分库¶

当我们发现单个数据库的性能无法满足需求时，我们可以考虑将数据分散到多个数据库中，

关于事务¶

由于分库会产生跨数据库事务的问题，尤其是集成事件的本地消息需要共享当前上下文的事务，因此我们实现了在同一个命令执行范围内，确保集成事件的发布记录保存到与业务数据相同的数据源中。

因此会有如下注意事项：

同一个命令中只操作同一分库的数据时，能够确保集成事件的发布记录保存到与业务数据相同的数据源中。
同一个请求上下文涉及不同分库时，sharding-core 会为每个对应数据源开启各自的事务。

更多关于分库事务的说明，请参考：https://xuejmnet.github.io/sharding-core-doc/adv/transaction/

配置分库¶

添加包NetCorePal.Extensions.ShardingCore引用：

dotnet add package NetCorePal.Extensions.ShardingCore

或者 PackageReference

<PackageReference Include="NetCorePal.Extensions.ShardingCore" />

为你的 DbContext 类型添加 IShardingCore 接口

public partial class ApplicationDbContext : AppDbContextBase, IShardingCore
{
    //Your Code
}

创建ApplicationDbContextCreator

public class ApplicationDbContextCreator(IShardingProvider provider)
    : IDbContextCreator
{
    public DbContext CreateDbContext(DbContext shellDbContext, ShardingDbContextOptions shardingDbContextOptions)
    {
        var outDbContext = (ApplicationDbContext)shellDbContext;
        var dbContext = new ApplicationDbContext(
            (DbContextOptions<ApplicationDbContext>)shardingDbContextOptions.DbContextOptions, outDbContext.Mediator);
        if (dbContext is IShardingTableDbContext shardingTableDbContext)
        {
            shardingTableDbContext.RouteTail = shardingDbContextOptions.RouteTail;
        }

        _ = dbContext.Model;
        return dbContext;
    }

    public DbContext GetShellDbContext(IShardingProvider shardingProvider)
    {
        return shardingProvider.GetRequiredService<ApplicationDbContext>();
    }
}

移除 AddDbContext 注册方式

builder.Services.AddDbContext<ApplicationDbContext>(options =>
    {
        options.UseMySql(builder.Configuration.GetConnectionString("Mysql"),
            new MySqlServerVersion(new Version(8, 0, 34)),
            b => { b.MigrationsAssembly(typeof(Program).Assembly.FullName); });
    });

添加包 NetCorePal.Extensions.DistributedTransactions.CAP.MySql 以支持CAP的发布消息分库：

dotnet add package NetCorePal.Extensions.DistributedTransactions.CAP.MySql

为 ApplicationDbContext 添加 IMySqlCapDataStorage 接口:

public partial class ApplicationDbContext : AppDbContextBase, 
IShardingCore, IMySqlCapDataStorage
{
//Your Code
}

修改AddCap代码，配置UseNetCorePalStorage

services.AddCap(op =>
{
   op.UseNetCorePalStorage<ShardingDatabaseDbContext>(); //配置使用UseNetCorePalStorage 以支持分库
   op.UseRabbitMQ(p =>
   {
      p.HostName = _rabbitMqContainer.Hostname;
      p.UserName = "guest";
      p.Password = "guest";
      p.Port = _rabbitMqContainer.GetMappedPublicPort(5672);
      p.VirtualHost = "/";
   }); 
});

MS SqlServer 以及 PostgreSql 也可以使用对应的包来支持

dotnet add package NetCorePal.Extensions.DistributedTransactions.CAP.SqlServer
dotnet add package NetCorePal.Extensions.DistributedTransactions.CAP.PostgreSql

配置MediatR添加AddShardingBehavior,注意需要添加在AddUnitOfWorkBehaviors之前:

services.AddMediatR(cfg =>
                 cfg.RegisterServicesFromAssembly(typeof(ShardingDatabaseDbContextTests).Assembly)
                     .AddShardingBehavior()    //添加在`AddUnitOfWorkBehaviors`之前
                     .AddUnitOfWorkBehaviors());

为分库的实体添加分库路由配置，分库需要实现基类NetCorePalVirtualDataSourceRoute:

public class OrderVirtualDataSourceRoute(IOptions<NetCorePalShardingCoreOptions> options)
 : NetCorePalVirtualDataSourceRoute<Order,
     string>(options)
{
    public override void Configure(EntityMetadataDataSourceBuilder<Order> builder)
    {
        builder.ShardingProperty(o => o.Area); //返回分库字段
    }

    protected override string GetDataSourceName(object? shardingKey)
    {
        return shardingKey == null ? string.Empty : shardingKey.ToString()!; //实现自定义分库逻辑
    }
}

配置ShardingCore:

services.AddShardingDbContext<ShardingDatabaseDbContext>()
                 .UseNetCorePal(op =>  //配置分库名称，需要UseConfig中配置的名称保持一致
                 {
                     op.AllDataSourceNames = ["Db0", "Db1"];
                     op.DefaultDataSourceName = "Db0";
                 })
                 .UseRouteConfig(op =>
                 {
                     op.AddCapShardingDataSourceRoute();  //添加默认的PubishedMessage分库路由
                     op.AddShardingDataSourceRoute<OrderVirtualDataSourceRoute>();  //添加实体分库路由
                 }).UseConfig(op =>
                 {
                     op.ThrowIfQueryRouteNotMatch = true;
                     op.UseShardingQuery((conStr, builder) =>
                     {
                         builder.UseMySql(conStr,
                             new MySqlServerVersion(new Version(8, 0, 34)));
                     });
                     op.UseShardingTransaction((conStr, builder) =>
                     {
                         builder.UseMySql(conStr,
                             new MySqlServerVersion(new Version(8, 0, 34)));
                     });
                     op.AddDefaultDataSource("Db0", _mySqlContainer0.GetConnectionString());
                     op.AddExtraDataSource(_ => new Dictionary<string, string>
                     {
                         { "Db1", _mySqlContainer1.GetConnectionString() }
                     });
                 })
                 .ReplaceService<IDbContextCreator, ShardingDatabaseDbContextCreator>()
                 .AddShardingCore();

高级¶

更多分库配置请参考官方文档：https://xuejmnet.github.io/sharding-core-doc/sharding-data-source/init/