C# linq 使用或条件连接 3 个表
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linq join 3 tables with or condition
提问by Guillermo Varini
I need to create a statement in LINQ with 3 tables and OR condition.
我需要在 LINQ 中创建一个包含 3 个表和 OR 条件的语句。
My function receives an integer, lets call it intZ. I have 3 tables: tableA, tableBand tableC.
我的函数接收一个整数，让我们调用它intZ。我有 3 个表：tableA,tableB和tableC.
tableAhas columns int1, int2and intB. intBis related to tableB.
tableA有列int1，int2和intB。intB与 相关tableB。
problem:int1or int2of tableAcan be intZand it has to match with one tableCrecord.
问题：int1or int2oftableA可以intZ并且它必须与一个tableC记录匹配。
I need an OR condition, but I have no idea where to place it. Does it go in the where clause? Or in the equals clause?
我需要一个 OR 条件，但我不知道把它放在哪里。它是否在 where 子句中？还是在等号子句中？
At the moment, I know how to join 3 tables, but the condition is killing me.
目前，我知道如何加入 3 个表，但条件正在杀死我。
What is the difference between the two ways to create statements in linq? Is there a performance impact?
在 linq 中创建语句的两种方式有什么区别？有性能影响吗？
edit: Okay, now I think it's more clear. intZhas to be related with intCfrom tableC, and this number can be int1or int2of tableA.
编辑：好的，现在我觉得它更清楚了。intZ必须与intCfrom相关tableC，并且这个数字可以是int1or int2of tableA。
采纳答案by Magnus
Just add it to a Where. In Linq2Sql this will be translated to an inner join (with or) on tableB
只需将其添加到Where. 在 Linq2Sql 中，这将被转换为 tableB 上的内部连接（使用或）
from a in tableA
from b in tableB.Where(x => x.A == a.A || x.B == a.B)
select new { a, b };
回答by Jon Skeet
You can't use an "or" condition in joins in LINQ, as it only supports equijoins. But you should be able to do it in a whereclause with no problems. For example:
您不能在 LINQ 的联接中使用“或”条件，因为它仅支持等值联接。但是你应该能够在where没有问题的子句中做到这一点。例如：
var query = from rowC in tableC
where rowC.intC == intZ
from rowA in tableA
where rowA.int1 == rowC.intC || rowA.int2 == rowC.intC
join rowB in tableB on rowA.intB equals rowB.intB
select new { rowA, rowB, rowC };
回答by Prasanna
This may be helpful.
这可能会有所帮助。
var locations = from r1 in
(from a in context.A
join b in context.B
on a.ID equals b.ID
select new
{
a.Prop1,
a.Prop2,
b.Prop3,
b.ID
})
join c in context.C
on r1.ID equals c.ID
select new
{
r1.Prop1,
r2.Prop2,
r2.Prop3,
c.Prop4
};
回答by K B
For the life of me, I couldn't get the .Where to work in my query (perhaps it's how I'm using LinqPad) but I was able to get the following to work:
对于我的一生，我无法在我的查询中找到 .Where to work（也许这就是我使用 LinqPad 的方式），但我能够使以下内容起作用：
from s in Stores
join a in Areas on s.AreaID equals a.ROWID
join r in Regions on a.RegionID equals r.ROWID
join e in Employees on 1 equals 1 // <-- produces a cartesian product
join t in Titles on e.TitleID equals t.ROWID
where e.AreaID == a.ROWID || e.RegionID == r.ROWID // <--filters the data based on OR stmt
where s.StoreNum == 469
select new { r.RegionName, a.AreaName, s.StoreNum, s.StoreName, t.JobCode, e.FirstName, e.LastName }
回答by Mohit Verma
Try this:-
尝试这个：-
var result= tableA.SelectMany(a => tableB.Where(x => x.A == a.A || x.B == a.B), (a, b) => new {a, b});
