轻量级高性能ORM框架：Dapper高级玩法

Dapper高级玩法1：

数据库中带下划线的表字段自动匹配无下划线的Model字段。

Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true;

备注：

这个对使用Mysql数据库的朋友最有帮助，因为Mysql默认都是小写，一般字段都带下划线，比如：user_name之类。

具体效果如下演示

1，首先创建一张表并插入数据

2，创建Model模型

public class User
    {
        public int UserID { get; set; }
 
        public string UserName { get; set; }
 
        public int RoleID { get; set; }
    }

3，扩写抽取数据逻辑代码.

select * from [user]

static Program()
        {
            var config = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
 
            var data = config.Build();
            DapperExtension.DBConnectionString = data.GetConnectionString("DefaultConnection");
        }
 
        static void Main(string[] args)
        {
            IDbConnection dbconnection = null;
 
            using (dbconnection = dbconnection.OpenConnection())
            {
                var users = dbconnection.List("select * from [user]", null);
                foreach (var user in users)
                {
                    Console.WriteLine($"{user.UserID}-{user.UserName}-{user.RoleID}");
                }
            }
 
            Console.ReadKey();
        }

4，无MatchNamesWithUnderscores设置时的数据抽取

没有绑定成功？？

这是因为用了Select * from的缘故，取出来的字段是带下划线的与Model的字段不匹配。

5，设置MatchNamesWithUnderscores再次数据抽取

static void Main(string[] args)
        {
            Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true;
            IDbConnection dbconnection = null;
            using (dbconnection = dbconnection.OpenConnection())
            {
                var users = dbconnection.List("select * from [user]", null);
                foreach (var user in users)
                {
                    Console.WriteLine($"{user.UserID}-{user.UserName}-{user.RoleID}");
                }
            }
 
            Console.ReadKey();
        }

数据绑定成功。

就一句Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true，让我们少写了不少AS语句。

Dapper高级玩法2：

法力无边的Query,由于带有Function功能，可以自由设置模型绑定逻辑。

1，创建两张有关联的表，并填入数据。

2，抽取user和它关联的role数据。

select 1 as table1,T1.*,1 as table2,T2.* from [user] T1 inner join [role] T2 on T1.role_id = T2.role_id

扩展方法：

public static IEnumerable QueryT(this IDbConnection dbconnection, string sql, Func map, object param = null, IDbTransaction transaction = null, string splitOn = "Id")
        {
            return dbconnection.Query(sql, map, param, transaction, splitOn: splitOn);
        }

使用：

static void QueryTest()
        {
            Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true;
            IDbConnection dbconnection = null;
            using (dbconnection = dbconnection.OpenConnection())
            {
                var result = dbconnection.QueryT(
                    @"select 1 as table1,T1.*,1 as table2,T2.* from [user] T1 inner join [role] T2 on T1.role_id = T2.role_id",
                    (user, role) =>
                    {
                        user.Role = role;
                        return user;
                    },
                    null,
                    splitOn: "table1,table2");
 
                foreach (var user in result)
                {
                    Console.WriteLine($"{user.UserID}-{user.UserName}-{user.Role.RoleID}-{user.Role.RoleName}");
                }
            }
            Console.ReadKey();
        }

成功取到数据。

splitOn解释：模型绑定时的字段分割标志。table1到table2之间的表字段绑定到User，table2之后的表字段绑定到Role。

3，特殊Function逻辑。比如抽取role_id对应的user一览。

select 1 as table1,T1.*,1 as table2,T2.* from [role] T1 left join [user] T2 on T1.role_id = T2.role_id

外部定义了一个字典类型，Query内部模型绑定的时候每次调用Function函数，Function函数中将数据添加到外部字典中，这在复杂数据处理时很有用。

static void QueryTest2()
        {
            Dapper.DefaultTypeMap.MatchNamesWithUnderscores = true;
            IDbConnection dbconnection = null;
            using (dbconnection = dbconnection.OpenConnection())
            {
                Dictionary> dic = new Dictionary>();
 
                dbconnection.QueryT(
                   @"select 1 as table1,T1.*,1 as table2,T2.* from [role] T1 left join [user] T2 on T1.role_id = T2.role_id",
                   (role, user) =>
                   {
                       if (dic.ContainsKey(role.RoleID))
                       {
                           dic[role.RoleID].Add(user);
                       }
                       else
                       {
                           dic.Add(role.RoleID, new List { user });
                       }
 
                       return true;
                   },
                   null,
                   splitOn: "table1,table2");
 
                foreach (var data in dic)
                {
                    Console.WriteLine($"role:{data.Key}");
                    foreach (var user in data.Value)
                    {
                        Console.WriteLine($"user:{user.UserID}-{user.UserName}");
                    }
                }
            }
            Console.ReadKey();
        }