如果子外鍵已經存在，則SaveChanges上的DbUpdateException-在Entity Framework代碼中優先

Question

[ 在實體框架5.0 RC中使用代碼優先DbContext ]

具有2個導航屬性/ 2個外鍵的實體

public class Compositon
{

    public string Id { get; set; }

    public string SimpletonId { get; set; }

    [ForeignKey("SimpletonId")]
    public Simpleton Simpleton { get; set; }

    public string CompanitonId { get; set; }

    [ForeignKey("CompanitonId")]
    public Companiton Companiton { get; set; }
}

第一次通過-將更改保存到空數據庫

var composition = new Compositon();
compositon.Id = "UniquePrimaryKey";
var simpleton = new Simpleton();
// This foreign key does not exist in database yet
simpleton.Id = "Simpleton1";
composition.Simpleton = simpleton;
var companiton = new Companiton();
companiton.Id = "SomeOther1";
composition.Companiton = companiton;
// Repositor references the DbContext
Repositor.Compositons.Add(composition);
Repositor.SaveChanges();

第二次通過-現有的孩子外鍵導致父母過錯

var composition = new Compositon();
compositon.Id = "AnotherUniquePrimaryKey";
var simpleton = new Simpleton();
// This foreign key already exists in database
simpleton.Id = "Simpleton1";
composition.Simpleton = simpleton;
var companiton = new Companiton();
companiton.Id = "SomeOther2";
composition.Companiton = companiton;
Repositor.Compositons.Add(composition);
Repositor.SaveChanges();

DbUpdateException: An error occurred while updating the entries.

我需要能夠將這些父類保存到數據庫中，因為它們有時是唯一的，即使它們有時包含已存儲的導航屬性，又該如何保存父類呢？

Answer 1

在第二遍中，您將需要從DbContext檢索現有的Simpleton 。 我猜你可以這樣做：

`simpleton = Repositor.Simpletons.First(s => s.Id == "Simpleton1");`

當前，您正在創建一個全新的實體，實體框架會嘗試將其插入，從而導致密鑰沖突。