61 lines
2.3 KiB
C#
61 lines
2.3 KiB
C#
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using MediatR;
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using Microsoft.eShopOnContainers.Services.Ordering.Infrastructure.Repositories;
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Threading.Tasks;
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namespace Microsoft.eShopOnContainers.Services.Ordering.API.Application.Commands
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{
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/// <summary>
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/// Provides a base implementation for handling duplicate request and ensuring idempotent updates, in the cases where
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/// a requestid sent by client is used to detect duplicate requests.
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/// </summary>
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/// <typeparam name="T">Type of the command handler that performs the operation if request is not duplicated</typeparam>
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/// <typeparam name="R">Return value of the inner command handler</typeparam>
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public class IdentifierCommandHandler<T, R> : IAsyncRequestHandler<IdentifiedCommand<T, R>, R>
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where T : IAsyncRequest<R>
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{
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private readonly IMediator _mediator;
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private readonly IRequestManager _requestManager;
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public IdentifierCommandHandler(IMediator mediator, IRequestManager requestManager)
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{
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_mediator = mediator;
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_requestManager = requestManager;
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}
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/// <summary>
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/// Creates the result value to return if a previous request was found
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/// </summary>
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/// <returns></returns>
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protected virtual R CreateResultForDuplicateRequest()
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{
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return default(R);
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}
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/// <summary>
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/// This method handles the command. It just ensures that no other request exists with the same ID, and if this is the case
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/// just enqueues the original inner command.
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/// </summary>
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/// <param name="message">IdentifiedCommand which contains both original command & request ID</param>
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/// <returns>Return value of inner command or default value if request same ID was found</returns>
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public async Task<R> Handle(IdentifiedCommand<T, R> message)
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{
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var alreadyExists = await _requestManager.ExistAsync(message.Id);
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if (alreadyExists)
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{
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return CreateResultForDuplicateRequest();
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}
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else
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{
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await _requestManager.CreateRequestForCommandAsync<T>(message.Id);
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var result = await _mediator.SendAsync(message.Command);
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return result;
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}
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}
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}
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}
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