EntityFrameworkCore + MySQL 主从复制应用读写分离

前置条件

　　MySQL 主从复制：https://www.cnblogs.com/fallTakeMan/p/14038888.html

环境说明

　　本机开发环境：Win10，VS2019，.NetCoreSDK 3.1

　　MySQL 服务器：192.168.187.66:3306（写），192.168.187.66:3307（读）

项目结构

　　一个 webapi 项目，两个 dotnetcore 类库项目，ftm.EFcore 引用 ftm.Entity，ftm.api 引用 ftm.EFcore。

项目说明

　　ftm.EFcore 项目引用 nuget 包 Microsoft.EntityFrameworkCore（3.1.1），MySql.Data.EntityFrameworkCore（8.0.22）。

　　创建三个文件 AppDbContext，IDbContextFactory，DbContextFactory。

using ftm.Entity;
using Microsoft.EntityFrameworkCore;


namespace ftm.EFcore
{
    public class AppDbContext : DbContext
    {
        private string connString = string.Empty;
        /// <summary>
        /// 传入数据库链接字符串构造 AppDbContext
        /// </summary>
        /// <param name="conn">数据库链接字符串</param>
        public AppDbContext(string conn)
        {
            connString = conn;
        }

        public DbSet<User> User { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder options)
        {
            options.UseMySQL(connString);
        }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            builder.Entity<User>().HasKey(x => x.Id);
        }
    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace ftm.EFcore
{
    /// <summary>
    /// DbContext 工厂
    /// </summary>
    public interface IDbContextFactory
    {
        public AppDbContext CreateDbContext(DbContextType contextType);
    }
    /// <summary>
    /// 读写类型
    /// </summary>
    public enum DbContextType
    {
        Write,
        Read
    }
}

using Microsoft.Extensions.Configuration;
using System;
using System.Collections.Generic;
using System.Text;

namespace ftm.EFcore
{
    /// <summary>
    /// DbContext 工厂
    /// </summary>
    public class DbContextFactory : IDbContextFactory
    {
        private IConfiguration _configuration;
        private string[] _readConn;
        /// <summary>
        /// 传入配置接口构造 DbContextFactory
        /// </summary>
        /// <param name="configuration">配置项接口</param>
        public DbContextFactory(IConfiguration configuration)
        {
            _configuration = configuration;
            _readConn = _configuration["ConnectionString:ReadConnStr"].Split(",");
        }
        public AppDbContext CreateDbContext(DbContextType contextType)
        {
            string connStr = string.Empty;
            switch (contextType)
            {
                case DbContextType.Write:
                    connStr = _configuration["ConnectionString:WriteConnStr"];
                    break;
                case DbContextType.Read:
                    connStr = GetReadConn();
                    break;

            }
            return new AppDbContext(connStr);
        }
        /// <summary>
        /// 获取读库链接字符串
        /// </summary>
        /// <remarks>
        /// TODO:根据不同策略获取链接字符串
        /// </remarks>
        /// <returns>读库链接字符串</returns>
        private string GetReadConn()
        {
            // 读库策略

            int index = new Random().Next(0, _readConn.Length - 1);
            return _readConn[index];
        }
    }
}

　　ftm.api 项目配置数据库链接字符串。

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*",
  "ConnectionString": {
    "WriteConnStr": "Server=192.168.187.66;port=3306;database=test_db;uid=root;pwd=root",
    "ReadConnStr": "Server=192.168.187.66;port=3307;database=test_db;uid=root;pwd=root"
  }
}

　　Startup 中注入 DbContextFactory。

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
   services.AddScoped<IDbContextFactory, DbContextFactory>();

   services.AddControllers();
}

　　在 ftm.api 项目中应用读写分离。

　　查看 MySQL 主库和从库，User 表和数据同步。