C# 具有列表对象的ASP.NET Core 3.0 MVC更新模型-添加对象

我有以下课程：

public class Invoice
{    
     [key]
     public Guid InvoiceID { get; set; }
     public string Name { get; set; }
     public List<Invoice_item> Invoice_items { get; set; }
     
     public Invoice()
     {
         InvoiceID = Guid.NewGuid();
         Invoice_items = new List<Invoice_item>();
     }
} 

它很好用。我可以编辑这个模型。 控制员：

Invoice invoice = await _context.Invoice.Include(i => i.Invoice_items).Where(x => x.InvoiceID == id).FirstOrDefaultAsync();

invoice.Name = "2020/122";
invoice.Invoice_items[0].Description = "Some name";
invoice.Invoice_items[0].Price = 1;
invoice.Invoice_items[0].qty = 1;

_context.Update(invoice);
await _context.SaveChangesAsync();

// WORK OK

Invoice invoice = await _context.Invoice.Include(i => i.Invoice_items).Where(x => x.InvoiceID == id).FirstOrDefaultAsync();

invoice.Name = "2020/122";
invoice.Invoice_items[0].Description = "Description 1";
invoice.Invoice_items[0].Price = 1;
invoice.Invoice_items[0].qty 1;

Invoice_item item = new Invoice_item()
{
  Description = "Description 2",
  Price = 2,
  qty = 2
};

invoice.Invoice_items.Add(item);   // PROBLEM
                       
_context.Update(invoice);
await _context.SaveChangesAsync();

但问题是，当我想在列表中添加一个项目时： 控制员：

Invoice invoice = await _context.Invoice.Include(i => i.Invoice_items).Where(x => x.InvoiceID == id).FirstOrDefaultAsync();

invoice.Name = "2020/122";
invoice.Invoice_items[0].Description = "Some name";
invoice.Invoice_items[0].Price = 1;
invoice.Invoice_items[0].qty = 1;

_context.Update(invoice);
await _context.SaveChangesAsync();

// WORK OK

Invoice invoice = await _context.Invoice.Include(i => i.Invoice_items).Where(x => x.InvoiceID == id).FirstOrDefaultAsync();

invoice.Name = "2020/122";
invoice.Invoice_items[0].Description = "Description 1";
invoice.Invoice_items[0].Price = 1;
invoice.Invoice_items[0].qty 1;

Invoice_item item = new Invoice_item()
{
  Description = "Description 2",
  Price = 2,
  qty = 2
};

invoice.Invoice_items.Add(item);   // PROBLEM
                       
_context.Update(invoice);
await _context.SaveChangesAsync();

编辑“发票”记录时，可以编辑记录的所有元素以及附加到其上的“发票项目”列表的元素。当我想将一个项目添加到“发票”记录所附的“发票项目”列表时，就会出现问题

---

请提供帮助。

您只需在您的

项目中添加
发票\u itemID
，如下图所示更改代码

Invoice_item item = new Invoice_item()
        {
            //add this line.
            Invoice_itemID = new Guid(),
            Description = "Description 2",
            Price = 2,
            qty = 2
        };

你的错误是什么？您可以提供有关异常的详细信息吗？DbUpdateConcurrencyException:数据库操作预期会影响1行，但实际影响0行。此问题与
ChangeTracker
有关，您可以在链接上阅读您的
Invoice\u项目
实体是否设置了主键？是。Guid发票\u itemID是密钥