1. 在appsettings.json文件中添加两个数据库连接字符串，例如：

{
  "ConnectionStrings": {
    "ProductionDatabase": "Data Source=prod_server;Initial Catalog=mydb;User ID=myuser;Password=mypassword",
    "TestDatabase": "Data Source=test_server;Initial Catalog=mydb_test;User ID=myuser;Password=mypassword"
  }
}

2. 注入IConfiguration服务到Startup.cs文件的ConfigureServices方法中：

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();
    services.AddDbContext(options =>
    {
        if (env.IsDevelopment()) // 根据环境变量选择连接字符串
        {
            options.UseSqlServer(Configuration.GetConnectionString("TestDatabase"));
        }
        else
        {
            options.UseSqlServer(Configuration.GetConnectionString("ProductionDatabase"));
        }
    });
}

3. 在需要使用数据库的类中注入MyDbContext：

public class MyController : ControllerBase
{
    private readonly MyDbContext _db;

    public MyController(MyDbContext db)
    {
        _db = db;
    }

    [HttpGet]
    public async Task Get()
    {
        var result = await _db.MyEntities.ToListAsync();
        return Ok(result);
    }
}