LEFT OUTER JOIN在LINQ [英] LEFT OUTER JOIN in LINQ

问题描述

如何执行左外连接在C＃中的LINQ to对象，而无需使用加入上等号，到条款吗？有没有办法做到这一点与其中，条款？
正确的问题：
对于内部联接是容易的，我有这样的一个解决方案。

 列表＆LT; JoinPair＆GT; innerFinal =（从权利升的左派从r其中L.KEY == r.Key
                             选择新JoinPair {LeftId = l.Id，RightId = r.Id}）
 

但对于左外连接我需要一个解决方案。我的是这样的事情，但它不工作

 名单，LT; JoinPair＆GT; leftFinal =（由L在权利从研发左派
                             选择新JoinPair {
                                            LeftId = l.Id，
                                            ？RightId =（（L.KEY == r.Key）r.Id：0
                                        }）
 

其中JoinPair是一个类：

 公共类JoinPair {长leftId;长rightId; }
 

解决方案

由于上注明：

101 LINQ示例 - LEFT OUTER JOIN

 变种Q =
    从C类
    加入产品P的c.Category等于p.Category为PS
    从ps.DefaultIfEmpty P（）
    选择新{类别= C，产品名称= P == NULL？ （无产品）：p.ProductName};
 

How to perform left outer join in C# LINQ to objects without using join-on-equals-into clauses? Is there any way to do that with where clause? Correct problem: For inner join is easy and I have a solution like this

List<JoinPair> innerFinal = (from l in lefts from r in rights where l.Key == r.Key
                             select new JoinPair { LeftId = l.Id, RightId = r.Id})

but for left outer join I need a solution. Mine is something like this but it's not working

List< JoinPair> leftFinal = (from l in lefts from r in rights
                             select new JoinPair { 
                                            LeftId = l.Id, 
                                            RightId = ((l.Key==r.Key) ? r.Id : 0
                                        })

where JoinPair is a class:

public class JoinPair { long leftId; long rightId; }

解决方案

As stated on:

101 LINQ Samples - Left outer join

var q =
    from c in categories
    join p in products on c.Category equals p.Category into ps
    from p in ps.DefaultIfEmpty()
    select new { Category = c, ProductName = p == null ? "(No products)" : p.ProductName };

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