如果项目存在，则创建或更新

Question

我有一个创建表单，如果存在特定Medicine，则其供应数量将更新或使用新条目添加，但是如果特定Medicine不存在，它将创建一批新数据。

我无法理解更新在 MVC 中的工作方式。

这是错误：

存储更新、插入或删除语句影响了意外的行数 (0(。自加载实体以来，实体可能已被修改或删除。

这是我的控制器：

public ActionResult Create([Bind(Include = "SupplyID,MedicineID,Expiration,NumberOfSupply")] Supply supply)
{
if (ModelState.IsValid)
{
bool supplyExsist = db.Supplies.Any(x => x.Expiration == supply.Expiration && x.MedicineID == supply.MedicineID);
if (supplyExsist)
{
var currentSupply = (from x in db.Supplies //get current supply
where x.MedicineID == supply.MedicineID
&& x.Expiration == supply.Expiration
select x.NumberOfSupply).First();
db.Entry(supply).State = EntityState.Modified;
supply.NumberOfSupply = currentSupply + supply.NumberOfSupply;
db.SaveChanges();
return RedirectToAction("Index");
}
else
{
db.Supplies.Add(supply);
db.SaveChanges();
return RedirectToAction("Index");
}
}
ViewBag.MedicineID = new SelectList(db.Medicines, "MedicineID", "MedicineName", supply.MedicineID);
return View(supply);
}

型：

public class Supply
{
[Key]
public int SupplyID { get; set; }
[ForeignKey("Medicine")]
public int MedicineID { get; set; }
public Medicine Medicine { get; set; }
[DataType(DataType.Date)]
public DateTime Expiration { get; set; }
[Display(Name = "Quantity")]
[Range(1, int.MaxValue, ErrorMessage = "The value must be greater than 0")]
public int NumberOfSupply { get; set; }
}

Answer 1

试试这个

db.Supplies.AddOrUpdate(h => h.medicineID,supply));

它将检查数据库中是否有具有相同药物 ID 的行，如果没有，它会添加一个新行，否则它会更新它

Answer 2

你应该用下面下面来改变你的if块：

if (supplyExsist)
{
var currentSupply = (from x in db.Supplies //get current supply
where x.MedicineID == supply.MedicineID
&& x.Expiration == supply.Expiration
select x.NumberOfSupply).First();
db.Supplies.Attach(supply);
db.Entry(supply).State = EntityState.Modified;
supply.NumberOfSupply = currentSupply + supply.NumberOfSupply;
db.SaveChanges();
return RedirectToAction("Index");
}