Hands-On RESTful Web Services with ASP.NET Core 3

Existence check

Let's start by implementing the action filter that performs an existence check on the requested data. The filter will be used by the action methods that get or edit a single item. As seen in Chapter 7, Filter Pipeline, we are going to implement the following filter:

using System;using System.Threading.Tasks;using Catalog.Domain.Requests.Item;using Catalog.Domain.Services;using Microsoft.AspNetCore.Mvc;using Microsoft.AspNetCore.Mvc.Filters;namespace Catalog.API.Filters{    public class ItemExistsAttribute : TypeFilterAttribute    {        public ItemExistsAttribute() : base(typeof            (ItemExistsFilterImpl))        {        }        public class ItemExistsFilterImpl : IAsyncActionFilter        {            private readonly IItemService _itemService;            public ItemExistsFilterImpl ...