使用实体框架手动输入密钥 [英] Entering keys manually with Entity Framework

问题描述

我首先尝试将 Entity Framework 代码用于一个简单的数据库项目，但遇到了一个我根本无法弄清楚的问题.

I'm trying to use Entity Framework code first for a simple database project and I run into a problem I simply cannot figure out.

我注意到 EF 正在为我的表设置 ID，每次自动增加 1，完全忽略我为该字段手动输入的值.经过一番搜索，我了解到禁用此行为的正确方法是:

I noticed EF was setting the ID for my tables automatically increasing by 1 each time, completely ignoring the value I entered manually for that field. After some searching it is my understanding that the right way to disable this behavior is doing:

modelBuilder.Entity<Event>().Property(e => e.EventID).HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

但是现在我刚刚收到此错误，我不知道为什么:

However now I'm just getting this error and I have no idea why:

未处理的异常:System.Data.Entity.Infrastructure.DbUpdateException:错误更新条目时发生.请参阅内部异常细节.---

Unhandled Exception: System.Data.Entity.Infrastructure.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---

System.Data.UpdateException:更新条目时出错.有关详细信息，请参阅内部异常.--->System.Data.SqlClient.SqlException:无法插入显式值IDENTITY_INSERT 设置为 OFF 时表 'Events' 中的标识列.

System.Data.UpdateException: An error occurred while updating the entries. See the inner exception for details. ---> System.Data.SqlClient.SqlException: Cannot insert explicit value for identity column in table 'Events' when IDENTITY_INSERT is set to OFF.

如果有帮助，这里是有问题的 POCO 类:

If it's helpful, here is the POCO class in question:

public class Event
{
    [Key, Required]
    public int EventID { get; set; }

    public string EventType { get; set; } //TODO: Event Type Table later on
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }

    public virtual ICollection<Match> Matches { get; set; }
    public virtual ICollection<EventParticipation> EventParticipation { get; set; }
}

提前致谢.

推荐答案

默认情况下，Entity Framework 假定一个整数主键是数据库生成的(相当于添加属性 HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity) 或在 Fluent API 中调用 Property(e => e.EventID).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);.

By default Entity Framework assumes that an integer primary key is database generated (equivalent to adding the attribute HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity) or calling Property(e => e.EventID).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity); in the Fluent API.

如果您查看创建表的迁移，您应该看到:

If you look at the migration that creates the table you should see this:

   CreateTable(
                "dbo.Events",
                c => new
                    {
                        EventID = c.Int(nullable: false, identity: true),
                        //etc
                    })
                .PrimaryKey(t => t.EventID );

然后您使用 Fluent API 将模型更改为 DatabaseGenerated.None.EF 将其放入迁移中:

Then you changed the model using the Fluent API to DatabaseGenerated.None. EF puts this in the migration:

AlterColumn("dbo.Events", "EventID", c => c.Int(nullable: false, identity: false))

生成的sql是这样的:

And the sql generated is this:

ALTER TABLE [dbo].[Events] ALTER COLUMN [EventID] [int] NOT NULL

实际上确实是深蹲.从列中删除 IDENTITY 不是琐碎的.您需要删除并重新创建表或创建一个新列，然后您必须复制数据并修复外键.因此，EF 不为您做这件事也就不足为奇了.

Which actually does diddly squat. Dropping the IDENTITY from a column is not trivial. You need to drop and recreate the table or create a new column, then you have to copy the data and fix up foreign keys. So it's not surprising that EF isn't doing that for you.

你需要想出如何最好地为自己做这件事.既然您已经指定了 DatabaseGeneratedOption.None，您可以将迁移回滚到 0 并从头开始重新构建，或者您可以手动更改迁移以删除并重新创建表.

You need to work out how best to do it for yourself. You could roll back your migrations to 0 and re-scaffold from scratch now that you have specified DatabaseGeneratedOption.None, or you could change the migration manually to drop and recreate the table.

或者您可以删除并重新创建该列:

Or you could drop and recreate the column:

DropColumn("Customer", "CustomerId"); 
AddColumn("Customer", "CustomerId", c => c.Long(nullable: false, identity: false));

编辑或者你可以开启身份识别/Off 使用自定义迁移操作

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