在上一篇说了封装Dapper扩展方法为一个接口来支持Mock，接下来看看如何实现读写分离。

其实定义两个接口，一个用来实现读，一个用来实现写。在读的接口里只有Query的方法，在写的接口里实现Query和Execute全量(通读写的库也是支持读的，有的场景还是必须在写库里读，因为写库往读库中同步时是有时差的)。

IDapperPlusRead.cs

    /// <summary>/// DapperPlus读接口/// </summary>public interface IDapperPlusRead{/// <summary>/// 连接/// </summary>public IDbConnection Connection{get;}/// <summary>/// Executes a single-row query, returning the data typed as type./// </summary>/// <param name="type">The type to return.</param>/// <param name="sql">The SQL to execute for the query.</param>/// <param name="param">The parameters to pass, if any.</param>/// <param name="transaction">The transaction to use, if any.</param>/// <param name="buffered">Whether to buffer results in memory.</param>/// <param name="commandTimeout">The command timeout (in seconds).</param>/// <param name="commandType">The type of command to execute.</param>/// <returns>A sequence of data of the supplied type; if a basic type(int, string, etc) is queried then the data from the first column in assumed, otherwise an instance is created per row, and a direct column-name===member-name mapping is assumed(case insensitive)./// 异常:T:System.ArgumentNullException:type is null./// </returns>IEnumerable<object> Query(Type type, string sql, object param = null, IDbTransaction transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null);//这时省略n个方法}

IDapperPlusWrite.cs

    /// <summary>/// 写Dapper接口/// </summary>public interface IDapperPlusWrite{/// <summary>/// 连接/// </summary>public IDbConnection Connection{get;}/// <summary>/// Execute parameterized SQL./// </summary>/// <param name="sql">The SQL to execute for this query.</param>/// <param name="param">The parameters to use for this query.</param>/// <param name="transaction">The transaction to use for this query.</param>/// <param name="commandTimeout">Number of seconds before command execution timeout.</param>/// <param name="commandType">Is it a stored proc or a batch?</param>/// <returns>The number of rows affected.</returns>int Execute(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null);/// <summary>/// Executes a single-row query, returning the data typed as type./// </summary>/// <param name="type">The type to return.</param>/// <param name="sql">The SQL to execute for the query.</param>/// <param name="param">The parameters to pass, if any.</param>/// <param name="transaction">The transaction to use, if any.</param>/// <param name="buffered">Whether to buffer results in memory.</param>/// <param name="commandTimeout">The command timeout (in seconds).</param>/// <param name="commandType">The type of command to execute.</param>/// <returns>A sequence of data of the supplied type; if a basic type(int, string, etc) is queried then the data from the first column in assumed, otherwise an instance is created per row, and a direct column-name===member-name mapping is assumed(case insensitive)./// 异常:T:System.ArgumentNullException:type is null./// </returns>IEnumerable<object> Query(Type type, string sql, object param = null, IDbTransaction transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null);//这时省略n个方法}

按照读写接口实现各自的类，这里就要在两个类的构造里取出各自己的连接字符串(读写库的实例或库名有所区别)，这里用了个约定，就是在配置里，连接字符串的名称有read或write字样，通过这个约定来分别取读写连接字符串。

DapperPlusRead.cs

   /// <summary>/// DapperPlus读实现类/// </summary>public class DapperPlusRead : IDapperPlusRead{protected IDbConnection _connection;/// <summary>/// 构造/// </summary>/// <param name="connection">连接</param>/// <param name="configuration">配置</param>public DapperPlusRead(IDbConnection connection, IConfiguration configuration){            var connectionStrings = configuration.GetSection("ConnectionStrings").Get<Dictionary<string, string>>();_connection = connection;_connection.ConnectionString = connectionStrings.Where(s => s.Key.ToLower().Contains("read")).FirstOrDefault().Value;  }/// <summary>/// 连接/// </summary>public IDbConnection Connection{get{return _connection;}}/// <summary>/// Executes a single-row query, returning the data typed as type./// </summary>/// <param name="type">The type to return.</param>/// <param name="sql">The SQL to execute for the query.</param>/// <param name="param">The parameters to pass, if any.</param>/// <param name="transaction">The transaction to use, if any.</param>/// <param name="buffered">Whether to buffer results in memory.</param>/// <param name="commandTimeout">The command timeout (in seconds).</param>/// <param name="commandType">The type of command to execute.</param>/// <returns>A sequence of data of the supplied type; if a basic type(int, string, etc) is queried then the data from the first column in assumed, otherwise an instance is created per row, and a direct column-name===member-name mapping is assumed(case insensitive)./// 异常:T:System.ArgumentNullException:type is null./// </returns>public IEnumerable<object> Query(Type type, string sql, object param = null, IDbTransaction transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null){return _connection.Query(type, sql, param, transaction, buffered, commandTimeout, commandType);}//这时省略n个方法}

DapperPlusWrite.cs

    /// <summary>/// 写Dapper类/// </summary>public class DapperPlusWrite : IDapperPlusWrite{private readonly IDbConnection _connection;/// <summary>/// 构造/// </summary>/// <param name="connection">连接</param>/// <param name="configuration">配置</param>public DapperPlusWrite(IDbConnection connection, IConfiguration configuration){var connectionStrings = configuration.GetSection("ConnectionStrings").Get<Dictionary<string, string>>();_connection = connection;_connection.ConnectionString = connectionStrings.Where(s => s.Key.ToLower().Contains("write")).FirstOrDefault().Value;}/// <summary>/// 连接/// </summary>public IDbConnection Connection{get{return _connection;}}/// <summary>/// Execute parameterized SQL./// </summary>/// <param name="sql">The SQL to execute for this query.</param>/// <param name="param">The parameters to use for this query.</param>/// <param name="transaction">The transaction to use for this query.</param>/// <param name="commandTimeout">Number of seconds before command execution timeout.</param>/// <param name="commandType">Is it a stored proc or a batch?</param>/// <returns>The number of rows affected.</returns>public int Execute(string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null){return _connection.Execute(sql, param, transaction, commandTimeout, commandType);}/// <summary>/// Executes a single-row query, returning the data typed as type./// </summary>/// <param name="type">The type to return.</param>/// <param name="sql">The SQL to execute for the query.</param>/// <param name="param">The parameters to pass, if any.</param>/// <param name="transaction">The transaction to use, if any.</param>/// <param name="buffered">Whether to buffer results in memory.</param>/// <param name="commandTimeout">The command timeout (in seconds).</param>/// <param name="commandType">The type of command to execute.</param>/// <returns>A sequence of data of the supplied type; if a basic type(int, string, etc) is queried then the data from the first column in assumed, otherwise an instance is created per row, and a direct column-name===member-name mapping is assumed(case insensitive)./// 异常:T:System.ArgumentNullException:type is null./// </returns>public IEnumerable<object> Query(Type type, string sql, object param = null, IDbTransaction transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null){return _connection.Query(type, sql, param, transaction, buffered, commandTimeout, commandType);}//这时省略n个方法}

剩下的就是注入了，使用读时用IDapperPlusRead就可以，写就用IDapperPlusWrite。

public void ConfigureServices(IServiceCollection services)
{services.AddControllers();services.AddScoped<IDbConnection, MySqlConnection>();services.AddScoped<IDapperPlusRead, DapperPlusRead>();services.AddScoped<IDapperPlusWrite, DapperPlusWrite>();
}

appsettings.json

  "ConnectionStrings": {"ReadConnectionString": "server=127.0.0.1;uid=root;pwd=root;database=read_mysql_testdb","WriteConnectionString": "server=127.0.0.1;uid=root;pwd=root;database=write_mysql_testdb"}