我正在尝试使用这个msdn页面中的C# LINQ Joins。
虽然在组合连接中可以使用,但我无法对内部连接应用order by。
运行查询的数据如下:
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},
};
期望的输出结果是(按括号中的类别和产品排序):
Cola(Beverages)
Tea(Beverages)
Mustard(Condiments)
Pickles(Condiments)
Melons(Fruit)
Peaches(Fruit)
Bok Choy(Vegetables)
Carrots(Vegetables)
我使用group-join
、orderby
和第二个from-select
来生成以下输出,以形成组层次结构并生成普通列表:
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,当我在内连接(即没有使用into
子句的组连接)中应用orderby
时,就无法生成相同的输出。我尝试了以下几种变体:
变体#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
};
变体#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
};
然而,两种变体的输出结果与不使用orderby
时相同,并产生以下输出:
Cola (Beverages)
Tea (Beverages)
Mustard (Condiments)
Pickles (Condiments)
Carrots (Vegetables)
Bok Choy (Vegetables)
Peaches (Fruit)
Melons (Fruit)
问:如何使用inner-join
和orderby
生成所需的输出?
无论如何,要打印查询结果,可以使用以下foreach
(只需更改查询变量名称):
foreach (var product in simpleInnerJoin)
{
Console.WriteLine(product.Product + " (" + product.Category + ")");
}
orderby
运算符。 - Sergey Berezovskiy