8. increment primary key insert designated primary data key

Suppose you have a table Authors, the primary key is AuthorId

Author author = new Author()
{
    AuthorId = 1001,
    Name = "Johny",
    Books = new List<Book>
    {
        new Book() { Title = "Learn VB.NET"},
        new Book() { Title = "C# Fundamentals for Absolute Beginners"},
    }
};

You want to save the map, but you specify a primary key value is 1001, where you can not directly savechanges, you should first open the IDENTITY_INSERT, save and then delete

using (var context = new BookStore())
{
    Author author = new Author()
    {
        AuthorId = 1001,
        Name = "Johny",
        Books = new List<Book>
        {
            new Book() { Title = "Learn VB.NET"},
            new Book() { Title = "C# Fundamentals for Absolute Beginners"},
        }
    };
    context.Authors.Add(author);
    
    context.Database.ExecuteSqlCommand(@"SET IDENTITY_INSERT [dbo].[Authors] ON");
    context.SaveChanges();
    context.Database.ExecuteSqlCommand(@"SET IDENTITY_INSERT [dbo].[Authors] OFF");
}

But then the saved data id is not 1001, but will generate a database of identity numbers

The solution is to subclass a datacontext rewrite OnModelCreating

public class TempBookStore : BookStore
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Author>()
          .Property(a => a.AuthorId)
          .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
        base.OnModelCreating(modelBuilder);
    }
}

Then savechangs in a transaction

using (var context = new TempBookStore())
{
    using (var transaction = context.Database.BeginTransaction())
    {
        Author author = new Author()
        {
            AuthorId = 1001,
            Name = "Johny",
            Books = new List<Book>
            {
                new Book() { Title = "Learn VB.NET"},
                new Book() { Title = "C# Fundamentals for Absolute Beginners"},
            }
        };
        context.Authors.Add(author);

        context.Database.ExecuteSqlCommand(@"SET IDENTITY_INSERT [dbo].[Authors] ON");
        context.SaveChanges();
        context.Database.ExecuteSqlCommand(@"SET IDENTITY_INSERT [dbo].[Authors] OFF");
            
        transaction.Commit();
    }
}