Question

我有这个工作外连接查询：

var outerJoin = from b in books
                join p in publishers on b.PublisherName equals p.Name into joinedPublishers
                from publisher in joinedPublishers.DefaultIfEmpty()
                select new { b.Title, PublisherName = (publisher == null ? "No publisher" : publisher.Name) };

我正在尝试使用方法语法生成相同的内容。到目前为止，我有这个：

outerJoin = books.GroupJoin(publishers, b => b.PublisherName, p => p.Name, (b, group) => new { b.Title, PublisherName = group.DefaultIfEmpty()});

但是，当我需要发布商名称的字符串时，group为IEnumerable。

Answer 1

据我了解你可以致电

{
    b.Title,
    PublisherName = group.Any()?group.First().Name: "No publisher";
}

Answer 2

我确实设法用以下方法解决了这个问题：

outerJoin = books.GroupJoin(publishers, 
                            b => b.PublisherName, 
                            p => p.Name, 
                            (b, publisherGroup) => new { b.Title, publisherGroup})
                 .SelectMany(x => x.publisherGroup.DefaultIfEmpty(), 
                            (x, y) => new {x.Title, PublisherName = (y == null ? "No publisher" : y.Name)});

使用方法语法重写LINQ外连接

2 个答案: