如何從不同的上下文中將實體保存爲NavigationProperty？

Question

我有兩個數據庫表，一個用於Events，一個用於RecurrenceRules。事件具有指向RecurrenceRuleID的FK。

我想要做的就是保存事件，它是來自新上下文的重複規則，但我似乎無法完成此操作。我在想什麼？

using (var context = new ScheduledEventEntities()) 
{ 
    if (obj.EntityKey == null) 
    { 
     context.AddObject(obj.EntityKey.EntitySetName, obj); 
    } 
    else 
    { 
     var existingObject = context.Events.FirstOrDefault(p => p.Ident == obj.Ident); 
     context.ApplyCurrentValues<Event>(obj.EntityKey.EntitySetName, obj); 

     // How do I save obj.RecurrenceRule? 
    } 

    context.SaveChanges(); 
} 

Answer 1

我會嘗試這種方式：

// ... 
var existingObject = context.Events.Include("RecurrenceRule") 
    .FirstOrDefault(p => p.Ident == obj.Ident); 
context.ApplyCurrentValues<Event>(obj.EntityKey.EntitySetName, obj); 

// 1st case: Relationship to RecurrenceRule has been removed or didn't exist 
if (obj.RecurrenceRule == null) 
    existingObject.RecurrenceRule = null; 
// 2nd case: Relationship to RecurrenceRule must be set or updated 
else 
{ 
    // relationship has changed 
    if (existingObject.RecurrenceRule == null || 
     obj.RecurrenceRule.Id != existingObject.RecurrenceRule.Id) 
    { 
     var existingRecurrenceRule = context.RecurrenceRule 
      .SingleOrDefault(r => r.Id == obj.RecurrenceRule.Id); 
     if (existingRecurrenceRule != null) // RecurrenceRule exists in DB 
     { 
      // Update scalar values 
      context.ApplyCurrentValues<RecurrenceRule>(
       obj.RecurrenceRule.EntityKey.EntitySetName, obj.RecurrenceRule); 
     } 
     else // RecurrenceRule does not exist in DB 
     { 
      // nothing to do, SaveChanges will recognize new RecurrenceRule 
      // and create INSERT statement 
     } 
     // set new relationship 
     existingObject.RecurrenceRule = obj.RecurrenceRule; 
    } 
    else // same relationship: just update scalar values 
    { 
     // Update scalar values 
     context.ApplyCurrentValues<RecurrenceRule>(
      obj.RecurrenceRule.EntityKey.EntitySetName, obj.RecurrenceRule); 
    } 
} 

// ... 

的問題確實是ApplyCurrentValues只關心更新標屬性，但不能導航屬性，所以你必須自己處理更新的導航性能。 （不幸的是，更新分離的對象圖幾乎總是會導致這種乏味的代碼，因爲Entity Framework中沒有內置機制來爲您完成這項工作。）