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使用EF实现多查询，暂未考虑性能问题
2015年10月6日22:26:51
=====正文=====
我在数据库有三个表，如下图：
sysMenus与sysFunction有主外键关系，而sysUserInfo则与其他二表并无关联。
我现在使用这三个表针对多种情况使用EF实现多种查询手段
方法一： include方法（或EF自身的导航属性）
查询，要的就是出数据罢了。所以我先说EF自身的导航属性，因为这也算常用方法。
我所说的导航属性就是：
模型表下方显示的，可以看到只有拥有主外键关联的表才会有导航属性。
使用起来也特别简单，上代码
直接点出来就是表，真是不要太简单了
而使用include方法则是：
除了多了一个include方法，其他一致的。
区别在于，sql语句生成的不同，使用sql检测工具便知
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方法会inner join 表查询出所有数据，而直接使用导航属性的仅仅只是单表查询（没有连sysMenus表怎么与mName呢？疑问点）
所以我还是使用include
但是没有主外键关系的表模型并没有导航属性，于是include并不能使用在表之间没有主外键关系的表中！
方法二：使用join方法
有主外键关系
生成的sql语句
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]
无主外键关系
sql语句
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语句可知，join也可完美连表，不管两表是否有主外键关联。但join方法有一缺点，无法使用多个join连表，要连三个表怎么做呢？答：join做不到啊
方法三：使用类SQL语句（如何读？）
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]
就像写SQL语句一样，但我感觉跟include是一样的，因为没有导航属性，查出来也用不了
如有错误之处，望各位看管能不吝指出。
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原文地址：http://www.cnblogs.com/hello-mark/p/4858062.html
