LINQ右连接和左连接

Question

我的任务是将一些T-SQL查询重构为LINQ。简单的join和left outer join很容易理解。这是我的代码：

string[] leftouter = new string[] { "a", "b", "c", "d", "e" };
string[] inner     = new string[] { "a", "b" };

var q = from s1 in leftouter
        join s2 in inner on s1 equals s2 into j
        from sj in j.DefaultIfEmpty() 
        select string.Format("Outer: {0} Left: {1}", s1, sj)

输出结果为：

Outer: a Left: a  
Outer: b Left: b  
Outer: c Left:   
Outer: d Left:   
Outer: e Left:   

这是一个简单的左连接。现在我想添加一个新数据集：

string[] rightouter = new string[] { "c", "d", "e" };  

期望的输出是：

Outer: a Left: a Right:  
Outer: b Left: b Right:  
Outer: c Left:   Right: c
Outer: d Left:   Right: d
Outer: e Left:   Right: e

我该如何重新格式化LINQ以解决这个输出问题？谢谢。

- Franziee

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第一个输出如何包含 e，当 leftouter 和 inner 都不包含 e？ - MarcinJuraszek

似乎是一个打字错误。 - Selman Genç

问题中有错别字吗？您能再编辑一下问题吗？ - qwertymaster

已经完成修正，谢谢。 - Franziee

Answer 1

试试这个：

string[] all = {"a", "b", "c", "d", "e"};
string[] left = {"a", "b"};
string[] right = {"c", "d", "e"};

var q = from innerItem in all
        join leftItem in left on innerItem equals leftItem into leftItems
        join rightItem in right on innerItem equals rightItem into rightItems
        from a in leftItems.DefaultIfEmpty()
        from b in rightItems.DefaultIfEmpty()
        select string.Format("Outer: {0} Left: {1} Right: {2}", innerItem, a, b);

- Frank