將orderby應用於C＃LINQ內連接

Question

我正在從這個msdn頁面嘗試C＃LINQ Joins。

即使它適用於群組加入，我也無法通過內部聯接應用訂單。

運行查詢的數據是：

    class Product
    {
        public string Name { get; set; }
        public int CategoryID { get; set; }
    }

    class Category
    {
        public string Name { get; set; }
        public int ID { get; set; }
    }

    // Specify the first data source.
    static List<Category> categories = new List<Category>()
    { 
        new Category(){Name="Beverages", ID=001},
        new Category(){ Name="Condiments", ID=002},
        new Category(){ Name="Vegetables", ID=003},
        new Category() {  Name="Grains", ID=004},
        new Category() {  Name="Fruit", ID=005}            
    };

    // Specify the second data source.
    static List<Product> products = new List<Product>()
    {
        new Product{Name="Cola",  CategoryID=001},
        new Product{Name="Tea",  CategoryID=001},
        new Product{Name="Mustard", CategoryID=002},
        new Product{Name="Pickles", CategoryID=002},
        new Product{Name="Carrots", CategoryID=003},
        new Product{Name="Bok Choy", CategoryID=003},
        new Product{Name="Peaches", CategoryID=005},
        new Product{Name="Melons", CategoryID=005},
    };

所需的輸出是 （按括號中的類別列出順序，然后按產品排序）：

Cola(Beverages)
Tea(Beverages)
Mustard(Condiments)
Pickles(Condiments)
Melons(Fruit)
Peaches(Fruit)
Bok Choy(Vegetables)
Carrots(Vegetables)

我能夠使用orderby group-join和orderby以及第二個from-select來生成此輸出，以使組層次結構變形並生成如下的簡單列表：

var listGroupJoinOrderBy =
            from category in categories
            join product in products on category.ID equals product.CategoryID into prodGroup
            from prod in prodGroup
            orderby category.Name, prod.Name  //first order by category name then product name
            select
            new
            {
                Category = category.Name,
                Product = prod.Name
            };

但是后來我無法使用orderby應用於內連接（即沒有into子句的group-join）生成相同的輸出。 我試過以下變種：

變體＃1

var innerJoinOrderBy =
            from category in categories
            orderby category.Name    //orderby category name
            join product in products on category.ID equals product.CategoryID                
            orderby product.Name     //orderby product name
            select
            new
            {
                Category = category.Name,
                Product = product.Name
            };

變種＃2

var innerJoinOrderBy =
            from category in categories

            join product in products on category.ID equals product.CategoryID                
            orderby category.Name, product.Name     //orderby category first and then by product name
            select
            new
            {
                Category = category.Name,
                Product = product.Name
            };    

但是，兩個變體都提供相同的輸出，就像沒有使用orderby ，並產生以下輸出：

Cola (Beverages)
Tea (Beverages)
Mustard (Condiments)
Pickles (Condiments)
Carrots (Vegetables)
Bok Choy (Vegetables)
Peaches (Fruit)
Melons (Fruit)

問：如何使用inner-join和orderby生成所需的輸出？

無論如何，要打印查詢結果，可以使用以下foreach （只需更改查詢變量名稱）：

foreach (var product in simpleInnerJoin)
{
    Console.WriteLine(product.Product + " (" + product.Category + ")");
}

Answer 1

你的第二個選擇應該工作正常

var innerJoinOrderBy =
            from c in categories
            join p in products on c.ID equals p.CategoryID
            orderby c.Name, p.Name
            select new {
                Category = c.Name,
                Product = p.Name
            };

輸出：

[
    { Product="Cola", Category="Beverages" },
    { Product="Tea", Category="Beverages" },
    { Product="Mustard", Category="Condiments" },
    { Product="Pickles", Category="Condiments" },
    { Product="Melons", Category="Fruit" },
    { Product="Peaches", Category="Fruit" },
    { Product="Bok Choy", Category="Vegetables" },
    { Product="Carrots", Category="Vegetables" }
]

從您的輸出中我看到項目按原始順序排列。 確保在查詢中應用了orderby運算符。

Answer 2

將Orderby從主Linq中取出並使用

foreach (var product in simpleInnerJoin.Orderby(i=> i.Category.Name).ThenBy(i=>i.Product.Name))
{
    Console.WriteLine(product.Product + " (" + product.Category + ")");
}

我認為這應該為您提供所需的輸出。