实体框架包括命令 - 向左或内部联接？ [英] Entity framework Include command - Left or inner join?
问题描述
当我正在调查的的区别包括：和加入我发现：
As I was investigating the difference between Include and Join I found that :
如果数据库的不的包括外键 - 它没有导航道具，因此最好使用加入
If the DB does not include a Foreign Keys -it has no navigation props so it's better to use Join
如果它的确实的具有导航道具 - 然后用包含。 （这也节省了分贝命中。）
If It does have a navigation props - then use Include. ( it also save a db hit.)
但有 回答这里 引起了我的注意：
But one answer here caught my attention:
包括被实现为一个连接。 根据空性的 包含的链接是一个内或离开加入。
Include is implemented as a join. Depending on the nullability of the included link it is an inner or left join.
问：
如何在法律上无效影响了左/内部联接？
How does the nullity affects the left / inner join ?
在SQL Server中，我可以有一个城市表和人表，一个人可以有一个 NULL CityID 。
In Sql server I can have a Cities table and Persons table and a person can have a NULL CityID.
为什么做实体框架的决定对我来说是什么样的加入？
Why does entity Framework decides for me what kind of join it is ?
现在，让我们改变CityId不空：
Now lets change CityId to not null :
和这里的变化：
推荐答案
假设在你的类存在于城市或CityID一个 [必需] 的约束。假设有记录的人没有（有效的）城市。只有这样，才能满足 [必需] 是执行内连接。
Suppose that in your class there is a [Required] constraint on City or CityID. And suppose there are Person records without a (valid) City. The only way to satisfy the [Required] is to perform an inner join.
不过，只要你的数据库和模型匹配的约束（即 CityID INT NOT NULL ），它不会真的不管什么样的加入使用。这应该是正常的情况。
But as long as the constraints in your Db and model match (ie CityID INT NOT NULL) it wouldn't really matter what kind of Join is used. That should be the normal case.
和没有约束，你当然会想到左连接。
And without the constraint you would of course expect a Left Join.
这篇关于实体框架包括命令 - 向左或内部联接？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
