如何基于ClusterName从依赖注入中获取指定的IDbFactory实例？

在依赖注入（DI）容器中注册了两个对应不同DatabaseClient的IDbFactory单例服务，代码如下：

_ = services.AddSingleton<IDbFactory>(x =>
{
    var dbFactory = new DbFactory(x.GetRequiredService<IConfiguration>(), x.GetRequiredService<IKeyVaultManager>(), "ClusterName1");
    return dbFactory;
});

_ = services.AddSingleton<IDbFactory>(x =>
{
    var dbFactory = new DbFactory(x.GetRequiredService<IConfiguration>(), x.GetRequiredService<IKeyVaultManager>(), "ClusterName2");
    return dbFactory;
});

现在希望在TestRepository的构造函数中，以ClusterName作为键获取对应的IDbFactory实例，请问该如何实现？

public class TestRepository : DbRepository<SomeEntity>, ITestRepository
{
    public TestRepository(ILogger<DbRepository<SomeEntity>> logger, IDbFactory clientFactory)
        : base(logger, clientFactory)
    {
    }
}

方法1：使用.NET 6+的键服务（Keyed Services） #

如果项目基于.NET 6及以上版本，框架内置的键服务是最简洁的实现方式：

1. 注册时指定键
   替换原注册代码，用AddKeyedSingleton将ClusterName作为标识键：

_ = services.AddKeyedSingleton<IDbFactory>("ClusterName1", x =>
{
    var dbFactory = new DbFactory(x.GetRequiredService<IConfiguration>(), x.GetRequiredService<IKeyVaultManager>(), "ClusterName1");
    return dbFactory;
});

_ = services.AddKeyedSingleton<IDbFactory>("ClusterName2", x =>
{
    var dbFactory = new DbFactory(x.GetRequiredService<IConfiguration>(), x.GetRequiredService<IKeyVaultManager>(), "ClusterName2");
    return dbFactory;
});

2. 构造函数中按键注入
   修改TestRepository的构造函数，通过[FromKeyedServices]特性指定要获取的实例键：

public class TestRepository : DbRepository<SomeEntity>, ITestRepository
{
    public TestRepository(ILogger<DbRepository<SomeEntity>> logger, 
                          [FromKeyedServices("ClusterName1")] IDbFactory clientFactory)
        : base(logger, clientFactory)
    {
    }
}

如果需要动态指定键（比如从配置读取），可以注入IServiceProvider，调用GetRequiredKeyedService<IDbFactory>("目标ClusterName")获取对应实例。

方法2：自定义工厂类管理实例 #

若项目版本不支持键服务，可自行封装解析类来管理不同IDbFactory实例：

1. 创建解析接口与实现类

public interface IDbFactoryResolver
{
    IDbFactory GetDbFactory(string clusterName);
}

public class DbFactoryResolver : IDbFactoryResolver
{
    private readonly IEnumerable<IDbFactory> _dbFactories;

    public DbFactoryResolver(IEnumerable<IDbFactory> dbFactories)
    {
        _dbFactories = dbFactories;
    }

    public IDbFactory GetDbFactory(string clusterName)
    {
        var factory = _dbFactories.FirstOrDefault(f => f.ClusterName == clusterName);
        if (factory == null)
        {
            throw new ArgumentException($"未找到对应集群 {clusterName} 的IDbFactory实例");
        }
        return factory;
    }
}

注意：需要确保DbFactory类暴露ClusterName属性，用于实例筛选

2. 注册解析类与所有IDbFactory

// 先注册两个IDbFactory实例
_ = services.AddSingleton<IDbFactory>(x =>
{
    var dbFactory = new DbFactory(x.GetRequiredService<IConfiguration>(), x.GetRequiredService<IKeyVaultManager>(), "ClusterName1");
    return dbFactory;
});

_ = services.AddSingleton<IDbFactory>(x =>
{
    var dbFactory = new DbFactory(x.GetRequiredService<IConfiguration>(), x.GetRequiredService<IKeyVaultManager>(), "ClusterName2");
    return dbFactory;
});

// 注册解析类
_ = services.AddSingleton<IDbFactoryResolver, DbFactoryResolver>();

3. 在Repository中使用解析类

public class TestRepository : DbRepository<SomeEntity>, ITestRepository
{
    public TestRepository(ILogger<DbRepository<SomeEntity>> logger, 
                          IDbFactoryResolver factoryResolver)
        : base(logger, factoryResolver.GetDbFactory("ClusterName1"))
    {
    }
}

方法3：直接注入集合后筛选 #

简单场景下，可直接注入所有IDbFactory实例，在构造函数中筛选目标实例：

public class TestRepository : DbRepository<SomeEntity>, ITestRepository
{
    public TestRepository(ILogger<DbRepository<SomeEntity>> logger, 
                          IEnumerable<IDbFactory> dbFactories)
        : base(logger, dbFactories.First(f => f.ClusterName == "ClusterName1"))
    {
    }
}

这种方式适合单次使用，但若多个地方需要筛选，会产生重复代码，不如自定义解析类优雅。

内容的提问来源于stack exchange，提问作者Juhi Shrivastava