檢測到ASP.net6物件回圈自動映射器嵌套串列

我目前正在從事一個個人專案，我想在命中時將其映射UserTransaction到GetAllTransactionRes并UserTransaction從我的資料庫中回傳所有內容API/transaction。每次我使用API/transaction端點時，我都會收到此錯誤

System.Collections.Generic.List`1[ProjectName.Modules.Transaction.Core.DTO.GetAllTransactionRes]
fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
      An unhandled exception has occurred while executing the request.
      System.Text.Json.JsonException: A possible object cycle was detected. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 32. Consider using ReferenceHandler.Preserve on JsonSerializerOptions to support cycles. Path: $.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.OrderedProducts.UserTransaction.TransactionId.

這是UserTransaction物體

    public class UserTransaction
    {
        public int TransactionId { get; set; }
        public DateTime Date { get; set; }

        public virtual ICollection<OrderedProduct> OrderedProducts { get; set; }
    }

這是Ordered Product物體

    public class OrderedProduct
    {
        public int Id { get; set; }
        public string Product { get; set; }
        public int ProductId { get; set; }
        public int Quantity { get; set; }
        public bool Returned { get; set; }

        public int TransactionId { get; set; }
        public virtual UserTransaction UserTransaction { get; set; }
    }

這是我的映射器。GetAllTransactionRes并且AllOrderedProductDTO是UserTransaction和OrderedProduct物體的精確副本。

CreateMap<UserTransaction, GetAllTransactionRes>().ForMember(s => s.OrderedProducts, c => c.MapFrom(m => m.OrderedProducts));
CreateMap<OrderedProduct, AllOrderedProductDTO>();

因為我使用的是 MediatR。這是我的處理程式GetAllTransactionQuery

        public async Task<ICollection<GetAllTransactionRes>> Handle(GetAllTransactionQuery request, CancellationToken cancellationToken)
        {
            var Transactions = await _context.UserTransactions.Include(ut => ut.OrderedProducts).ToListAsync();
            var mapped = _mapper.Map<ICollection<UserTransaction>, ICollection<GetAllTransactionRes>>(Transactions);
            return mapped;
        }

在使用 automapper 之前，我使用的.include方法efcore給了我相同的錯誤，我搜索了答案，并且有人在 StackOverflow 問題中評論說我不應該直接在我的 API 中回傳資料庫物體。這是發布上述評論的問題

我究竟做錯了什么？謝謝

uj5u.com熱心網友回復：

問題是您AllOrderedProductDTO和您的GetAllTransactionRes資料傳輸物件具有回圈參考 - 交易包含產品，其中包含包含產品的交易......

以下是我建議打破回圈的 DTO 課程：

public class GetAllTransactionRes
{
    public int TransactionId { get; set; }
    public DateTime Date { get; set; }
    // be sure to use the products DTO here and not the entity because the entity has the loop
    public virtual ICollection<AllOrderedProductDTO> OrderedProducts { get; set; }
}

public class AllOrderedProductDTO
{
    public int Id { get; set; }
    public string Product { get; set; }
    public int ProductId { get; set; }
    public int Quantity { get; set; }
    public bool Returned { get; set; }

    public int TransactionId { get; set; }
    // do not include the transaction entity or DTO here so that we avoid the loop
    //public virtual UserTransaction UserTransaction { get; set; }
}

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