實體框架錯誤：字段“ForeignKey”是必需的EF

Question

我有一個實體設置如下

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; }
}

稍后在我的項目中，我使用此實體如下

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

db.SaveChanges();

拋出DbEntityValidationException“字段”RelationObj“是必需的”

我不想在加載這些記錄時包含RelationObj，這會影響性能。 為什么EF打擾檢查外來關系對象？ 我該如何解決這個問題？

Answer 1

首先創建數據庫，在腳本之上更改數據庫以匹配您的數據庫

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

然后創建下一個表，再次更改db（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

在每個表中添加幾行數據。

從您的數據庫添加新項ADO.NET實體數據模型並添加兩個表。 將edmx命名為ExampleModel。 從Example.Context.cs文件中獲取（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();
}

這是生成的示例：

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; }
    }
}

在這里id生成的Relation：

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; }
    }
}