c# - 在 Entity Framework 中存储自定义对象列表

Question

开始学习asp.net和DB操作。尝试实现一些简单的功能 - 两个模型，一个具有对另一个的引用列表。

这是我目前遇到的一个错误:

An exception occurred while initializing the database. See the InnerException for details.

Inner exception:
Unable to determine a valid ordering for dependent operations. Dependencies may exist due to foreign key constraints, model requirements, or store-generated values.

我的模型:

public class Killer
{
        public Killer(string name, string biography)
        {
            Name = name;
            Biography = biography;
            KillerId = Guid.NewGuid();
        }

        public Guid KillerId { get; set; }
        public string Name { get; set; }
        public string Biography { get; set; }

        public virtual Contract Contract { get; set; }
}

public class Contract
{
        public Contract(Status status, Killer target, string description, params Killer[] targets)
        {
            ContractId = Guid.NewGuid();
            this.status = status;
            Target = target;
            Description = description;

            Killers = new HashSet<Killer>();
            foreach (var t in targets) Killers.Add(t);

        }

        public Guid ContractId { get; set; }

        public enum Status { active, done, failed, rejected, abandoned }
        public Status status { get; set; }

        public Killer Target { get; set; }
        public string Description { get; set; }

        //[ForeignKey("ContractID")]
        public virtual ICollection<Killer> Killers { get; set; }
}

在上下文中我用对象列表初始化数据库

public class KillerContext : DbContext
{
    public DbSet<Killer> Killers { get; set; }
    public DbSet<Contract> Contracts { get; set; }
}

在 Controller 中我这样做:

KillerContext k = new KillerContext();

public ActionResult Index()
{
    var contracts = k.Contracts.ToList();
    ViewBag.contracts = contracts;
    return View();
}

在 Global.asax 中:

Database.SetInitializer(new KillerContextInitialization());

这是我在数据库中输入第一个数据的方式:

public sealed class KillerContextInitialization : DropCreateDatabaseAlways<KillerContext>
{
    protected override void Seed(KillerContext db)
    {
        List<Killer> killers = new List<Killer>();
        //List<Contract> contracts = new List<Contract>();

        killers.Add(new Killer(name: "Ivan Firstein", biography: "He was born in the shadows."));
        killers.Add(new Killer(name: "Oleg Gazmanov", biography: "test man"));
        db.Contracts.Add(new Contract(
                Contract.Status.active,
                killers.SingleOrDefault(x => x.Name == "Ivan Firstein"),
                "KILL OR BE KILLED. As always with love.",
                killers.SingleOrDefault(x => x.Name == "Oleg Gazmanov")
                ));

        db.Killers.AddRange(killers);
        base.Seed(db);
    }
}

Answer 1

看起来您需要为 killer 模型添加 ForeignKey 属性，并将此键存储在属性 ContractId 中:

public class Killer
{
    [ForeignKey(nameof(ContractId)]  //Name of added property in line below
    public Contract Contract { get; set; } //no need "virtual"
    public Guid? ContractId { get; set; }

    // other properties...
}

public class Contract
{
        [ForeignKey("ContractId")] //Name of added property in Killer Model
        public virtual ICollection<Killer> Killers { get; set; }

        // other code... 
}

编辑

您应该执行类似于 Contract.Target 属性的操作:

[ForeignKey(nameof(TargetId)]
public Killer Target { get; set; }
public Guid TargetId { get; set; }

对于枚举类型，你应该像这样添加属性:

[Column(nameof(status), TypeName = "int")]
public Status status { get; set; }