asp.net mvc linq清理數據庫調用

Question

var Dic = _db.Dictionaries.Single(m => m.int_DictionaryId == id); 
    var DicRef = Dic.DictionaryRefs.Where(m => m.int_DictionaryId == id); 

第二個會調用數據庫還是會基於Dic？

Answer 1

這取決於。你可以配置你的DataContext進行延遲加載（在需要時進行數據庫調用）或急切加載（一次加載所有內容）。 LINQ到SQL使用延遲加載（或延遲加載）默認：

using (YourDataContext _db = new YourDataContext()) 
{ 
    // This will no load any child object/collection. They are requested 
    // when needed. 
    var Dic = _db.Dictionaries.Single(m => m.int_DictionaryId == id); 

    // Now the DictionaryRefs get loaded from the database 
    var DicRef = Dic.DictionaryRefs.Where(m => m.int_DictionaryId == id).ToList(); 

    // Now the DisplayModes get loaded from the database 
    var DicDisplay = Dic.DisplayModes.Where(m => m.DisplayID = displayId).ToList(); 
} 

您可以關閉延遲加載完全關閉：

using (YourDataContext _db = new YourDataContext()) 
{ 
    _db.DeferredLoadingEnabled = false; 

    // This will load the DictionaryRefs child collection 
    // (and any other child object/collection of Dictionary) as well 
    var Dic = _db.Dictionaries.Single(m => m.int_DictionaryId == id); 

    // No call to the database is needed. DictionaryRefs are already loaded 
    var DicRef = Dic.DictionaryRefs.Where(m => m.int_DictionaryId == id).ToList(); 

    // No call to the database is needed. DisplayModes are already loaded 
    var DicDisplay = Dic.DisplayModes.Where(m => m.DisplayID = displayId).ToList(); 
} 

或者，你可以離開延遲加載，並告訴你的DataContext到熱切僅加載一些關係：

using (YourDataContext context = new YourDataContext()) 
{ 
    DataLoadOptions options = new DataLoadOptions(); 
    options.LoadWith<Dictionary>(d => d.DictionaryRefs); 

    context.LoadOptions = options; 

    // This will load the DictionaryRefs child collection as well, 
    // but other child objects/collection will not me loaded 
    var Dic = _db.Dictionaries.Single(m => m.int_DictionaryId == id); 

    // No call to the database is needed. DictionaryRefs are already loaded 
    var DicRef = Dic.DictionaryRefs.Where(m => m.int_DictionaryId == id).ToList(); 

    // Now the DisplayModes get loaded from the database 
    var DicDisplay = Dic.DisplayModes.Where(m => m.DisplayID = displayId).ToList(); 
} 

使用這些選項，您可以控制對象如何相關的加載和accesse d。還請注意，我要求每個兒童收藏都採用ToList()方法。這是因爲當實際需要訪問查詢時，LINQ to SQL只會調用數據庫。

例如：

using (YourDataContext _db = new YourDataContext()) 
{ 
    var comments = _db.Comments.Where(c => c.PostID = 5); 

    // At this point, no call has been made to the database yet. 

    // Now the database is called, because you want to use the comments 
    foreach(var comment in comments) 
    { 
     ... 
    } 
} 

Answer 2

加總，以迫使它運行。

var DicRef = Dic.DictionaryRefs.Where(m => m.int_DictionaryId == id).ToList();