INSTEAD OF INSERT 设置的主键在实体框架中抛出错误（ASP.NET 框架 c#）

Question

我刚开始使用 .NET 并一直在尝试对表执行 CRUD 操作。该表上有一个触发器，用于设置主键。现在，读取、更新和删除操作可以顺利进行。我的问题在于创建操作。

这是触发器

create or alter trigger dbo.CreateEmpID on dbo.Employee instead of insert
as
begin

declare @NextId varchar(20)
declare @EmpName varchar(50)
declare @cur cursor
set @cur = cursor for select EmpName from inserted
open @cur
fetch next from @cur into @EmpName
while @@FETCH_STATUS = 0
begin
    select @NextId = 'EMP' + convert(varchar(20), isNull(max(convert(int, substring(EmpID, 4, len(EmpID)-3))),0)+1) from Employee
    insert into Employee(EmpID, EmpName) values (@NextId, @EmpName)
    fetch next from @cur into @EmpName
end
close @cur
deallocate @cur

end

这是创建新员工的代码部分

//POST: Create
    [HttpPost]
    public ActionResult Create(Employee Emp)
    {
        DB.Employees.Add(Emp);
        DB.SaveChanges();
        return RedirectToAction("Index");
    }

这是我不断收到的错误

System.Data.Entity.Validation.DbEntityValidationException: 'Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.'

我还对另一件事感到困惑。在同一个表上还有另一个触发器在删除后工作，它将删除的员工复制到另一个表。那么是只有 INSTEAD OF 触发器有问题还是代码有问题。

感谢任何帮助。

编辑：

我将表格更改为使用第一个答案中提到的序列，但它仍然给我错误。这也是详细的错误

System.Data.Entity.Validation.DbEntityValidationException
  HResult=0x80131920
  Message=Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.
  Source=EntityFramework
  StackTrace:
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at Test.Controllers.HomeController.Index() in E:\vs\projects\Test\Test\Controllers\HomeController.cs:line 18
   at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
   at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c.<BeginInvokeSynchronousActionMethod>b__9_0(IAsyncResult asyncResult, ActionInvocation innerInvokeState)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`2.CallEndDelegate(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase`1.End()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_0.<InvokeActionMethodFilterAsynchronouslyRecursive>b__0()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_2.<InvokeActionMethodFilterAsynchronouslyRecursive>b__2()

Answer 1

这里可能会出现很多问题，但不值得进行故障排除，因为您永远不应该通过从目标表中查询 max(id)+1 来生成密钥。它无法扩展并且容易产生死锁。

如果你想要一个像EMP1234 这样的密钥，你可以用一个SEQUENCE 和一个DEFAULT 来生成它，参见例如和How to generate unique incremental employee code(pattern: E0001, E0002, E0003, ... ) in the INSERT stored procedure in SQL Server?

但通常您只需使用 SEQUENCE 或 IDENTITY COLUMN 并继续前进。