EF Core 插入标识问题

Question

I'm using EF Core 2.2.4 and I'm trying to insert datas through an asp.net MVC page.

Here's my repository insert command:

public int InsertFatorMarkup(int empId, GmPreFamFatMkp gmPreFamFatMkp, int usuId)
        {
            using (var transaction = _GFazContext.Database.BeginTransaction())
            {
                try
                {
                    var preFamFatId = EtapaInsertFator(empId, gmPreFamFatMkp, usuId);
                    transaction.Commit();
                    return preFamFatId;
                }
                catch (Exception ex)
                {
                    transaction.Rollback();
                    throw ex;
                }
            }
        }

        //Fernando Milanez 28/11/2019
        private int EtapaInsertFator(int empId, GmPreFamFatMkp gmPreFamFatMkp, int usuId)
        {
            gmPreFamFatMkp = RecargaDeDependenciasFator(empId, gmPreFamFatMkp);

            gmPreFamFatMkp.PreFamFatId = NextFatorMkpId(gmPreFamFatMkp.PreId, empId);
            gmPreFamFatMkp.RegrasNegocio(usuId);

            _GFazContext.GmPreFamFatMkp.Add(gmPreFamFatMkp);
            _GFazContext.SaveChanges();
            return gmPreFamFatMkp.PreFamFatId;
        }

        //Fernando Milanez 28/11/2019
        private GmPreFamFatMkp RecargaDeDependenciasFator(int empId, GmPreFamFatMkp gmPreFamFatMkp)
        {
            gmPreFamFatMkp.GmPreTab = GetById(empId, gmPreFamFatMkp.PreId);
            //gmPreFamFatMkp.GmPreTab = _GFazContext.GmPreTab
            //    .FirstOrDefault(r => r.EmpId == empId && r.PreId == gmPreFamFatMkp.PreId);

            return gmPreFamFatMkp;
        }

        //Fernando Milanez 28/11/2019
        private short NextFatorMkpId(int preId, int empId)
        {
            var max = _GFazContext.GmPreFamFatMkp
                .Where(r => r.PreId == preId)
                .Select(r => (int)r.PreFamFatId)
                .DefaultIfEmpty(0)
                .Max();

            return Convert.ToInt16(max + 1);
        }

Here's my controller Get and Post methods:

 [HttpGet]
        public IActionResult FamiliaMarkupInsert(int preId)
        {
            ViewBag.returnUrl = Request.Headers["Referer"].ToString();

            var model = new PreFamFatMkpModel();
            model.Form = new GmPreFamFatMkp() { PreId = preId };
            model.Form.GmPreTab = _gmPreTabRepositorio.GetById(_empId, preId, false);
            model.FamiliaModel = new FamiliaModel();
            GetDataCombo(ref model);

            return View(model);
        }

        //Fernando Milanez 29/11/2019
        [HttpPost]
        public IActionResult FamiliaMarkupInsert(PreFamFatMkpModel model)
        {
            ViewBag.returnUrl = Request.Headers["Referer"].ToString();
            if (ModelState.IsValid)
            {
                try
                {
                    int newPreFamFatId = _gmPreTabRepositorio.InsertFatorMarkup(_empId, model.Form, _usuId);
                    return RedirectToAction("TabelaPrecoTabs", new { id = model.Form.PreId, tabName= "Markup Por Família" });
                }
                catch (Exception ex)
                {
                    ModelState.AddModelError("", ex.Message);
                    if (ex.InnerException != null) ModelState.AddModelError("", ex.InnerException.Message);
                }
            }
            GetDataCombo(ref model);
            model.Form.GmPreTab = _gmPreTabRepositorio.GetById(_empId, model.Form.PreId);
            return View(model);
        }

Here's my configuration class:

public class GmPreFamFatMkpConfigurations : IEntityTypeConfiguration<GmPreFamFatMkp>
    {
        public void Configure(EntityTypeBuilder<GmPreFamFatMkp> builder)
        {
            builder.HasKey(r => new { r.PreFamFatId });
            builder.Property(r => r.PreFamFatId).UseSqlServerIdentityColumn();

            //Monta Relacionamento 1-N - Colocar somente as dependencias, nesse caso depende da tabela de preço e do produto

            builder.HasOne(prepro => prepro.GmPreTab).WithMany(pretab => pretab.GmPreFamFatMkps).HasForeignKey(prepro => prepro.PreId);

            builder.HasOne(prefamfatmkp => prefamfatmkp.GmPreTab).WithMany(famtab => famtab.GmPreFamFatMkps).HasForeignKey(prefamfatmkp => prefamfatmkp.PreId);


        }
    }

And finally, heres my error:

Unable to enter an explicit value for the identity column in table 'GmPreFamFatMkp' when IDENTITY_INSERT is set to OFF.

Answer 1

The error is pretty self explanatory. You've provided a value for the column 'GmPreFamFatMkp' and it is an Identity column (guessing auto-increment) and "Identity_Insert" is off. You probably want to leave it that way. You can't provide a value for this column. Give it null or zero value and let EF and the database figure out the correct value.