Linq-加入混乱 [英] Linq - Join Confusion

问题描述

出于这个问题，我们假设我有表'A'和'B'，并且它们之间存在1:1的关系.在Linq查询中，我可以执行以下操作:

For the sake of this question, let's assume I have tables 'A' and 'B' and there is a 1:1 relationship between them. In a Linq query, I can do the following:

from row in A
where row.B.Description = someValue
select A

其中row.B是对表'B'的引用.

Where row.B is the reference to table 'B'.

但是，现在让我们假设"A"和"B"之间存在1:M的关系.上面的查询不再起作用.看来我需要显式使用"join"，如下所示:

However, let's now assume there is a 1:M relationship between 'A' and 'B'. The above query no longer works. It seems I need to explicitly use 'join' as follows:

from row in A
join row1 in B on row.BId = row1.BId
where row1.Description = someValue
select A

我的问题是这个.对于1:M关系，我是否正确要求加入"?还是有办法在不使用联接的情况下(例如1:1)执行此查询?

My question is this. Am I correct that for 1:M relationships, 'join' is required? Or is there are way to do this query, without using join, like in the 1:1 case?

推荐答案

您不必显式加入，选择很多就可以解决问题

You don't have to join explicitly, select many will do the trick

from row in A   
from row1 in row.B  
where row1.Description == someValue   
select row  

或者(虽然我真的不喜欢)

alternatively (although I really don't like it)

from row in A
where row.B.Any(b => b.Description == someValue)
select row

使用第一个选项时，如果有多个具有相同描述的B，则需要对结果执行Distinct().

With the first option you will need to do a Distinct() on the result if there are many B's that have the same description.

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