首先我们创建2个类，一个Category，一个Product
public class Product
{
public string Name { get; set; }
public int CategoryID { get; set; }
}public class Category { public string Name { get; set; } public int ID { get; set; } }
然后创建2个List的数据源
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}, new Category(){Name="Other", ID=006} }; 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=007}, };好了，现在我们开始使用LINQ了，下面使用的表达式和方法的结果是一样的，这里的方法指Lambda表达式
l 使用排序
1. 使用排序时使用的显示语句
foreach (var c in orderByResult) Console.WriteLine("ID={0},Name={1}", c.ID, c.Name); 2. 升序
表达式
var orderByResult = from c in categories orderby c.ID //默认为升序，也可以在后面加上ascending select c;方法
var orderByResult = categories.OrderBy(c=>c.ID);3. 降序
表达式
var orderByResult = from c in categories orderby c.ID descending select c;方法
var orderByResult = categories.OrderByDescending(c=>c.ID);4. 多个属性的升序
表达式
var orderByResult = from c in categories orderby c.ID,c.Name select c;方法
var orderByResult = categories.OrderBy(c=>c.ID).ThenBy(c=>c.Name);5. 多个属性的降序排列
表达式
var orderByResult = from c in categories orderby c.ID, c.Name descending select c;方法
var orderByResult = categories.OrderByDescending(c=>c.ID).ThenByDescending(c=>c.Name);l 使用Where条件
1. 使用Where的显示语句
foreach (var w in whereResult) Console.WriteLine("ID={0},Name={1}", w.ID, w.Name);2. 单个条件
表达式
var whereResult = from c in categories where c.Name == "Vegetables" select c;方法
var whereResult = categories.Where(c => c.Name == "Vegetables");3. 或条件（sql中的or）
表达式
var whereResult = from c in categories where c.Name == "Vegetables" || c.ID == 001 select c;方法
var whereResult = categories.Where(c => (c.Name == "Vegetables" || c.ID == 001));4. 与条件（sql中的and）
表达式
var whereResult = from c in categories where c.Name == "Vegetables" && c.ID == 001 select c;方法
var whereResult = categories.Where(c => (c.Name == "Vegetables" && c.ID == 001));
l 连接
1. 内连接
表达式，注意在表达式中的使用join时相等要使用equals
var innerJoinQuery = from c in categories join prod in products on c.ID equals prod.CategoryID orderby c.ID select new { CategoryID = c.ID,CategoryName = c.Name, ProductName = prod.Name};方法
var innerJoinQuery = categories.Join(products,//要连接的集合 a=>a.ID ,//第一个集合的主键 b =>b.CategoryID , //第二个集合中和第一个集合的主键关联的键，类型需要和第一个集合的主键相同 (c,d) => //c对应于第一个集合中的对象，d对于与第二个集合中的对象，声明2个变量 new {CategoryID = c.ID,CategoryName = c.Name,ProductName = d.Name} //最终返回的结果类型 ); foreach (var item in innerJoinQuery) { Console.WriteLine("CategoryID = {0},CategoryName={1},ProductName={2}",item.CategoryID, item.CategoryName, item.ProductName); }2. 左连接
表达式
var leftJoinQuery = from c in categories join prod in products on c.ID equals prod.CategoryID into cp from t in cp.DefaultIfEmpty(new Product { Name = "Unknown", CategoryID = 006 }) select new { CategoryID = c.ID, CategoryName = c.Name, ProductName = t.Name }; foreach (var item in leftJoinQuery) { Console.WriteLine("CategoryID = {0},CategoryName={1},ProductName={2}",item.CategoryID, item.CategoryName, item.ProductName); }方法
l 分组
表达式
var groupResults = from c in categories group c by c.ID;var groupResults = categories.GroupBy(c => c.ID); 注意显示时的变化：
foreach (var item in groupResults) { Console.WriteLine(item.Key); foreach (var c in item) { Console.WriteLine(" ID={0},Name={1}", c.ID, c.Name);
} }由于刚开始学习LINQ，对LINQ的理解并不深，难免有不足之处，请大家见谅！
