思考一种好的架构（四）
作者：互联网
读写分离（CQRS）
CQRS的高大上的理论和文档一大堆，在这里就不累述了，后面的技术也是一样的，只谈我的理解，不会有很多文字描述，如果想了解更多请移步到别的文章哈。
是什么？
代码层分离数据库读写操作，搭配数据库的读写分离功能
为什么？
可以达到提高数据库执行效率，并且可以额外附带事件回溯功能
怎么做？
架构图
internal class ConnectionStrings
{
public string Key { get; set; }
public string Value { get; set; }
}
internal class ConnectionStringConfig
{
/// <summary>
/// 写库连接配置
/// </summary>
public ConnectionStrings CommandDB { get; set; }
/// <summary>
/// 读库连接配置
/// </summary>
public List<ConnectionStrings> QueryDB { get; set; }
}
配置文件 ↑
分配管理↓
/// <summary>
/// DC分配工厂
/// </summary>
public interface IDCDistributiveFactory
{
/// <summary>
/// 选择为读操作的库
/// </summary>
string SelectQuery(string QueryKey);
/// <summary>
/// 选择为写操作的库
/// </summary>
string SelectCommand();
}
public class DCDistributiveFactory : IDCDistributiveFactory
{
IServiceProvider sp;
ConnectionStringConfig config;
public DCDistributiveFactory(IServiceProvider sp)
{
this.sp = sp;
var _config = sp.GetService<IConfiguration>();
config = _config.GetSection("ConnectionStringConfig").Get<ConnectionStringConfig>();
}
/// <summary>
/// 分配为写操作
/// </summary>
public string SelectCommand()
{
//更换连接串为写库连接串
return this.config.CommandDB.Value;
}
/// <summary>
/// 分配为读操作
/// </summary>
/// <param name="QueryKey"></param>
public string SelectQuery(string QueryKey)
{
string result = string.Empty;
//更换连接串为写库连接串
if (string.IsNullOrWhiteSpace(QueryKey))
{
result = this.config.QueryDB.OrderBy(x => Guid.NewGuid()).FirstOrDefault()?.Value;
}
else
{
result = config.QueryDB.FirstOrDefault(x => x.Key.Equals(QueryKey))?.Value;
}
if (result == null)
throw new Exception($"操作库选择错误，不存在Key为{QueryKey}的读取库");
return result;
}
}
应该叫 IDCDistributive 的(*^_^*) 我懒得改了，IDCDistributiveFactory 也行，只是难免会让人联想到工厂上
它负责管理数据库连接串
CQRS的标记特性和Chloe的拦截器 ↓
特性
/// <summary>
/// 本次请求将会操作数据库
/// </summary>
public class CommandAttribute: Attribute
{
}
/// <summary>
/// 本次访问只有读取操作
/// </summary>
public class QueryAttribute:Attribute
{
/// <summary>
/// 指定的读库Sql连接字符串
/// </summary>
public string QueryKey { get; }
/// <summary>
/// 使用随机的KEY
/// </summary>
public QueryAttribute()
{
}
/// <summary>
/// 使用指定的Key
/// 若不存在则会抛出异常
/// </summary>
/// <param name="QueryKey">数据库配置文件中的Key</param>
public QueryAttribute(string QueryKey)
{
this.QueryKey = QueryKey;
}
}
拦截器：
/// <summary>
/// 写操作拦截器
/// </summary>
public class CQRSDCCommandInterceptor : IDbCommandInterceptor
{
IMediator mediator;
public CQRSDCCommandInterceptor(IMediator mediator) {
this.mediator = mediator;
}
public void NonQueryExecuted(IDbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
StringBuilder executeSql =new StringBuilder(command.CommandText);
foreach (MySql.Data.MySqlClient.MySqlParameter item in command.Parameters)
{
executeSql.Replace(item.ParameterName, item.Value.ToString());
}
mediator.Publish<DCCQRSCommandEvent>(new DCCQRSCommandEvent(executeSql.ToString(), DateTime.Now));
}
public void NonQueryExecuting(IDbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
}
public void ReaderExecuted(IDbCommand command, DbCommandInterceptionContext<IDataReader> interceptionContext)
{
}
public void ReaderExecuting(IDbCommand command, DbCommandInterceptionContext<IDataReader> interceptionContext)
{
}
public void ScalarExecuted(IDbCommand command, DbCommandInterceptionContext<object> interceptionContext)
{
}
public void ScalarExecuting(IDbCommand command, DbCommandInterceptionContext<object> interceptionContext)
{
}
}
/// <summary>
/// 读操作拦截器
/// </summary>
public class CQRSDCQueryInterceptor : IDbCommandInterceptor
{
public void NonQueryExecuted(IDbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
}
public void NonQueryExecuting(IDbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
command.Cancel();
throw new Exception("当前DC上下文不允许执行DB操作，但是却在方法中执行了DB操作,如要更改请在执行的控制器方法上标有CommandAttribute特性");
}
public void ReaderExecuted(IDbCommand command, DbCommandInterceptionContext<IDataReader> interceptionContext)
{
}
public void ReaderExecuting(IDbCommand command, DbCommandInterceptionContext<IDataReader> interceptionContext)
{
}
public void ScalarExecuted(IDbCommand command, DbCommandInterceptionContext<object> interceptionContext)
{
}
public void ScalarExecuting(IDbCommand command, DbCommandInterceptionContext<object> interceptionContext)
{
}
}
NonQueryExecuted 非查询操作执行后
NonQueryExecuting 非查询操作执行前
不知道还有人记得我上一文说的的话嘛，不要记得哈，啪啪啪~
在写操作完成后通过mediator对象发布一个事件，告诉其他服务这里有个写事件
mediator对象是EventBus服务维护的，现在还没说到那
在这有几个问题
1、我破坏了原则，动了ORM的工作（ORM服务怒目而视>_<）
2、EventBus没有被封装，暴露了mediator对象
解释：
1、CQRS引用了ORM和EventBus服务，CQRS是他们的孩子，我想就暂时这么改吧。另一种方法可以在IDCScoped中加上IDbCommandInterceptor的对象，这样的话也不算太违背服务原则吧
2、这个纯粹是我偷懒了，后续会改好的
重点↓
/// <summary>
/// 用于辨别CQRS的操作对象
/// </summary>
public class ChloeCQRSMiddleware
{
private readonly RequestDelegate _next;
public ChloeCQRSMiddleware(RequestDelegate next)
{
_next = next;
}
public Task Invoke(HttpContext httpContext)
{
ReadOrWrite(httpContext);
// Endpoint will be null if the URL didn't match an action, e.g. a 404 response
return _next(httpContext);
}
public static Endpoint GetEndpoint(HttpContext context)
{
return context.Features.Get<IEndpointFeature>()?.Endpoint;
}
/// <summary>
/// 读写判断
/// </summary>
public static void ReadOrWrite(HttpContext httpContext) {
var endpoint = GetEndpoint(httpContext);
var mediator = httpContext.RequestServices.GetService<IMediator>();
IDbCommandInterceptor dbCommand;
string connectionStr = string.Empty;
DCOperationType OperationType = DCOperationType.Query;
if (endpoint != null)
{
var command = endpoint.Metadata.GetMetadata<CommandAttribute>();
if (command != null)
{
connectionStr = httpContext.RequestServices.GetService<IDCDistributiveFactory>().SelectCommand();
OperationType = DCOperationType.Command;
dbCommand = new CQRSDCCommandInterceptor(mediator);
}
else {
var query = endpoint.Metadata.GetMetadata<QueryAttribute>();
connectionStr= httpContext.RequestServices.GetService<IDCDistributiveFactory>().SelectQuery(query?.QueryKey);
OperationType = DCOperationType.Query;
dbCommand = new CQRSDCQueryInterceptor();
}
httpContext.RequestServices.GetService<IDCScoped>().SelectOpeation(connectionStr, OperationType);
var context = httpContext.RequestServices.GetService<IDbContext>();
//添加操作拦截器
context.Session.AddInterceptor(dbCommand);
}
}
}
// Extension method used to add the middleware to the HTTP request pipeline.
public static class ChloeCQRSMiddlewareExtensions
{
public static IApplicationBuilder UseChloeCQRSMiddleware(this IApplicationBuilder builder)
{
return builder.UseMiddleware<ChloeCQRSMiddleware>();
}
}
中间件首次出现
它辨别方法上的操作特性头并操作DC选择数据库连接串和拦截器对象
其中IEndpointFeature服务这个需要AspNetCore2.2版本上
并且在CQRS中间件上加入一层app.UseEndpointRouting();
最后
public static class Startup
{
public static void ConfigureServices(IServiceCollection services)
{
services.AddSingleton<IDCDistributiveFactory, DCDistributiveFactory>();
}
public static void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseChloeCQRSMiddleware();
}
}
OK,这次我们介绍了CQRS并且实现了它，
还是有两个问题哈，以后再来改
标签：interceptionContext,架构,string,void,一种,command,思考,IDbCommand,public 来源： https://www.cnblogs.com/AnAng/p/12608826.html