EF Core无跟踪查询遇循环包含错误，如何实现动态计算字段？

问题场景 #

我尝试通过EF Core的无跟踪查询获取Invoice实体及关联数据，查询代码如下：

await _invoiceReadSet.AsNoTracking()
                        .Include(i => i.Currency)
                        .Include(i => i.Customer)
                        .Include(i => i.Salesman)
                        .Include(i => i.InvoiceItems).ThenInclude(ii => ii.Item)
                        .Include(i => i.InvoiceItems).ThenInclude(ii => ii.Invoice)
                        .SingleOrDefaultAsync(c => c.Guid == guid, cancellationToken);

这么做是为了在InvoiceItems的Dto中动态计算Price和Total字段，避免持久化这两个值，Dto代码如下：

public Guid InvoiceGuid { get; set; }
public InvoiceDto Invoice { get; set; }
public Guid ItemGuid { get; set; }
public ItemDto Item { get; set; }

public decimal Price
    => Invoice.Customer.PriceChoice == PriceChoice.Retail ?
            Item.RetailPrice : Item.WholesalePrice;
public int Quantity { get; set; }
public decimal Discount { get; set; }
public decimal Total => Price * Quantity * Discount

执行时出现错误：

The Include path 'InvoiceItems->Invoice' results in a cycle. Cycles are not allowed in no-tracking queries; either use a tracking query or remove the cycle.

问题原因 #

你添加的.Include(i => i.InvoiceItems).ThenInclude(ii => ii.Invoice)属于冗余配置：EF Core在加载Invoice的InvoiceItems集合时，会自动将每个InvoiceItem的Invoice反向导航属性指向父Invoice实体，手动Include这个反向导航会形成Invoice -> InvoiceItems -> Invoice的循环引用，而无跟踪查询明确禁止这种循环Include配置。

解决方案 #

方案一：移除循环Include（优先推荐） #

直接删除.Include(i => i.InvoiceItems).ThenInclude(ii => ii.Invoice)这一行，修改后的查询代码如下：

await _invoiceReadSet.AsNoTracking()
    .Include(i => i.Currency)
    .Include(i => i.Customer)
    .Include(i => i.Salesman)
    .Include(i => i.InvoiceItems).ThenInclude(ii => ii.Item)
    .SingleOrDefaultAsync(c => c.Guid == guid, cancellationToken);

修改后，每个InvoiceItem的Invoice导航属性依然会被EF Core自动赋值，完全不影响你在Dto中通过Invoice.Customer.PriceChoice动态计算Price字段。

方案二：改用跟踪查询（不推荐，仅作备选） #

如果一定要保留这个循环Include（无实际必要），可以移除AsNoTracking()改用跟踪查询：

await _invoiceReadSet
    .Include(i => i.Currency)
    .Include(i => i.Customer)
    .Include(i => i.Salesman)
    .Include(i => i.InvoiceItems).ThenInclude(ii => ii.Item)
    .Include(i => i.InvoiceItems).ThenInclude(ii => ii.Invoice)
    .SingleOrDefaultAsync(c => c.Guid == guid, cancellationToken);

但跟踪查询会让实体进入变更追踪状态，对于仅用于映射Dto的场景，无跟踪查询的性能更优，因此优先选择方案一。

额外优化建议 #

你的InvoiceItemDto中同时保留了InvoiceGuid和Invoice导航属性，存在冗余，可根据实际使用场景保留其中一个即可；动态计算的Price和Total字段写法没问题，若后续需扩展逻辑，可考虑封装为私有方法或使用计算属性的完整写法（当前的表达式体写法已经足够简洁）。

内容的提问来源于stack exchange，提问作者Mohamad Al Jawad