8.自增主键 插入指定主键的数据

Posted 2022-10-11 nocanstillbb

假设你有一个表Authors ,主键是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",
    
;

你想保存这个图,但是你指定了主键的值是1001,这里你不能直接savechanges,你应该首先打开IDENTITY_INSERT,保存后再删除

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");

但是这时保存的数据的 id不是1001,而会是数据库identity生成的序号

解决的方法是派生一个 datacontext的子类重写OnModelCreating

public class TempBookStore : BookStore

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    
        modelBuilder.Entity<Author>()
          .Property(a => a.AuthorId)
          .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
        base.OnModelCreating(modelBuilder);
    

然后在事务中savechangs

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();