Entity Framework 連表查詢 多樣寫法

使用EF實現多查詢，暫未考慮性能問題

2015年10月6日22:26:51

=====正文=====

我在數據庫有三個表，如下圖：

sysMenus與sysFunction有主外鍵關系，而sysUserInfo則與其他二表並無關聯。

 我現在使用這三個表針對多種情況使用EF實現多種查詢手段

方法一： include方法（或EF自身的導航屬性）

　　查詢，要的就是出數據罷了。所以我先說EF自身的導航屬性，因為這也算常用方法。

　　我所說的導航屬性就是：

模型表下方顯示的，可以看到只有擁有主外鍵關聯的表才會有導航屬性。

使用起來也特別簡單，上代碼

 

直接點出來就是表，真是不要太簡單了，但是這樣查詢是有缺點的，因為它不想include方法那樣全部查出來，是當你使用導航屬性點出字段是再去數據庫查一次，因此推薦使用include方法。

 

　　而使用include方法則是：

除了多了一個include方法，其他一致的。

區別在於，sql語句生成的不同，使用sql檢測工具便知

 

SELECT TOP (1) 
    [Extent1].[fID] AS [fID], 
    [Extent1].[mID] AS [mID], 
    [Extent1].[fName] AS [fName], 
    [Extent1].[fFunction] AS [fFunction], 
    [Extent1].[fPicname] AS [fPicname], 
    [Extent1].[fStatus] AS [fStatus], 
    [Extent1].[fCreatorID] AS [fCreatorID], 
    [Extent1].[fCreateTime] AS [fCreateTime], 
    [Extent1].[fUpdateID] AS [fUpdateID], 
    [Extent1].[fUpdateTime] AS [fUpdateTime], 
    [Extent2].[mID] AS [mID1], 
    [Extent2].[mParentID] AS [mParentID], 
    [Extent2].[mName] AS [mName], 
    [Extent2].[mUrl] AS [mUrl], 
    [Extent2].[mArea] AS [mArea], 
    [Extent2].[mController] AS [mController], 
    [Extent2].[mAction] AS [mAction], 
    [Extent2].[mSortid] AS [mSortid], 
    [Extent2].[mStatus] AS [mStatus], 
    [Extent2].[mPicname] AS [mPicname], 
    [Extent2].[mLevel] AS [mLevel], 
    [Extent2].[mExp1] AS [mExp1], 
    [Extent2].[mExp2] AS [mExp2], 
    [Extent2].[mCreatorID] AS [mCreatorID], 
    [Extent2].[mCreateTime] AS [mCreateTime], 
    [Extent2].[mUpdateID] AS [mUpdateID], 
    [Extent2].[mUpdateTime] AS [mUpdateTime]
    FROM  [dbo].[sysFunction] AS [Extent1]
    INNER JOIN [dbo].[sysMenus] AS [Extent2] ON [Extent1].[mID] = [Extent2].[mID]

 

include方法會inner join 表查詢出所有數據，而直接使用導航屬性的僅僅只是單表查詢（沒有連sysMenus表怎么與mName呢？疑問點）

 所以我還是使用include

但是沒有主外鍵關系的表模型並沒有導航屬性，於是include並不能使用在表之間沒有主外鍵關系的表中！

 

方法二：使用join方法

有主外鍵關系

生成的sql語句

SELECT 
    [Extent1].[mID] AS [mID], 
    [Extent1].[mName] AS [mName], 
    [Extent2].[fName] AS [fName]
    FROM  [dbo].[sysMenus] AS [Extent1]
    INNER JOIN [dbo].[sysFunction] AS [Extent2] ON [Extent1].[mID] = [Extent2].[mID]

無主外鍵關系

sql語句

SELECT 
    [Extent1].[mID] AS [mID], 
    [Extent1].[mName] AS [mName], 
    [Extent2].[uLoginName] AS [uLoginName]
    FROM  [dbo].[sysMenus] AS [Extent1]
    INNER JOIN [dbo].[sysUserInfo] AS [Extent2] ON [Extent1].[mID] = [Extent2].[uID]

由生成的SQL語句可知，join也可完美連表，不管兩表是否有主外鍵關聯。但join方法有一缺點，無法使用多個join連表，要連三個表怎么做呢？答：join做不到啊

 

方法三：使用類SQL語句（如何讀？）

SELECT TOP (1) 
    [Extent1].[mID] AS [mID], 
    [Extent1].[mParentID] AS [mParentID], 
    [Extent1].[mName] AS [mName], 
    [Extent1].[mUrl] AS [mUrl], 
    [Extent1].[mArea] AS [mArea], 
    [Extent1].[mController] AS [mController], 
    [Extent1].[mAction] AS [mAction], 
    [Extent1].[mSortid] AS [mSortid], 
    [Extent1].[mStatus] AS [mStatus], 
    [Extent1].[mPicname] AS [mPicname], 
    [Extent1].[mLevel] AS [mLevel], 
    [Extent1].[mExp1] AS [mExp1], 
    [Extent1].[mExp2] AS [mExp2], 
    [Extent1].[mCreatorID] AS [mCreatorID], 
    [Extent1].[mCreateTime] AS [mCreateTime], 
    [Extent1].[mUpdateID] AS [mUpdateID], 
    [Extent1].[mUpdateTime] AS [mUpdateTime]
    FROM   [dbo].[sysMenus] AS [Extent1]
    INNER JOIN [dbo].[sysFunction] AS [Extent2] ON [Extent1].[mID] = [Extent2].[mID]
    INNER JOIN [dbo].[sysUserInfo] AS [Extent3] ON [Extent1].[mID] = [Extent3].[uID]

就像寫SQL語句一樣，但我感覺跟include是一樣的，因為沒有導航屬性，查出來也用不了

 

如有錯誤之處，望各位看管能不吝指出。