ersatztv/ErsatzTV.Application/MediaCollections/Commands/DeleteMultiCollectionHandler.cs

using System.Threading;
using System.Threading.Tasks;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Infrastructure.Data;
using ErsatzTV.Infrastructure.Extensions;
using LanguageExt;
using Microsoft.EntityFrameworkCore;

namespace ErsatzTV.Application.MediaCollections.Commands
{
    public class DeleteMultiCollectionHandler : MediatR.IRequestHandler<DeleteMultiCollection, Either<BaseError, Unit>>
    {
        private readonly IDbContextFactory<TvContext> _dbContextFactory;

        public DeleteMultiCollectionHandler(IDbContextFactory<TvContext> dbContextFactory) =>
            _dbContextFactory = dbContextFactory;

        public async Task<Either<BaseError, Unit>> Handle(
            DeleteMultiCollection request,
            CancellationToken cancellationToken)
        {
            await using TvContext dbContext = _dbContextFactory.CreateDbContext();

            Validation<BaseError, MultiCollection> validation = await MultiCollectionMustExist(dbContext, request);
            return await validation.Apply(c => DoDeletion(dbContext, c));
        }

        private static Task<Unit> DoDeletion(TvContext dbContext, MultiCollection multiCollection)
        {
            dbContext.MultiCollections.Remove(multiCollection);
            return dbContext.SaveChangesAsync().ToUnit();
        }

        private static Task<Validation<BaseError, MultiCollection>> MultiCollectionMustExist(
            TvContext dbContext,
            DeleteMultiCollection request) =>
            dbContext.MultiCollections
                .SelectOneAsync(c => c.Id, c => c.Id == request.MultiCollectionId)
                .Map(o => o.ToValidation<BaseError>($"MultiCollection {request.MultiCollectionId} does not exist."));
    }
}