ASP.NET - Linq語法應用 GroupJoin

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昨天在工作上要使用 Linq實踐出資料庫語法的 Left Join，起初我以為我寫過了
參照幾個月前寫的程式碼，結果發現當初是要實踐出 Inner Join，所以又找了一下資料
並且記錄一下，不然我很快就會忘記了

比起一般的linq語法，Lambda我更喜歡，下面會先展示Lambda的寫法

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//先建立兩個類別，之後要組合起來的
class BookId
{
    public int Id { get; set; }
    public string BookType { get; set; }
}

class Book
{
    public int Book_Id { get; set; }
    public string Book_Name { get; set; }
}

//給值
BookId[] myBookId = new BookId[]
{
    new BookId {Id = 1, BookType = "English"},
    new BookId {Id = 2, BookType = "Chinese"}
};

Book[] myBook = new Book[]
{
    new Book { Book_Id = 1, Book_Name = "shit school" },
    new Book { Book_Id = 1, Book_Name = "English is good" },
    new Book { Book_Id = 2, Book_Name = "教你說中文" },
    new Book { Book_Id = 2, Book_Name = "從開始到放棄" },
};

Lambda

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var query = myBookId.GroupJoin(myBook, 
        a => a.Id, b => b.Book_Id, 
        (a, ps) => new { 
            Key = a.BookType, 
            ps = ps 
        });

    foreach (var item in query)
    {
        Response.Write(String.Format("Book Type {0}:", item.Key));

        foreach (var item2 in item.ps )
        {
            Response.Write(item2.Book_Name);
        }
    }

linq

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var result = from a in myBookId
                join b in myBook
                on a.Id
                equals b.Book_Id into ps
                select new {
                    Key = a.BookType,
                    ps = ps
                };

//我懶了

以上 差不多就是這樣

h0 dl3

groupjoin
LINQ自學筆記-語法應用-聚合資料-Join-3、GroupJoin
LINQ自學筆記-語法應用-聚合資料-DefaultIfEmpty 運算子、實做 Left Outer Join 效果
linqsamples

特別感謝

Google

心得

shit

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