基于Dapper的开源Lambda超轻量扩展，Dapper.Common

  public class User
    {
        /// <summary>
        /// name:用于映射字段名和数据库字段不一致
        /// key:
        ///     目前实现了Primary的定义，设置为Primary的字段update实体时，默认采用该字段为更新条件
        /// isIdentity：
        ///     设置未true时在Insert时不会向该字段设置任何值
        /// isColumn:
        ///     标识该字段是否在数据库存在，用于扩展User而不在sql中生成该字段
        /// </summary>
        [Column(name: "id", key: ColumnKey.Primary, isIdentity: true, isColumn: true)]
        public int? Id { get; set; }
        [Column(name:"nick_name")]
        public string NickName { get; set; }
        [Column(name: "create_time")]
        public DateTime? CreateTime { get; set; }
    }

//在App启动时执行一次即可
SessionFactory.AddDataSource(new DataSource()
{
    Name = "mysql",
    Source = () => new SqlConnection("connectionString"),
    SourceType = DataSourceType.SQLSERVER,
    UseProxy = true//使用Session的静态代理实现，记录日志，执行耗时
});
//获取数据库上下文
using (var session = SessionFactory.GetSession("msql"))
{
    //linq to sql
}

var entity = new User()
{
    CreateTime=DateTime.Now,
    NickName="dapper",
};
//绝大部分接口可以设置condition已决定是否执行，支持批量更新
session.From<User>().Insert(entity,condition:1>2);
//查看日志
var loggers = session.Loggers;

 //更新所有字段（where id=2），支持批量
 session.From<User>().Update(entity);

 //更新部分字段
 session.From<User>()
     .Set(a => a.NickName, "李四", condition: true)//condition为true时更新该字段
     .Set(a => a.Balance, a => a.Balance + 100)//余额在原来基础增加100
     .Where(a => a.Id.In(1,2,3))//将id为1，2，3的记录进行更新
     .Update();

  //删除id>5||nick_name like ‘%da%‘
  session.From<User>()
      .Where(a=>a.Id>5||a.NickName.Like("da"))
      .Delete();

  //查询全部字段
  var user1 = session.From<User>()
      .Where(a=>a.Id==2)
      .Single();
 
  //查询部分字段
  var user2 = session.From<User>()
     .Where(a => a.Id == 2)
     .Single(s=>new
     {
         s.Id,
         s.NickName
     });

 //查询:where id in(1,2,3)
 var list = session.From<User>()
        .Where(a => a.Id.In("1,2,3".Split(‘,‘)))
        .Select();

 //构建动态查询，condition: true执行，多个where之间用 and 连接
 var list = session.From<User>()
        .Where(a => a.Id.In(1, 2, 3), condition: true)
        .Where(a => a.NickName.Like("da"), condition: false)
        .Where(a => a.Id > 2 || (a.NickName.Like("da") && a.Balance > 50))
        .Where("select * from user_bill where user_bill.user_id=user.id")//同样可以当作字符串拼接工具
        .Select();

 /// <summary>
 /// 自定义函数
 /// </summary>
 public static class MySqlFun
 {
     //这里使用泛型并不是必须的，只用函数名在数据库存在即可，泛型为了指定返回数据类型
     [Function]//Dapper.Common严格区分C#函数和数据库函数，一定要用该特性标识数据库函数
     public static T COUNT<T>(T column)
     {
         return default(T);
     }
     [Function]
     public static T MAX<T>(T column)
     {
         return default(T);
     }
     [Function]
     public static T DISTINCT<T>(T column)
     {
         return default(T);
     }

 //构建动态查询，condition: true执行，多个where之间用 and 连接
 var list = session.From<Order>()
     .GroupBy(a => a.UserId)
     .Having(a => MySqlFun.COUNT(MySqlFun.DISTINCT(a.UserId)) > 10)//count(distinct(user_id))>10
     .Select(s => new
     {
         s.UserId,
         OrderCount = MySqlFun.COUNT(1L),//这里应该返回long int，
         MaxFee = MySqlFun.MAX(s.TotalFee)
     });

 var list = session.From<Order, User>()
     .Join((a, b) => a.UserId == b.Id, JoinType.Inner)
     .GroupBy((a, b) => a.UserId)
     .Having((a, b) => MySqlFun.COUNT(MySqlFun.DISTINCT(a.UserId)) > 10)//count(distinct(user_id))>10
     .Select((a, b) => new
     {
         a.UserId,
         b.NickName,
         OrderCount = MySqlFun.COUNT(1L),//这里应该返回long int，
         MaxFee = MySqlFun.MAX(a.TotalFee)
     });

var list = session.From<Order>()
    .GroupBy(a  => a.UserId)
    .Having(a => MySqlFun.COUNT(MySqlFun.DISTINCT(a.UserId)) > 10)
    .Select(a => new
    {
        a.UserId,
        UserName=Convert.ToString("select nick_name from user where user.id=order.user_id"),//如果这个子查询返回的是int：Convert.ToInt32(sq)
        OrderCount = MySqlFun.COUNT(1L),//这里应该返回long int，
        MaxFee = MySqlFun.MAX(a.TotalFee)
    });

  //获取数据库上下文
  ISession session = null;
  try
  {
      //开启事务
      session.Open(true);
      //sql
      //提交事务
      session.Commit();
  }
  catch (Exception)
  {
      session?.Rollback();
      throw;
  }
  finally
  {
      session?.Close();
  }