让Dapper在一个项目中支持多种库 / 四六文摘

dotNET跨平台

以下文章来源于桂迹，作者桂素伟

如果想在一个项目中，用DapperPlus支持多种数据库该怎么做？

在《让Dapper支持Mock》中我们定义了DapperPlus，可以基于这个类，实现两个子类：MySqlDapperPlus，MsSqlDapperPls，在这两个子类的构造中适配对应的数据库类型，从注放容器中，获取IDbConnection实例，根据实例的类型来选取配置中的对应连接字符串，这里用到的是根据数据类型来配置，也是一种约定。

MySqlDapperPlus.cs

using Microsoft.Extensions.Configuration;using System;using System.Collections.Generic;using System.Data;using System.Linq;namespace WebDemo01.Services{    public class MySqlDapperPlus : DapperPlus    {        public MySqlDapperPlus(IEnumerable<IDbConnection> connections, IConfiguration configuration)        {            var connectionStrings = configuration.GetSection("ConnectionStrings").Get<Dictionary<string, string>>();                      _connection = connections.FirstOrDefault(c => c.GetType().Name == "MySqlConnection");            _connection.ConnectionString = connectionStrings.Where(s => s.Key.ToLower().Contains("mysql")).FirstOrDefault().Value;        }    }}

MsSqlDapperPlus.cs

using Microsoft.Extensions.Configuration;using System;using System.Collections.Generic;using System.Data;using System.Linq;namespace WebDemo01.Services{    public class MsSqlDapperPlus : DapperPlus    {        public MsSqlDapperPlus(IEnumerable<IDbConnection> connections, IConfiguration configuration)        {            var connectionStrings = configuration.GetSection("ConnectionStrings").Get<Dictionary<string, string>>();                      _connection = connections.FirstOrDefault(c => c.GetType().Name == "SqlConnection");            _connection.ConnectionString = connectionStrings.Where(s => s.Key.ToLower().Contains("mssql")).FirstOrDefault().Value;        }    }}

这时，会有问题，DapperPlus没有无参构造，_connection访问级别也太低，所以要改造一下DapperPlus。

/// <summary>    /// DappePlusr类    /// </summary>    public class DapperPlus : IDapperPlus    {        protected IDbConnection _connection;        /// <summary>        /// 无参构造函数        /// </summary>        public DapperPlus()        {        }        //下面和原来的一样    }

public void ConfigureServices(IServiceCollection services){        services.AddControllers();                    services.AddScoped<IDbConnection, MySqlConnection>();        services.AddScoped<IDbConnection, SqlConnection>();        services.AddScoped<IDapperPlus, MySqlDapperPlus>();        services.AddScoped<IDapperPlus, MsSqlDapperPlus>();}

appsettings.json

"ConnectionStrings": {    "MySqlConnectionString": "server=127.0.0.1;uid=root;pwd=root;database=mysql_testdb",    "MsSqlConnectionString": "server=127.0.0.1;uid=root;pwd=root;database=mssql_testdb"  }

如果是多个库，还要读写分离该怎么实现？其实和不分离是一样的，要改造《让Dapper读写分离》中的DapperPlusWrite和DapperPlusRead两个类，分别增加无参构造函数，和把_connection改成protected，方便子类中参访问到。

然后定义三个类：MySqlDapperPlusRead和MsSqlDapperPlusRead继承DapperPlusRead；MySqlDapperPlusWrite和MsSqlDapperPlusWrite继承DapperPlusWrite。在四个类的构造函数中，按照自己数据库的类型，Read或Write类型来取配置文件中的连接字符串即可。

Startup.cs

public void ConfigureServices(IServiceCollection services){      services.AddControllers();      services.AddScoped<IDbConnection, MySqlConnection>();      services.AddScoped<IDbConnection, SqlConnection>();      services.AddScoped<IDapperPlusRead, MySqlDapperPlusRead>();      services.AddScoped<IDapperPlusRead, MsSqlDapperPlusRead>();      services.AddScoped<IDapperPlusWrite, MySqlDapperPlusWrite>();      services.AddScoped<IDapperPlusWrite, MsSqlDapperPlusWrite>();}

appsettings.json

"ConnectionStrings": {    "MySqlReadConnectionString": "server=127.0.0.1;uid=root;pwd=root;database=read_mysql_testdb",    "MySqlWriteConnectionString": "server=127.0.0.1;uid=root;pwd=root;database=write_mysql_testdb",    "MsSqlReadConnectionString": "server=127.0.0.1;uid=root;pwd=root;database=read_mssql_testdb",    "MsSqlWriteConnectionString": "server=127.0.0.1;uid=root;pwd=root;database=write_mssql_testdb"  }

最后，在业务的Service中，读有两个，按类型区分，写有两个，按类型区分，代码如下：

    public class GoodsService : IGoodsService    {        private readonly IDapperPlusWrite _mySqlDapperWrite;        private readonly IDapperPlusWrite _msSqlDapperWrite;        private readonly IDapperPlusRead _mySqlDapperRead;        private readonly IDapperPlusRead _msSqlDapperRead;        public ShopService(IEnumerable<IDapperPlusWrite> dapperWrites, IEnumerable<IDapperPlusRead> dapperReads)        {            foreach (var dapperWrite in dapperWrites)            {                switch (dapperWrite)                {                    case MySqlDapperPlusWrite mySqlDapperPlusWrite:                        _mySqlDapperWrite = mySqlDapperPlusWrite;                        break;                    case MsSqlDapperPlusWrite msSqlDapperPlusWrite:                        _msSqlDapperWrite = msSqlDapperPlusWrite;                        break;                }            }            foreach (var dapperRead in dapperReads)            {                switch (dapperRead)                {                    case MySqlDapperPlusRead mySqlDapperPlusRead:                        _mySqlDapperRead = mySqlDapperPlusRead;                        break;                    case MsSqlDapperPlusRead msSqlDapperPlusRead:                        _msSqlDapperRead = msSqlDapperPlusRead;                        break;                }            }        }    }

让Dapper在一个项目中支持多种库

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