ASP.NET MVC 错误 SqlException：当 IDENTITY_INSERT 设置为 OFF 时，无法在表“用户”中插入标识列的显式值

Question

I'm trying to make a login AUTH with C# .NET but I'm getting this error and can't solve it.

Here is my code.

User class

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int UserId { get; set; }
    public string Name { get; set; }
    public string Email { get; set; }
    public string Password { get; set; }

RegisterDTO

    public string Name { get; set; }
    public string Email { get; set; }
    public string Password { get; set; }
 

IUserRepository

public class UserRepository : IUserRepository
{
    private readonly ApiDbContext _context;

    public UserRepository(ApiDbContext context) 
    {
        _context = context;
    }

    public User Create(User user)
    {
        _context.Users.Add(user);
        user.UserId =_context.SaveChanges();
        return user;
    }
}

And the error I'm getting is when I start Swagger and trying to post username email and password:

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

Answer 1

In your database, your Users table is defined as

CREATE TABLE Users (
...
UserId int identity(1,1)
...
)

This means that your database wants to generate the UserId value for you, unless Identity_Insert=off is specified when a record in inserted. However, when you are calling Create(), the query that is being executed includes the UserId column.

You don't state in your question (or your tags) that your are using EntityFramework, but from your syntax, I am making that assumption. As such, you should specify this in your OnModelCreating method.

protected override void OnModelCreating(ModelBuilder modelBuilder) 
{
...
modelBuilder.Entity<Users>(Entity =>
  {
...
    Entity.Property(e=>e.UserId).ValueGeneratedOnAdd();
...
  }
...
}

Answer 2

You most likely generated the model before adding the [DatabaseGenerated(DatabaseGeneratedOption.Identity)] attribute. And its being cached in your *.edmx file.

I had such experience, and I was able to resolve by clearing out EF cache and *.edmx files, hence forcing the regeneration of my models.