LinqToSql初探

Posted 2020-08-10

LINQ TO SQL是一种轻量级的ORM框架，它对ADO.NET进行了轻量级的封装，讲数据库原封不动的映射成模型，常用于中小型项目，优点：简单。缺点：数据库模型过于复杂时,可能不满足开发要求。

 

LINQ语句:

简单类型查询(string):

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LINQ
{
    class Program
    {
        public  delegate int[] generateLotsOfNumbers(int count);//产生大量随机数
        static void Main(string[] args)
        {

            string[] names ={"Alonso","Zheng","Smith","Jones","Smythe","Small","Ruiz","Hsieh","Jorgenson",
                               "Ilyich","Singh","Samba","Fatimah"};
            var queryResult1 = from n in names select n;//遍历操作
            var queryResult2 = names;//lambda表达式，功能同1
            var queryResult3 = from n in names where n.StartsWith("S") select n;//查询以S开头
            var queryResult4 = names.Where(n => n.StartsWith("S"));// lambda表达式，功能同3
            var queryResult5 = from n in names where n.StartsWith("S") orderby n select n;//升序
            var queryResult6 = from n in names where n.StartsWith("S") orderby n descending select n;//降序
            var queryResult7 = names.OrderBy(n => n).Where(n => n.StartsWith("S"));//lambda表达式,功能同4
            var queryResult8 = names.OrderByDescending(n => n).Where(n => n.StartsWith("S"));//功能同5

            //查询大型数据集
            generateLotsOfNumbers ge = delegate(int count) //匿名函数
            {
                Random generator = new Random(0);
                int[] result = new int[count];
                for(int i=0;i<count;i++)
                {
                    result[i] = generator.Next();
                }
                return result;
            };
            int[] numbers = ge(12345678);
            var queryResult9 = from n in numbers where n < 1000 select n;//条件查找
            var queryResult10 = numbers.Where(n => n < 1000);//lambda表达式，功能同9

            //聚合运算符
            Console.WriteLine(queryResult9.Count());//数量
            Console.WriteLine(queryResult9.Min());
            Console.WriteLine(queryResult9.Max());
            Console.WriteLine(queryResult9.Average());
            Console.WriteLine(queryResult9.Sum());

        }
    }
}

 

复杂类型查询:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LINQ
{
    class Customer
    {
        public string ID { get; set; }
        public string City { get; set; }
        public string Country { get; set; }
        public string Region { get; set; }
        public decimal Sales { get; set; }

        public override string ToString()
        {
            return "ID: " + ID + " City: " + City + " Country: " + Country + " Region: " + Region + " Sales: " + Sales;
        }
    }
    class Program
    {
        public static void Main(string[] args)
        {
            List<Customer> customers = new List<Customer> {
              new Customer { ID="A", City="New York", Country="USA", Region="North America", Sales=9999},
              new Customer { ID="B", City="Mumbai", Country="India", Region="Asia", Sales=8888},
              new Customer { ID="C", City="Karachi", Country="Pakistan", Region="Asia", Sales=7777},
              new Customer { ID="D", City="Delhi", Country="India", Region="Asia", Sales=6666},
              new Customer { ID="E", City="São Paulo", Country="Brazil", Region="South America", Sales=5555 },
              new Customer { ID="F", City="Moscow", Country="Russia", Region="Europe", Sales=4444 },
              new Customer { ID="G", City="Seoul", Country="Korea", Region="Asia", Sales=3333 },
              new Customer { ID="H", City="Istanbul", Country="Turkey", Region="Asia", Sales=2222 },
              new Customer { ID="I", City="Shanghai", Country="China", Region="Asia", Sales=1111 },
              new Customer { ID="J", City="Lagos", Country="Nigeria", Region="Africa", Sales=1000 },
              new Customer { ID="K", City="Mexico City", Country="Mexico", Region="North America", Sales=2000 },
              new Customer { ID="L", City="Jakarta", Country="Indonesia", Region="Asia", Sales=3000 },
              new Customer { ID="M", City="Tokyo", Country="Japan", Region="Asia", Sales=4000 },
              new Customer { ID="N", City="Los Angeles", Country="USA", Region="North America", Sales=5000 },
              new Customer { ID="O", City="Cairo", Country="Egypt", Region="Africa", Sales=6000 },
              new Customer { ID="P", City="Tehran", Country="Iran", Region="Asia", Sales=7000 },
              new Customer { ID="Q", City="London", Country="UK", Region="Europe", Sales=8000 },
              new Customer { ID="R", City="Beijing", Country="China", Region="Asia", Sales=9000 },
              new Customer { ID="S", City="Bogotá", Country="Colombia", Region="South America", Sales=1001 },
              new Customer { ID="T", City="Lima", Country="Peru", Region="South America", Sales=2002 }
           };

            var queryResult1 = from c in customers where c.Region == "Asia" select c; //条件查询
            var queryResult2 = customers.Where(c => c.Region == "Asia");//lambda表达式,功能同1

            //创建新对象
            var queryResult3 = from c in customers where c.Region == "North America" 
                               select new { c.City, c.Country, c.Sales };//创建新对象
            var queryResult4 = customers.Where(c => c.Region == "North America").
                Select(c => new { c.City, c.Country, c.Sales });//lambda表达式，功能同3(注意此处调用顺序)

            //Distinct()
            var queryResult5 = (from c in customers select c.Region).Distinct();//查找出不重复的地区
            var queryResult6 = customers.Select(c => c.Region).Distinct();//lambda表达式, 功能同5

            //ALL和ANY
            bool anyUSA = customers.Any(c => c.Country == "USA");//是否存在USA的客户
            bool allAisa = customers.All(c => c.Region == "Asia");//是否全是Aisa客户

            //多级排序
            var queryResult7 = from c in customers
                               orderby c.Region, c.Country, c.City
                               select new { c.ID, c.Region, c.Country, c.City };
            //升降序(ThenBy和ThenByDescending在OrderBy之后)
            var queryResult8 = customers.OrderBy(c => c.Region).ThenByDescending(c => c.Country).
                               ThenBy(c => c.City).Select(c => new { c.ID, c.Region, c.Country, c.City });

            //组合查询
            var queryResult9 = from c in customers group c by c.Region 
                               into cg select new { TotalSales = cg.Sum(c => c.Sales), Regioin = cg.Key };
            var queryResult10 = from cg in queryResult9 orderby cg.TotalSales descending select cg;//各区域消费总额排名
           

            //Take() Skip()
            queryResult9.Take(5);//前五
            queryResult9.Skip(5);//跳过前五

            //First() FirstOrDefault()
            queryResult9.First();
            queryResult9.FirstOrDefault();

            //集运算符
            //Interserct();Except();Union();

            //Join
            var queryResults =
               from c in customers
               join o in orders on c.ID equals o.ID
               select new { c.ID, c.City, SalesBefore = c.Sales, NewOrder = o.Amount, SalesAfter = c.Sales + o.Amount };
        }
    }
}

 

LINQTOSQL:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Saku
{
    class Program
    {
        private static DataClasses1DataContext dataContext = new DataClasses1DataContext();
        public  static List<Teacher> stu = new List<Teacher>();
        static void Main(string[] args)
        {
            var queryResult = from c in dataContext.Teacher where c.tID == "0001" select c;
            var queryResult1 = dataContext.Teacher.Where(c => c.tID == "0001");

            foreach(var item in queryResult1)
            {
                Console.WriteLine(item.tName);
            }
        }
        static Teacher Add(Teacher t)//增
        {
            dataContext.Teacher.InsertOnSubmit(t);
            dataContext.SubmitChanges();
            return t;
        }



        static Teacher Delete(Teacher t)//删除
        {
            dataContext.Teacher.DeleteOnSubmit(t);
            dataContext.SubmitChanges();
            return t;
        }


        static void Show()//遍历
        {
            foreach (Teacher tch in dataContext.Teacher)
            {
                Console.WriteLine(tch.tID + " " + tch.tName + " " + tch.tPassword + " " + tch.tPhone + " " + tch.tAcademy + " " + tch.tDepartment + " " + tch.tRole);
            }
        }

        static bool Search(Teacher t)//查找
        {
            var queryResult = from n in dataContext.Teacher where n.tID == t.tID select n;
            if(queryResult!=null)
            {
                Console.WriteLine("找到" + t.tID);
                return true;
            }
            else
            {
                Console.WriteLine("没找到" + t.tID);
                return false;
            }
        }

        static void change()//改
        {
            var t = dataContext.Teacher.SingleOrDefault(c => c.tID == "0001");
            t.tPhone = "13437196351";
            dataContext.SubmitChanges();

        }

    }
}

 

未完待续。。