实体框架核心自动生成的 guid [英] Entity Framework Core Auto Generated guid

问题描述

有人可以指导我吗我想要一个表的 primeryKey 作为 guid 在插入时具有 db 生成的值.

Can some One guide me I want primeryKey of a table as guid having db generated value on insert.

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

但它给出了error

无法添加实体类型User"的种子实体，因为没有为所需的属性Id"提供值.

The seed entity for entity type 'User' cannot be added because there was no value provided for the required property 'Id'.

这是我的实际模型类和 DbContxt 类:

Here is my actual model classes and DbContxt class:

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

     [Required]
     [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
     public DateTime CreatedOn { get; set; } = DateTime.UtcNow;


     [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
     public DateTime? UpdatedOn { get; set; }

     [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
     public DateTime LastAccessed { get; set; }
 }

 public class User : BaseModel
 {
        [Required]
        [MinLength(3)]
        public string Name { get; set; }

        [Required]
        [MinLength(3)]
        [EmailAddress]
        public string Email { get; set; }

        [Required]
        [MinLength(6)]
        public string Password { get; set; }
  }

然后在 MyDbContext 中:

Then in the MyDbContext:

public class MyDbContext: DbContext
    {
        public MyDbContext(DbContextOptions<MyDbContext> options)
            : base(options)
        {
        }

        protected override void OnModelCreating(ModelBuilder mb)
        {
            base.OnModelCreating(mb);
            
            mb.Entity<User>().HasData(
                new User() { Email = "[e-mail]", Name = "Mubeen", Password = "123123" },
                new User() { Email = "[e-mail]", Name = "Tahir", Password = "321321" },
                new User() { Email = "[e-mail]", Name = "Cheema", Password = "123321" }
                );
        }

        public DbSet<User> User { get; set; }
    }

请帮忙！

推荐答案

您遇到的问题并非特定于自动生成的 Guid.对于任何自动生成的键值也会发生同样的情况，包括常用的自动增量(标识)列.

The problem you are experiencing is not specific for autogenerated Guids. The same happens for any autogenerated key values, including the commonly used auto increment (identity) columns.

这是由特定的数据播种 (HasData) 要求:

It's caused by a specific Data Seeding (HasData) requirement:

这种类型的种子数据由迁移管理，需要在不连接数据库的情况下生成更新数据库中已有数据的脚本.这施加了一些限制:

This type of seed data is managed by migrations and the script to update the data that's already in the database needs to be generated without connecting to the database. This imposes some restrictions:

• 即使通常由数据库生成，也需要指定主键值.它将用于检测迁移之间的数据更改.
• 如果主键以任何方式更改，则先前植入的数据将被删除.

注意第一项.因此，对于普通的 CRUD，您的 PK 将自动生成，当使用 HasData fluent API 时，您需要指定它，并且该值必须是恒定的(不改变)，所以你不能使用 Guid.NewGuid().所以你需要生成几个 Guids，获取它们的字符串表示并使用这样的东西:

Note the first bullet. So while for normal CRUD your PK will be auto generated, you are required to specify it when using HasData fluent API, and the value must be constant (not changing), so you can't use Guid.NewGuid(). So you need to generate several Guids, take their string representation and use something like this:

mb.Entity<User>().HasData(
    new User() { Id = new Guid("pre generated value 1"), ... },
    new User() { Id = new Guid("pre generated value 2"), ... },
    new User() { Id = new Guid("pre generated value 3"), ... }
    );

这篇关于实体框架核心自动生成的 guid的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！