在JOIN子句中使用OR条件进行LINQ查询 [英] LINQ Query Using OR Condition in JOIN Clause

问题描述

注意: C#或VB.NET的答案都可以，但是我的问题将在VB.NET中...

我一直在尝试将以下SQL转换为LINQ to Entity语句:

Note: C# or VB.NET answers are fine, but my question will be in VB.NET...

I have been trying to convert the following SQL into a LINQ to Entity statement:

SELECT
	*
FROM Person
JOIN Company
	ON Person.CompanyName = Company.CompanyName
	OR
	(
		Person.CompanyName = 'Unemployed'
		AND Company.VolunteerJob = 1
	)

但是，LINQ似乎在JOIN子句中不支持OR运算符.我的一位同事建议我使用UNION，我明天将尝试使用UNION，但我想知道是否还有更明显的语法.为了澄清，这就是我要做的(语法不支持此操作):

However, LINQ does not seem to support the OR operator in JOIN clauses. A coworker of mine helpfully suggested I use a UNION, which I will try tomorrow, but I''d like to know if there is a more obvious syntax. To clarify, this is what I am trying to do (the syntax does not support this):

Dim results =
    From Person In context.Person
    Join Company In context.Company
        On Person.CompanyName Equals Company.CompanyName Or
        (Person.CompanyName Equals "Unemployed" And Company.VolunteerJob = 1)

请注意，我真正使用的表/字段与上面的内容完全不同...我只是在上面用于演示目的.

Note that the tables/fields I am really using are nothing like the above... I am just using them above for demonstration purposes.

推荐答案

我有两种方法我正在考虑，但在决定之前我必须研究一下性能.一种方法将所有条件放在WHERE子句中，另一种方法UNION将两个初始结果集组合在一起.

There are two approaches I am considering, but I have to look into the performance before I decide. One approach puts all the conditions in the WHERE clause, and the other approach UNIONs two initial result sets.

' Get all companies in one LINQ query.
Dim combinedCompanies =
	From P in context.Person
	From C in context.Company
	Where
		C.CompanyName Equals P.CompanyName
		And P.CompanyName <> "Unemployed"
		Or
		(
			P.CompanyName = "Unemployed" And
			C.VolunteerJob = True
		)

这是我的同事推荐的版本:

This is the version that my coworker recommended:

' Join with normal companies.
Dim matchingCompanies =
	From P In context.Person
	Join C In context.Company
		On C.CompanyName Equals P.CompanyName
	Where
		P.CompanyName <> "Unemployed"

' Join with volunteer companies.
Dim volunteerCompanies =
	From P In context.Person
	From C In context.Company
	Where
		P.CompanyName = "Unemployed" And
		C.VolunteerJob = True

' Combine normal and volunteer companies.
Dim combinedCompanies = matchingCompanies.Union(volunteerCompanies)

我喜欢第一种方法的简洁性，但是我不确定它是否会像第二种方法那样高效.

I like the brevity of the first approach, but I''m not sure it will be as performant as the second approach.

尝试从这里使用LINQ pad [ ^ ]

OR写为||在LINQ

还要检查此 [

Hi,

try using LINQ pad from here[^]

OR is written as || in LINQ

also check this[^]

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