將不確定變為確定~DAL層向BLL層返回數據用IEnumerable 還是IQueryable

DAL層從數據庫中將數據讀出來后，傳遞給BLL層，再通過BLL處理數據后，向WEB層返回，最后到頁面上輸出，這是一個過程，在這個過程中我需要說兩句，ＢＬＬ層與ＷＥＢ層通訊肯定是List,IList等等，即實實在在的數據，而ＤＡＬ層向ＢＬＬ層返回數據時，就需要注意了，因為ＤＡＬ層返回一般是完整的結果集，而在ＢＬＬ層根據具體的業務，再進行字段的過濾，這對於減少數據庫與網絡傳遞的壓力是有幫助的，下面是一個案值，分別是向ＢＬＬ層以IEnumerable和IQueryable方式進行數據的返回，最后在ＢＬＬ層進行加工數據的操作，看代碼：

ＤＡＬ層：

IQueryable方式：

 　　　public IQueryable<WebManageUsers> GetWebManageUsers(ISpecification<WebManageUsers> specification)
        {
            var linq = base.GetEntities(specification).AsQueryable()
                           .Include(i => i.WebManageUser_WebManageRoles)
                           .AsQueryable(); //include會增加鏈庫操作
            return linq;
        }

IEnumerable方式：

  public IEnumerable<WebManageUsers> GetWebManageUsers(ISpecification<WebManageUsers> specification)
        {
            var linq = base.GetEntities(specification).AsQueryable()
                           .Include(i => i.WebManageUser_WebManageRoles)
                           .AsQueryable(); //include會增加鏈庫操作
            return linq;
        }

在ＢＬＬ層進行數據重新組裝：

　　　 public List<WebManageUsers> GetWebManageUsers(DateTime? from, DateTime? to, int? status)
        {
            //Create specification
            UserListSpecification dateSpecification = new UserListSpecification(from, to, status);

            return _webManageUsers.GetWebManageUsers(dateSpecification).Select(i => new WebManageUsers_Ext
            {
                CreateDate = i.CreateDate,
                ManageUserID = i.ManageUserID,
                RealName = i.RealName,
            }).ToList<WebManageUsers>();
        }

ＷＥＢ層輸出結果，兩種方式答到的效果是一樣的，但對於一個開發人員來說，只達到效果是遠遠不夠的，因為我們必須要知道ＬＩＮＱ在數據庫上究竟干了什么事，即ＬＩＮＱ被翻譯成ＳＱＬ語句是什么樣的：

IEnumerable方式：

exec sp_executesql N'SELECT 
[Project1].[ManageUserID] AS [ManageUserID], 
[Project1].[LoginName] AS [LoginName], 
[Project1].[Password] AS [Password], 
[Project1].[RealName] AS [RealName], 
[Project1].[Gender] AS [Gender], 
[Project1].[Phone] AS [Phone], 
[Project1].[Mobile] AS [Mobile], 
[Project1].[Email] AS [Email], 
[Project1].[AvatarUrl] AS [AvatarUrl], 
[Project1].[QQ] AS [QQ], 
[Project1].[MSN] AS [MSN], 
[Project1].[Rtx] AS [Rtx], 
[Project1].[Birthday] AS [Birthday], 
[Project1].[Description] AS [Description], 
[Project1].[DepartmentID] AS [DepartmentID], 
[Project1].[CreateDate] AS [CreateDate], 
[Project1].[UpdateDate] AS [UpdateDate], 
[Project1].[Operator] AS [Operator], 
[Project1].[Status] AS [Status], 
[Project1].[IntroductionURL] AS [IntroductionURL], 
[Project1].[WebSystemID] AS [WebSystemID], 
[Project1].[C1] AS [C1], 
[Project1].[ManageUserID1] AS [ManageUserID1], 
[Project1].[ManageRoleID] AS [ManageRoleID], 
[Project1].[CreateDate1] AS [CreateDate1]
FROM ( SELECT 
    [Extent1].[ManageUserID] AS [ManageUserID], 
    [Extent1].[LoginName] AS [LoginName], 
    [Extent1].[Password] AS [Password], 
    [Extent1].[RealName] AS [RealName], 
    [Extent1].[Gender] AS [Gender], 
    [Extent1].[Phone] AS [Phone], 
    [Extent1].[Mobile] AS [Mobile], 
    [Extent1].[Email] AS [Email], 
    [Extent1].[AvatarUrl] AS [AvatarUrl], 
    [Extent1].[QQ] AS [QQ], 
    [Extent1].[MSN] AS [MSN], 
    [Extent1].[Rtx] AS [Rtx], 
    [Extent1].[Birthday] AS [Birthday], 
    [Extent1].[Description] AS [Description], 
    [Extent1].[DepartmentID] AS [DepartmentID], 
    [Extent1].[CreateDate] AS [CreateDate], 
    [Extent1].[UpdateDate] AS [UpdateDate], 
    [Extent1].[Operator] AS [Operator], 
    [Extent1].[Status] AS [Status], 
    [Extent1].[IntroductionURL] AS [IntroductionURL], 
    [Extent1].[WebSystemID] AS [WebSystemID], 
    [Extent2].[ManageUserID] AS [ManageUserID1], 
    [Extent2].[ManageRoleID] AS [ManageRoleID], 
    [Extent2].[CreateDate] AS [CreateDate1], 
    CASE WHEN ([Extent2].[ManageUserID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
    FROM  [dbo].[WebManageUsers] AS [Extent1]
    LEFT OUTER JOIN [dbo].[WebManageUser_WebManageRoles] AS [Extent2] ON [Extent1].[ManageUserID] = [Extent2].[ManageUserID]
    WHERE (@p__linq__0 = 1) AND ([Extent1].[CreateDate] > (CASE WHEN (@p__linq__1 IS NULL) THEN @p__linq__2 ELSE @p__linq__1 END)) AND ([Extent1].[CreateDate] < (CASE WHEN (@p__linq__3 IS NULL) THEN @p__linq__4 ELSE @p__linq__3 END))
)  AS [Project1]
ORDER BY [Project1].[ManageUserID] ASC, [Project1].[C1] ASC',N'@p__linq__0 bit,@p__linq__1 datetime2(7),@p__linq__2 datetime2(7),@p__linq__3 datetime2(7),@p__linq__4 datetime2(7)',@p__linq__0=1,@p__linq__1=NULL,@p__linq__2='0001-01-01 00:00:00',@p__linq__3=NULL,@p__linq__4='9999-12-31 23:59:59.9999999'

IQueryable方式：

exec sp_executesql N'SELECT 
[Extent1].[ManageUserID] AS [ManageUserID], 
[Extent1].[CreateDate] AS [CreateDate], 
[Extent1].[RealName] AS [RealName]
FROM [dbo].[WebManageUsers] AS [Extent1]
WHERE (@p__linq__0 = 1) AND ([Extent1].[CreateDate] > (CASE WHEN (@p__linq__1 IS NULL) THEN @p__linq__2 ELSE @p__linq__1 END)) AND ([Extent1].[CreateDate] < (CASE WHEN (@p__linq__3 IS NULL) THEN @p__linq__4 ELSE @p__linq__3 END))',N'@p__linq__0 bit,@p__linq__1 datetime2(7),@p__linq__2 datetime2(7),@p__linq__3 datetime2(7),@p__linq__4 datetime2(7)',@p__linq__0=1,@p__linq__1=NULL,@p__linq__2='0001-01-01 00:00:00',@p__linq__3=NULL,@p__linq__4='9999-12-31 23:59:59.9999999'

看到這里，您應該有所體會了吧，我們希望的肯定是IQueryable方式的，呵呵，它才是ＬＩＮＱ世界里的延時加載，下面咱們總結一下什么時候用IQueryable方

式來返回數據：

１　結果集很大，需要在ＢＬＬ層去重新組裝時

２　使用take skip實現分頁時