c# - MVC Seed不会将数据放入数据库中

我有两个表，它们之间有关系。

这是我的模型：

public  class Locations
{
  [Key]
  public int LocationID { get; set; }

  [Required(ErrorMessage = "This field is required!")]
  [MaxLength(50, ErrorMessage = "The name is too long. Max. 50 characters allowed!")]
  [Display(Name = "Location name:")]
  public string Name { get; set; }

  public int Position { get; set; }

  public virtual LocationType LocationType { get; set; }

}

和

public class LocationType
{
  [Key]
  public int LocationTypeID { get; set; }

  [Required(ErrorMessage = "This field is required!")]
  [MaxLength(25, ErrorMessage = "The name is too long. Max. 25 characters allowed!")]
  [Display(Name = "Location type:")]
  public string Name { get; set; }

  public int Position { get; set; }

  public int HasChoicesOrInput { get; set; }

  public virtual ICollection<Locations> Locations { get; set; }
}

在我的configuration.cs文件中，我具有以下种子：

context.LocationType.AddOrUpdate(a => a.LocationTypeID,
  new LocationType
  {
    Name = "AAAAA",
    HasChoicesOrInput = 1,
    Position = 1,
    Locations = { new Locations { Name = "1111111", Position = 1 },
                    new Locations { Name = "2222222", Position = 2 }
                }
  });

表定义：

CREATE TABLE [dbo].[Locations] (
[LocationID]                  INT           IDENTITY (1, 1) NOT NULL,
[Name]                        NVARCHAR (50) NOT NULL,
[Position]                    INT           NOT NULL,
[LocationType_LocationTypeID] INT           NULL,
CONSTRAINT [PK_dbo.Locations] PRIMARY KEY CLUSTERED ([LocationID] ASC),
CONSTRAINT [FK_dbo.Locations_dbo.LocationTypes_LocationType_LocationTypeID] FOREIGN KEY ([LocationType_LocationTypeID]) REFERENCES [dbo].[LocationTypes] ([LocationTypeID])
);

CREATE TABLE [dbo].[LocationTypes] (
[LocationTypeID]    INT           IDENTITY (1, 1) NOT NULL,
[Name]              NVARCHAR (25) NOT NULL,
[Position]          INT           NOT NULL,
[HasChoicesOrInput] INT           NOT NULL,
CONSTRAINT [PK_dbo.LocationTypes] PRIMARY KEY CLUSTERED ([LocationTypeID] ASC)
);

当我执行更新数据库时，会收到“对象引用未设置为对象的实例”。错误。

为什么？表存在于数据库中，关系也存在。
我在这里想念什么？

最佳答案

Locations初始化器

new LocationType
{
  Name = "AAAAA",
  HasChoicesOrInput = 1,
  Position = 1,
  Locations = { new Locations { Name = "1111111", Position = 1 },
                new Locations { Name = "2222222", Position = 2 }
            }
});

不创建Locations集合。它调用属性getter以获取现有的Locations集合，并对其调用Add。由于您从未为该属性分配任何内容，因此得到了NullReferenceException。

在C＃语言规范的7.6.10.2对象初始化程序部分中描述了此语法：


  在等号后指定集合初始化器的成员初始化器是嵌入式集合的初始化。代替为字段或属性分配新的集合，将初始化器中给定的元素添加到字段或属性引用的集合中。
  您应该创建一个新的集合实例（例如列表或数组），并将其分配给初始化程序中的Locations属性：

new LocationType
{
  Name = "AAAAA",
  HasChoicesOrInput = 1,
  Position = 1,
  Locations = new List<Locations>
  {
      new Locations { Name = "1111111", Position = 1 },
      new Locations { Name = "2222222", Position = 2 }
  }
});