How to set a property to be "Identity" or auto-incremented column with Entity Framework Core?

Question

In a new WPF project that I am writing using c#, I want to attempt on using Entity Framework Core to interact with my SQL Server database.

Every time I try to add model to my context, I get the following error

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

I am using a Repository and UnitOfWork which wraps the Entity Framework Core methods to perform the work needed.

But at its simplest, I am executing the following code

var order = new Order();
order.Title = "some";
....
Context.Orders.Add(order);
Context.SaveChanges();

Here is my model

public class Order
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Int64 Id { get; set; }

    public string Status { get; set; }
    public int? CustomerId { get; set; }
    public DateTime? Birthdate { get; set; }
    public int UtcOffset { get; set; }\
    public DateTime CreatedAt { get; set; }
    public DateTime? UpdatedAt { get; set; }
    public int? UpdatedBy { get; set; }

    [ForeignKey(nameof(Creator))]
    public int CreatedBy { get; set; }

    public Order()
    {
        CreatedAt = DateTime.UtcNow;
    }

    public virtual User Creator { get; set; }
    public virtual Customer Customer { get; set; }
}

What could be causing this problem?

Updated

Here is how my table is created

CREATE TABLE [dbo].[Orders](
    [Id] [bigint] IDENTITY(1,1) NOT NULL,
    [Status] [varchar](50) NOT NULL,
    [CustomerId] [int] NULL,
    [Birthdate] [datetime] NULL,
    [CreatedBy] [int] NOT NULL,
    [CreatedAt] [datetime] NOT NULL,
    [UpdatedBy] [int] NULL,
    [UpdatedAt] [datetime] NULL,
    [UtcOffset] [int] NOT NULL,
 CONSTRAINT [PK_Orders] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

Here is the method that creates the Order model

public Order Create(int? customerId, DateTime? birthdate)
{
    var order = new Order();
    order.CustomerId = customerId;
    order.Birthdate = birthdate;
    order.Status = OrderStatus.Sold.ToString();
    order.CreatedBy = Passport.Identity.Id;

    var updatedOrder = Orders.Add(order);
    Orders.Save();

    return updatedOrder;
}

Here is my repository implementation

public class EntityRepository<TEntity, TKeyType> : IRepository<TEntity, TKeyType>
    where TEntity : class
    where TKeyType : struct
{
    protected readonly DbContext Context;
    protected readonly DbSet<TEntity> DbSet;

    public EntityRepository(DbContext context)
    {
        Context = context;
        DbSet = context.Set<TEntity>();
    }

    public TEntity Get(TKeyType id)
    {
        return DbSet.Find(id);
    }

    public IEnumerable<TEntity> GetAll()
    {
        return DbSet.ToList();
    }

    public bool Any(Expression<Func<TEntity, bool>> predicate)
    {
        return DbSet.Any(predicate);
    }

    public IQueryable<TEntity> Find(Expression<Func<TEntity, bool>> predicate)
    {
        return DbSet.Where(predicate);
    }

    public TEntity SingleOrDefault(Expression<Func<TEntity, bool>> predicate)
    {
        return DbSet.SingleOrDefault(predicate);
    }

    public virtual TEntity Add(TEntity entity)
    {
        DbSet.Add(entity);

        return entity;
    }

    public virtual IEnumerable<TEntity> AddRange(IEnumerable<TEntity> entities)
    {
        DbSet.AddRange(entities);

        return entities;
    }

    public void Remove(TEntity entity)
    {
        DbSet.Remove(entity);
    }

    public void RemoveRange(IEnumerable<TEntity> entities)
    {
        DbSet.RemoveRange(entities);
    }

    public void Update(TEntity entity)
    {
        DbSet.Attach(entity);
        var record = Context.Entry(entity);
        record.State = EntityState.Modified;
    }

    public IQueryable<TEntity> Query()
    {
        return DbSet;
    }

    public void Save()
    {
        Context.SaveChanges();
    }
}

public class EntityRepository<TEntity> : EntityRepository<TEntity, int>
   where TEntity : class
{
    public EntityRepository(DbContext context)
        : base(context)
    {
    }
}

Additionally, this question is not a duplicate on Entity Framework error: Cannot insert explicit value for identity column in table because I am decorating my Id property with the [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]. Moreover, I am using database first approach, so I created my database manually using MSSMS

Answer 1

In my case I had to add entity.Property(e => e.TranId).ValueGeneratedOnAdd(); to my context file.

modelBuilder.Entity<PersonalTrades>(entity =>
{
     entity.Property(e => e.TranId).ValueGeneratedOnAdd();
}

I was not updating the identity field(TranId) from Automapper. Finally the above change worked for me which, as the name specifies, generates the value for the identity field while inserting the record.