c# 泛型应用范例

//---------Queryable<T>,扩展函数查询---------//
//---------Queryable<T>,扩展函数查询---------//

//针对单表或者视图查询

//查询所有
var student = db.Queryable<Student>().ToList();
var studentDynamic = db.Queryable<Student>().ToDynamic();
var studentJson = db.Queryable<Student>().ToJson();

//查询单条
var single = db.Queryable<Student>().Single(c => c.id == 1);
//查询单条没有记录返回空对象
var single2 = db.Queryable<Student>().Where(c => c.id == 1).SingleOrDefault();

//查询第一条
var first = db.Queryable<Student>().Where(c => c.id == 1).First();
var first2 = db.Queryable<Student>().Where(c => c.id == 1).FirstOrDefault();

//取10-20条
var page1 = db.Queryable<Student>().Where(c => c.id > 10).OrderBy(it => it.id).Skip(10).Take(20).ToList();

//上一句的简化写法，同样取10-20条
var page2 = db.Queryable<Student>().Where(c => c.id > 10).OrderBy(it => it.id).ToPageList(2, 10);

//查询条数
var count = db.Queryable<Student>().Where(c => c.id > 10).Count();

//从第2条开始以后取所有
var skip = db.Queryable<Student>().Where(c => c.id > 10).OrderBy(it => it.id).Skip(2).ToList();

//取前2条
var take = db.Queryable<Student>().Where(c => c.id > 10).OrderBy(it => it.id).Take(2).ToList();

// Not like
string conval = "a";
var notLike = db.Queryable<Student>().Where(c => !c.name.Contains(conval.ToString())).ToList();
//Like
conval = "三";
var like = db.Queryable<Student>().Where(c => c.name.Contains(conval)).ToList();

// 可以在拉姆达使用 ToString和 Convert,比EF出色的地方
var convert1 = db.Queryable<Student>().Where(c => c.name == "a".ToString()).ToList();
var convert2 = db.Queryable<Student>().Where(c => c.id == Convert.ToInt32("1")).ToList();//
var convert3 = db.Queryable<Student>().Where(c => DateTime.Now > Convert.ToDateTime("2015-1-1")).ToList();
var convert4 = db.Queryable<Student>().Where(c => DateTime.Now > DateTime.Now).ToList();

//支持字符串Where 让你解决，更复杂的查询
var student12 = db.Queryable<Student>().Where(c => "a" == "a").Where("id>100").ToList();
var student13 = db.Queryable<Student>().Where(c => "a" == "a").Where("id>100 and id in( select 1)").ToList();


//存在记录反回true，则否返回false
bool isAny100 = db.Queryable<Student>().Any(c => c.id == 100);
bool isAny1 = db.Queryable<Student>().Any(c => c.id == 1);


//获取最大Id
object maxId = db.Queryable<Student>().Max(it => it.id);
int maxId1 = db.Queryable<Student>().Max(it => it.id).ObjToInt();//拉姆达
int maxId2 = db.Queryable<Student>().Max<Student, int>("id"); //字符串写法

//获取最小
int minId1 = db.Queryable<Student>().Where(c => c.id > 0).Min(it => it.id).ObjToInt();//拉姆达
int minId2 = db.Queryable<Student>().Where(c => c.id > 0).Min<Student, int>("id");//字符串写法


//order By
var orderList = db.Queryable<Student>().OrderBy("id desc,name asc").ToList();//字符串支持多个排序
//可以多个order by表达示
var order2List = db.Queryable<Student>().OrderBy(it=>it.name).OrderBy(it => it.id, OrderByType.desc).ToList(); // order by name as ,order by id desc

//In
var intArray=new []{"5", "2", "3"};
var intList = intArray.ToList();
var list0 = db.Queryable<Student>().In(it => it.id, 1,2,3).ToList();
var list1 = db.Queryable<Student>().In(it=>it.id, intArray).ToList();
var list2 = db.Queryable<Student>().In("id", intArray).ToList();
var list3 = db.Queryable<Student>().In(it => it.id, intList).ToList();
var list4 = db.Queryable<Student>().In("id", intList).ToList();

//分组查询
var list7 = db.Queryable<Student>().Where(c => c.id < 20).GroupBy(it => it.sex).Select("sex,Count=count(*)").ToDynamic();
var list8 = db.Queryable<Student>().Where(c => c.id < 20).GroupBy(it => it.sex).GroupBy(it=>it.id).Select("id,sex,Count=count(*)").ToDynamic();
List<SexTotal> list9 = db.Queryable<Student>().Where(c => c.id < 20).GroupBy(it => it.sex).Select<Student, SexTotal>("Sex,Count=count(*)").ToList();
List<SexTotal> list10 = db.Queryable<Student>().Where(c => c.id < 20).GroupBy("sex").Select<Student, SexTotal>("Sex,Count=count(*)").ToList();
//SELECT Sex,Count=count(*) FROM Student WHERE 1=1 AND (id < 20) GROUP BY Sex --生成结果