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以下情况：存在一个数组作为交叉表（mergeSet）。此外，还存在一组目标值和一组源值。源值可以通过交叉表与目标值连接。- 但是，如何仅使用一个 LINQ 表达式来表达例如 targetSet 与其他表的外连接？

目前我只找到了使用多个 LINQ 表达式的解决方案（即 targetSet+mergeSet+sourceSet 的内部连接，然后是纯左外部部分，最后是 innerJoinResult 和 outerPart 的串联）。

        var mergeSet = new[] 
        {
            new KeyValuePair<int, int>(3, 4), 
            new KeyValuePair<int, int>(5, 6)
        };

        var targetSet = new[] { 1, 3, 5, 7 };
        var sourceSet = new[] { 4, 6 };

        var innerJoinResult =
          from mergeItem in mergeSet
          join sourceItem in sourceSet on mergeItem.Value equals sourceItem
          join targetItem in targetSet on mergeItem.Key equals targetItem
          group sourceItem by targetItem;

        var outerPart =
            from targetItem in targetSet
            where !mergeSet.Any(mergeItem => mergeItem.Key == targetItem)
            group 0 by targetItem; // Fill the right part with zero.

        var outerJoinResult = outerPart.Concat(innerJoinResult);
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1 回答 1

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以下代码：

    var outerJoinResult =
        (from ti1 in targetSet
         join mi1 in mergeSet on ti1 equals mi1.Key into joinedMerge
         from jm1 in joinedMerge.DefaultIfEmpty()
         join si1 in sourceSet on jm1.Value equals si1 into joinedSource
         from js1 in joinedSource.DefaultIfEmpty()
         select new { target = ti1, source = js1 }).ToList();

    outerJoinResult.ForEach(x => Console.Out.WriteLine("Source: {0}, Target: {1}", x.source, x.target));

打印：

Source: 0, Target: 1
Source: 4, Target: 3
Source: 6, Target: 5
Source: 0, Target: 7
于 2010-10-26T01:29:00.033 回答