在上一篇说了封闭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
}
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"
}
想要更快更方便的了解相关知识，可以关注微信公众号