如何確保EntityRef不能爲空？

Question

我想建立一個簡單的一對多關係，其中一個列表可以有零個或多個任務，並且任務必須有一個關聯的列表。我想用單元測試來保證這種行爲，但我無法弄清楚這個關聯是如何發生的，這樣測試就會失敗（以後我會使用ExpectedExceptionAttribute，但我甚至不知道會拋出哪個異常然而）。

任務即可成功提交，但我希望看到的LINQ抱怨缺少列表參考：

[TestMethod] 
public void SavingTaskWithoutListFails() 
{ 
    var task = new Task() { Title = "Test Task", Description = "This is the task description." }; 
    Db.Tasks.InsertOnSubmit(task); 
    Db.SubmitChanges();    
} 

我的類和關聯是這樣的：

[Table] 
public class Task 
{ 
    [Column(AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY", IsDbGenerated = true)] 
    public int TaskId { get; set; } 

    [Column(IsPrimaryKey = true)] 
    public string Title { get; set; } 

    [Column] 
    public string Description { get; set; } 

    [Column] 
    public int ListId { get; set; } 

    private EntityRef<List> _list; 

    [Association(Storage = "_list", ThisKey = "ListId")] 
    public List List 
    { 
     get { return _list.Entity; } 
     set { _list.Entity = value; } 
    } 
} 

與此：

[Table] 
public class List 
{ 
    [Column(AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY", IsDbGenerated = true)] 
    public int ListId { get; set; } 

    [Column(IsPrimaryKey = true)] 
    public string Title { get; set; } 

    private EntitySet<Task> _tasks; 

    [Association(Storage = "_tasks", OtherKey = "TaskId")] 
    public EntitySet<Task> Tasks 
    { 
     get { return _tasks; } 
     set 
     { 
      if (_tasks == null) 
      { 
       _tasks = new EntitySet<Task>(); 
      } 
      _tasks.Assign(value); 
     } 
    } 
} 

任何人都可以幫助正確的關聯或提示如何實現d行爲？

Answer 1

您應該使用[Column(CanBeNull = false)]作爲關聯列來實現這一點。

編輯：

[Table] 
public class Task 
{ 
    [Column(IsPrimaryKey = true, AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY", IsDbGenerated = true)] 
    public int TaskId { get; set; } 

    [Column] 
    public string Title { get; set; } 

    [Column] 
    public string Description { get; set; } 

    [Column(CanBeNull = false)] 
    public int ListId { get; set; } 

    private EntityRef<List> _list; 

    [Association(Storage = "_list", ThisKey = "ListId", IsForeignKey = true, OtherKey = "ListId")] 
    public List List 
    { 
     get { return _list.Entity; } 
     set { _list.Entity = value; } 
    } 
} 

[Table] 
public class List 
{ 
    [Column(IsPrimaryKey = true, AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY", IsDbGenerated = true)] 
    public int ListId { get; set; } 

    [Column] 
    public string Title { get; set; } 

    private EntitySet<Task> _tasks; 

    [Association(Storage = "_tasks", OtherKey = "TaskId", ThisKey = "ListId")] 
    public EntitySet<Task> Tasks 
    { 
     get { return _tasks; } 
     set 
     { 
      if (_tasks == null) 
      { 
       _tasks = new EntitySet<Task>(); 
      } 
      _tasks.Assign(value); 
     } 
    } 
} 

我搬到IsPrimaryKey到Id，而不是Title兩個表，設置關聯的一側爲IsForeignKey=true和填充都ThisKey和OtherKey爲協會的兩側。當我嘗試添加沒有ListId值的新任務時，SubmitChanges拋出SlqCEException並顯示以下消息：A foreign key value cannot be inserted because a corresponding primary key value does not exist. [ Foreign key constraint name = FK_Task_List ]