c# - Entity Framework 错误 : The field "ForeignKey" is required EF

Question

我有一个实体设置如下

public class ExampleObject
{
    [Key]
    public int ID { get; set; }
    public int RelationID { get; set; }
    public string SomeValue { get; set; }

    [ForeignKey("RelationID")]
    public virtual RelationObj RelationObj { get; set; }
}

稍后在我的项目中我按如下方式使用这个实体

foreach (var rec in allRecs)
{
    db.ExampleObject.Attach(rec);
    rec.SomeValue = "TEST"
}

db.SaveChanges();

这会抛出 DbEntityValidationException “需要字段“RelationObj””

我不想在加载这些记录时包含 RelationObj，这会影响性能。 EF为什么要费心检查对外关系对象呢？我该如何解决这个问题？

Answer 1

首先创建数据库，在脚本之上更改数据库以匹配您的数据库

USE [Breaz]
GO

/****** Object:  Table [dbo].[Relation]    Script Date: 6/29/2016 4:35:32 PM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[Relation](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [RelatedSomeValue] [varchar](10) NULL,
 CONSTRAINT [PK_Relation] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

然后创建下一个表，再次更改数据库 (Breaz):

USE [Breaz]
GO

/****** Object:  Table [dbo].[Example]    Script Date: 6/29/2016 4:34:15 PM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[Example](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [RelationID] [int] NOT NULL,
    [SomeValue] [varchar](10) NULL,
 CONSTRAINT [PK_Example] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

ALTER TABLE [dbo].[Example]  WITH CHECK ADD  CONSTRAINT [FK_Example_Relation] FOREIGN KEY([RelationID])
REFERENCES [dbo].[Relation] ([ID])
GO

ALTER TABLE [dbo].[Example] CHECK CONSTRAINT [FK_Example_Relation]
GO

在每个表中添加几行数据。

从您的数据库添加新项目 ADO.NET 实体数据模型并添加两个表。命名 edmx ExampleModel。从 Example.Context.cs 文件中获取 (BreazEntities7) 上下文(您的上下文)。

 public class HomeController : Controller
{
    public ActionResult YIndex()
    {
        using (BreazEntities7 db = new BreazEntities7())
        {
            var allRecs = db.Examples;
            foreach (var rec in allRecs)
            {
                rec.SomeValue = "TEST";
            }
            db.SaveChanges();
        }
        return View();
}

这是生成的示例:

namespace Testy2.Models
{
    using System;
    using System.Collections.Generic;

    public partial class Example
    {
        public int ID { get; set; }
        public int RelationID { get; set; }
        public string SomeValue { get; set; }

        public virtual Relation Relation { get; set; }
    }
}

此处标识生成的关系:

namespace Testy2.Models
{
    using System;
    using System.Collections.Generic;

    public partial class Relation
    {
        public Relation()
        {
            this.Examples = new HashSet<Example>();
        }

        public int ID { get; set; }
        public string RelatedSomeValue { get; set; }

        public virtual ICollection<Example> Examples { get; set; }
    }
}