通过DI将选定的数据库传递给DBcontext

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    // 注册数据库连接配置信息
    services.Configure<DatabaseOptions>(Configuration.GetSection("Database"));

    // 注册DBContext
    services.AddDbContext<MyDbContext>(options =>
    {
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"));
    });

    // 注册其他服务
    // ...
}

// MyDbContext.cs
public class MyDbContext : DbContext
{
    private readonly DatabaseOptions _databaseOptions;

    public MyDbContext(DbContextOptions<MyDbContext> options, IOptions<DatabaseOptions> databaseOptions)
        : base(options)
    {
        _databaseOptions = databaseOptions.Value;
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        // 使用注入的数据库连接配置信息
        optionsBuilder.UseSqlServer(_databaseOptions.ConnectionString);
    }

    // 定义实体对象的DbSet
    // ...
}

// MyService.cs
public class MyService
{
    private readonly MyDbContext _dbContext;

    public MyService(MyDbContext dbContext)
    {
        _dbContext = dbContext;
    }

    public void DoSomething()
    {
        // 使用DBContext进行数据库操作
        // ...
    }
}