重写LINQ外部与方法语法

Question

我有此工作的外部加入查询：

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产生相同的内容。到目前为止，我有：

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

但是，当我需要出版商名称的字符串时，group是IEnumerable。

Answer 1

据我了解，您可以致电

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

Answer 2

我确实设法通过以下内容弄清楚了：

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)});