如今，我們操作資料庫一般用ORM框架

現在用.NET Core + EFCore +SqlServer實現資料讀寫分離

介紹

為什麼要讀寫分離？

降低資料庫伺服器的壓力

如何實現讀寫分離？

1.一個主庫多個從庫

2.配置主庫複製資料到從庫

為什麼一個主庫多個從庫？

一般查詢多於增刪改，這就是我們常說的二八原則，20%操作是增刪改，80%操作是查詢

是否有缺點？

有延遲

如何解決延遲問題？

比較及時性的資料還是通過主庫查詢

具體如何實現？

通過釋出伺服器，主庫釋出，而從庫訂閱，從而實現主從庫

實現

SqlServer實現

使用SqlServer 2019，新建一個主庫，建立表，再通過本地釋出建立釋出，

然後通過本地訂閱訂閱主庫，建立兩個從庫

.NET Core MVC專案實現

專案結構

首先，在appsettings.json配置資料庫連線字串

1. {
2. "Logging": {
3. "LogLevel": {
4. "Default": "Information",
5. "Microsoft": "Warning",
6. "Microsoft.Hosting.Lifetime": "Information"
7. }
8. },
9. "AllowedHosts": "*",
10. "ConnectionStrings": {
11. "EFCoreTestToRead": "Server=GREAMBWANG-DC\\MSSQLSERVER2019;Database=EFCoreTestToRead01;Trusted_Connection=True;,Server=GREAMBWANG-DC\\MSSQLSERVER2019;Database=EFCoreTestToRead02;Trusted_Connection=True;",
12. "EFCoreTestToWrite": "Server=GREAMBWANG-DC\\MSSQLSERVER2019;Database=EFCoreTest;Trusted_Connection=True;"
13. }
14. }

Models層實現

建立模型

1. public class UserInfo
2. {
3. [Key]
4. public int Id { get; set; }
5. public string Name { get; set; }
6. public int Age { get; set; }
8. }

建立上下文

1. public class EFCoreContext : DbContext
2. {
3. public EFCoreContext(string connectionString)
4. {
5. ConnectionString = connectionString;
7. //建立資料庫
8. //Database.EnsureCreated();
9. }
11. private string ConnectionString { get; }
13. public DbSet<UserInfo> UserInfo { get; set; }
15. /// <summary>
16. /// 配置連線資料庫
17. /// </summary>
18. /// <param name="optionsBuilder"></param>
19. protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
20. {
21. //base.OnConfiguring(optionsBuilder);
22. optionsBuilder.UseSqlServer(ConnectionString);
25. }
27. protected override void OnModelCreating(ModelBuilder modelBuilder)
28. {
29. //base.OnModelCreating(modelBuilder);
31. //初始化資料
32. modelBuilder.Entity<UserInfo>().HasData(new List<UserInfo>()
33. {
34. new UserInfo() { Id = 1, Name = "哈哈", Age = 17 },
35. new UserInfo() { Id = 2, Name = "呵呵", Age = 18 },
36. new UserInfo() { Id = 3, Name = "嘻嘻", Age = 19 }
37. });
38. }
39. }

建立上下文工廠

讀寫列舉

1. public enum WriteAndReadEnum
2. {
3. Write,
4. Read
5. }

介面

1. public interface IDbContextFactory
2. {
3. EFCoreContext CreateContext(WriteAndReadEnum writeAndRead);
4. }

實現

在實現資料查詢上，可以使用不同的策略，一般有隨機策略，權重策略，輪詢策略

隨機策略：隨機選擇一個從庫進行查詢

權重策略：根據權重比例選擇從庫查詢

輪詢策略：根據順序選擇從庫查詢

1. public class DbContextFactory : IDbContextFactory
2. {
3. private IConfiguration Configuration { get; }
4. private string[] ReadConnectionStrings;
5. public DbContextFactory(IConfiguration configuration)
6. {
7. Configuration = configuration;
8. ReadConnectionStrings = Configuration.GetConnectionString("EFCoreTestToRead").Split(",");
9. }
11. public EFCoreContext CreateContext(WriteAndReadEnum writeAndRead)
12. {
13. string connectionString = string.Empty;
14. switch (writeAndRead)
15. {
16. case WriteAndReadEnum.Write:
17. connectionString = Configuration.GetConnectionString("EFCoreTestToWrite");
18. break;
19. case WriteAndReadEnum.Read:
20. connectionString = GetReadConnectionString();
21. break;
22. default:
23. break;
24. }
25. return new EFCoreContext(connectionString);
26. }
28. private string GetReadConnectionString()
29. {
30. /*
31. * 隨機策略
32. * 權重策略
33. * 輪詢策略
34. */
36. //隨機策略
37. string connectionString = ReadConnectionStrings[new Random().Next(0, ReadConnectionStrings.Length)];
39. return connectionString;
40. }
41. }

Models層完成

在Web層中

在Startup的ConfigureServices方法新增依賴注入

services.AddScoped<IDbContextFactory, DbContextFactory>();

操作

1. public class HomeController : Controller
2. {
3. private readonly ILogger<HomeController> _logger;
5. public IDbContextFactory DbContextFactory { get; }
7. public HomeController(ILogger<HomeController> logger,IDbContextFactory dbContextFactory)
8. {
9. _logger = logger;
10. DbContextFactory = dbContextFactory;
11. }
13. public IActionResult Index()
14. {
15. //寫入操作
16. EFCoreContext writeContext = DbContextFactory.CreateContext(WriteAndReadEnum.Write);
17. writeContext.UserInfo.Add(new UserInfo() { Name = "AA", Age = 20 });
18. writeContext.SaveChanges();
20. //查詢操作
21. EFCoreContext readContext = DbContextFactory.CreateContext(WriteAndReadEnum.Read);
22. UserInfo userInfo = readContext.UserInfo.OrderByDescending(u => u.Id).FirstOrDefault();
24. return View();
25. }
26. }