c# - Entity Framework 代码优先级联删除一对多

Question

我正在尝试创建一个小型演示解决方案来试验 EF CF 级联删除。

使用我编写的代码，在尝试添加一个有 2 辆车的人时出现以下错误。

目标是添加一个拥有 2 辆车的人。然后删除人，同时删除关联的汽车。

System.InvalidCastException: Unable to cast object of type 'System.Collections.Generic.List`1[EF_Cascading_Delete_Experiment.Car]' to type 'EF_Cascading_Delete_Experiment.Car'.

我正在尝试构建一个简单的示例，其中有一个带有汽车列表的人

这是我的个人和汽车类别:

public class Person
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    public List<Car> Cars { get; set; }
}
public class Car
{
    [Key]
    public int id { get; set; }
    public string CarName { get; set; }
}

这是我试图为一个有 2 辆车的人做广告的简单代码:

public static void CarTest()
    {
        using (Model1 db = new Model1())
        {
            Person personToAdd = new Person();
            personToAdd.Name = "trev";
            personToAdd.Cars = new List<Car>();

            Car car1 = new Car
            {
                CarName = "Vectra"
            };

            Car car2 = new Car
            {
                CarName = "Focus"
            };

            personToAdd.Cars.Add(car1);
            personToAdd.Cars.Add(car2);

            db.Person.Add(personToAdd);

            db.SaveChanges();
        }
    }

错误发生在行

db.Person.Add(personToAdd);

这是我的 DbContext:

public class Model1 : DbContext
{
    // Your context has been configured to use a 'Model1' connection string from your application's 
    // configuration file (App.config or Web.config). By default, this connection string targets the 
    // 'EF_Cascading_Delete_Experiment.Model1' database on your LocalDb instance. 
    // 
    // If you wish to target a different database and/or database provider, modify the 'Model1' 
    // connection string in the application configuration file.
    public Model1()
        : base("name=Model1")
    {
    }

    // Add a DbSet for each entity type that you want to include in your model. For more information 
    // on configuring and using a Code First model, see http://go.microsoft.com/fwlink/?LinkId=390109.

    public virtual DbSet<Person> Person { get; set; }
    public virtual DbSet<Car> Car { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Person>()
            .HasOptional(a => a.Cars)
            .WithOptionalDependent()
            .WillCascadeOnDelete(true);
    }
}

EF 生成的迁移代码如下所示:

public partial class addedbackeverythingincludingcascadingdelete : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.Cars",
            c => new
                {
                    id = c.Int(nullable: false, identity: true),
                    CarName = c.String(),
                })
            .PrimaryKey(t => t.id);

        CreateTable(
            "dbo.People",
            c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    Name = c.String(),
                    Cars_id = c.Int(),
                })
            .PrimaryKey(t => t.Id)
            .ForeignKey("dbo.Cars", t => t.Cars_id, cascadeDelete: true)
            .Index(t => t.Cars_id);

    }

    public override void Down()
    {
        DropForeignKey("dbo.People", "Cars_id", "dbo.Cars");
        DropIndex("dbo.People", new[] { "Cars_id" });
        DropTable("dbo.People");
        DropTable("dbo.Cars");
    }
}

在我看来，迁移代码似乎不正确？这将根据我的 Person & Car 类生成。但我不知道为什么？

当我查看数据库中的表时，它们看起来是错误的。

肯定在 Car 表中应该有一个 PersonId？ Person 表中没有 CarId？

解决方案:

非常感谢 Ivan，这是我的解决方案。我已将其放在这里，以便我可以将他的问题标记为答案。

我的类现在看起来像这样:

public class Person
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual List<Car> Cars { get; set; }
}
public class Car
{
    [Key]
    public int id { get; set; }
    public string CarName { get; set; }
}

测试时，尽管 Ivan 说我不需要它，但我发现级联删除将不起作用，除非我保留此代码:

modelBuilder.Entity<Person>()
            .HasMany(a => a.Cars)
            .WithOptional() // or `WithRequired() in case Car requires Person
            .WillCascadeOnDelete(true);

Answer 1

流畅的关系配置

modelBuilder.Entity<Person>()
    .HasOptional(a => a.Cars)
    .WithOptionalDependent()
    .WillCascadeOnDelete(true);

错了。 HasOptional, HasRequired, WithOptionalDependent, WithOptionalPrincipal 等用于一对一 关系，而你有一对多。

正确的配置如下:

modelBuilder.Entity<Person>()
    .HasMany(a => a.Cars)
    .WithOptional() // or `WithRequired() in case Car requires Person
    .WillCascadeOnDelete(true);

现在迁移应该是这样的:

CreateTable(
    "dbo.People",
    c => new
        {
            Id = c.Int(nullable: false, identity: true),
            Name = c.String(),
        })
    .PrimaryKey(t => t.Id);

CreateTable(
    "dbo.Cars",
    c => new
        {
            id = c.Int(nullable: false, identity: true),
            CarName = c.String(),
            Person_Id = c.Int(),
        })
    .PrimaryKey(t => t.id)
    .ForeignKey("dbo.People", t => t.Person_Id, cascadeDelete: true)
    .Index(t => t.Person_Id);