当IDENTITY_INSERT设置为OFF时，无法为标识列插入显式值

Question

I'm attempting to set up a composite primary key with the second key being the year.

I've set both in the table creation and the constructor to auto generate the field but I still get this error:

Cannot insert explicit value for identity column in table Volunteer when IDENTITY_INSERT is set to OFF.

All three parts to the code and setup are below.

  [Table("Volunteer")]
    public class Volunteer
    {

        [Key][Column(Order = 0)]
        public int Id { get; set; }

        [DisplayName("First Name")]
        public string FirstName { get; set; }

        [DisplayName("Last Name")]
        public string LastName { get; set; }

        [DisplayName("Team Mentored")]
        public string TeamMentored { get; set; }


        [Key][Column(Order = 1)] [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public DateTime Year { get; set; }
        public string TableNumber { get; set; }
        public int OfficeId { get; set; }
        public string Image { get; set; }


    }

CREATE TABLE [dbo].[Volunteer](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [FirstName] [nvarchar](255) NULL,
    [LastName] [nvarchar](255) NULL,
    [TeamMentored] [nvarchar](255) NULL,
    [Year] [date] DEFAULT(getdate()) NOT NULL,
    [TableNumber] [nvarchar](50) NULL,
    [OfficeId] [int] NOT NULL,
    [Image] [nvarchar](max) NULL
 )


public ActionResult Create([Bind(Include = "FirstName,LastName,TeamMentored,TableNumber,OfficeId,Image")] Volunteer volunteer)
        {
            try
            {

                if (ModelState.IsValid)
                {
                    db.Volunteers.Add(volunteer);
                    db.SaveChanges();

                    ModelState.Clear();
                } 

                // TODO: Add insert logic here

                return RedirectToAction("Index");
            }
            catch
            {
                ModelState.AddModelError("", "DB Update Failed!"); 
            }

            return View();
        }

Answer 1

Try using the attribute [DatabaseGenerated(DatabaseGeneratedOption.Identity)] on "Id" property. If that doesn't do it, is it possible to post the code of assignment and save?

Answer 2

Your attribute [DatabaseGenerated(DatabaseGeneratedOption.Identity)] tells Entity Framework (and SQL Server) that the property will be auto-generated by the database using an auto-incrementing value. Therefore, you can not provide it a value.

If it will work at all, you will have to move it to the Id property. It would probably work, but I can't say for certain as I haven't worked with a composite Key before.

If you are still getting the error, then it is because the database has been created with the Year column set as int identity(1,1) . Either manually edit the database, or delete it and recreate it with a new migration.