如何告诉Entity Framework我的ID列是自动递增的(AspNet Core 2.0 + PostgreSQL)? [英] How to tell Entity Framework that my ID column is auto-incremented (AspNet Core 2.0 + PostgreSQL)?

问题描述

代码很简单. Tag.cs实体:

public partial class Tag
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
}

HomeController.cs类:

public async Task<IActionResult> Index()
{
   tagRepository.Insert(new Tag 
               { 
                   Name = "name", 
                   Description = "description" 
               });
   await UnitOfWork.SaveChangesAsync();  // calls dbContext.SaveChangesAsync()

   return View();
}

TagRepository.cs类:

    // Context it's a usual DBContext injected via Repository's constructor
    public virtual void Insert(TEntity item)
                => Context.Entry(item).State = EntityState.Added;

Tag表是通过运行以下命令创建的:

Tag table was created by running:

CREATE TABLE Tag (
    ID SERIAL PRIMARY KEY,
    Name text NOT NULL,
    Description text NULL
);

运行我的应用程序时出现错误:

When run my application I get an error:

fail: Microsoft.EntityFrameworkCore.Database.Command[20102]
      Failed executing DbCommand (28ms) [Parameters=[@p0='?', @p1='?', @p2='?'], CommandType='Text', CommandTimeout='30']
      INSERT INTO "tag" ("id", "description", "name")
      VALUES (@p0, @p1, @p2);
Npgsql.PostgresException (0x80004005): 23505: duplicate key value violates unique constraint "tag_pkey"
   at Npgsql.NpgsqlConnector.<DoReadMessage>d__157.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at System.Runtime.CompilerServices.ValueTaskAwaiter`1.GetResult()
   at Npgsql.NpgsqlConnector.<ReadMessage>d__156.MoveNext()

您可以看到Entity Framework尝试将id=0值发送到数据库，但是在我的数据库中已经有一条带有id=0的记录，这就是为什么它会引发duplicate key错误的原因.

As you can see Entity Framework tries to send id=0 value to the DB, but there is already a record with id=0 in my DB and that's why it throws duplicate key error.

到目前为止，我没有找到任何答案，我的问题是:如何摆脱这个错误，并告诉Entity Framework我的id列是自动递增的，不需要更新? >

I didn't find any answer so far and my question is: how can I get rid of this error and tell Entity Framework that my id column is auto-incremented and there is no need to update it?

推荐答案

您必须在此处使用"ValueGenerationOnAdd()" .由于您遇到的问题已在GitHub上进行了报告.请找到以下链接.

You have to use here "ValueGenerationOnAdd()". As the issue you are getting is already reported on GitHub. Please find the below link.

https://github.com/npgsql/Npgsql.EntityFrameworkCore .PostgreSQL/issues/73

https://github.com/npgsql/Npgsql.EntityFrameworkCore.PostgreSQL/issues/73

您可以从以下链接中找到有关生成值"模式的更多信息.

You can find more info regarding Generated Value pattern from following link.

添加时生成的值

public classs SampleContext:DBContext{
public DbSet<Tag> Tag { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder){
    modelBuilder.Entity<Tag>()
        .Property(p => p.ID)
        .ValueGeneratedOnAdd();
 }
public class Tag{
  public int Id { get; set; }
  public string Name { get; set; }
  public string Description{get;set;}
  }
}

来源:- https://www.learnentityframeworkcore.com/configuration/fluent -api/valuegenerationonadd-method

希望这会有所帮助

这篇关于如何告诉Entity Framework我的ID列是自动递增的(AspNet Core 2.0 + PostgreSQL)?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！