asp.net mvc linq清理数据库调用

Question

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

第二个会调用数据库还是会基于Dic？

Answer 1

这取决于。你可以配置你的DataContext进行延迟加载（在需要时进行数据库调用）或急切加载（一次加载所有内容）。 LINQ到SQL使用延迟加载（或延迟加载）默认：

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(); 
} 

您可以关闭延迟加载完全关闭：

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，你可以离开延迟加载，并告诉你的DataContext到热切仅加载一些关系：

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(); 
} 

使用这些选项，您可以控制对象如何相关的加载和accesse d。还请注意，我要求每个儿童收藏都采用ToList()方法。这是因为当实际需要访问查询时，LINQ to SQL只会调用数据库。

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

加总，以迫使它运行。

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