ASP.net 检测到 6 个对象周期自动映射器嵌套列表

Question

我目前正在做一个个人项目，我想将UserTransaction映射到GetAllTransactionRes，并在命中API/transaction时从我的数据库中返回所有UserTransaction。每次使用API/transaction端点时，我都会收到此错误

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.

这是UserTransaction实体

public class UserTransaction
{
public int TransactionId { get; set; }
public DateTime Date { get; set; }
public virtual ICollection<OrderedProduct> OrderedProducts { get; set; }
}

这是Ordered Product实体

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; }
}

这是我的映射器。GetAllTransactionRes和AllOrderedProductDTO是UserTransaction和OrderedProduct实体的精确副本。

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

因为我正在使用MediatR。这是我的GetAllTransactionQuery处理程序

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;
}

在使用自动映射器之前，我使用了efcore中的.include方法，这给了我与搜索答案相同的错误，并且有人在 StackOverflow 问题中评论说我不应该直接在我的 API 中返回数据库实体。这是发布上述评论的问题

我做错了什么？谢谢

Answer 1

问题是您的AllOrderedProductDTO和GetAllTransactionRes数据传输对象具有循环引用 - 事务包含包含包含产品的事务的产品...

以下是我建议打破循环的DTO类：

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; }
}

Answer 2

我有一个类似的问题。我通过添加装饰来解决这个问题。

参考文档：https：//learn.microsoft.com/en-us/ef/core/querying/related-data/serialization

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; }
[JsonIgnore]
public virtual UserTransaction UserTransaction { get; set; }
}