService applicationsInWorkService)
        {
            this.applicationsInWorkService = applicationsInWorkService;


            RuleFor(t => t.ApplicationInWorkId).NotEmpty().MustAsync(async (entity, value, c) =>
            {
                var appInWork = await applicationsInWorkService.GetAsync(value);

                return appInWork != null;
            }).WithMessage("Недопустимое значение");
        }
    }
}