Question

所以我有这些模型：

ParentModel.cs

public class ParentModel {
  ...properties here

  //relationship to Child
  [ForeignKey("ChildModelID")]
  public ChildModel ChildModel { get; set; }
}

ChildModel.cs

public class ChildModel{
  ...properties here

  //relationship to parent
  [ForeignKey("ParentModel")]
  public int? ParentModelID { get; set; }
  public ParentModel ParentModel { get; set; }
}

我正在使用Web API Code-first。我是新来的。我在创建数据库时收到以下错误。但是，如果我删除ParentModel中的导航属性（即public ChildModel ChildModel { get; set; }），一切正常，但它不能满足我的需要。当我得到ParentModel时，我想急切加载（或懒加载不确定哪个术语是正确的）ChildModel。这里的关系是零或一对一。这意味着ChildModel可以拥有一个在ParentModel中没有引用的记录。

Multiplicity is not valid in Role 'ChildModel_ParentModel_Source' in relationship 
'ChildModel_ParentModel'. Because the Dependent Role properties are not the key 
properties, the upper bound of the multiplicity of the Dependent Role must 
be '*'.

提前谢谢！

Answer 1

ChildModel和ParentModel是One-to-Zero / One

更新：

所以试试这段代码

public class ChildModel
{
    public int Id { get; set; }
    public ParentModel ParentModel { get; set; }
}

public class ParentModel
{
    //[ForeignKey("ChildModel")]
    //[Key]
    public int ChildModelId { get; set; }
    public ChildModel ChildModel { get; set; }
}

public class Context : DbContext
{
    public DbSet<ChildModel> ChildModels { get; set; }
    public DbSet<ParentModel> ParentModels { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<ParentModel>().HasKey(s => s.ChildModelId);

        modelBuilder.Entity<ParentModel>().HasRequired(s => s.ChildModel).WithOptional(s => s.ParentModel);
    }
}

Answer 2

我认为你混淆了ForeignKey属性。不应该在ParentModel上并参考ParentModelID？

public class ChildModel
{
    ...properties here

    //relationship to parent
    public int? ParentModelID { get; set; }
    [ForeignKey("ParentModelID")]
    public ParentModel ParentModel { get; set; }
}

首先在C＃代码中配置关系

2 个答案: