How force DbContexts to read from the connection string in the right appsettings

I have multiple DbContexts in my project
I am using .Net 6 and efCore 6. I am passing connection string to the contexts like this.

public partial class MyContext : DbContext
{    
    public MyContext(DbContextOptions<MyContext> options) : base(options) { }
    public MyContext() : base() { }
}

And in program.cs

services.AddDbContext<MyContext>(options =>
{
     options.UseSqlServer(Configuration.GetSection("MyConnrctionStr").Value);     
});

The problem is I should delegate the creation of my DbContext to a third party library that does not pass connection string to the context.
So I should handle setting the right connection string in my dbContext classes themselves. Also the config should come from corresponding environment settings i.e. development, production, debug, …
So that should be something like this:

public partial class MyContext : DbContext
{    
    public MyContext(DbContextOptions<MyContext> options) : base(options) { }
    public MyContext() : base() { }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
        var string connectionStr= //Read ConnectionString From Correct appsettings.json file Regarding to Environment
            optionsBuilder.UseSqlServer(connectionStr);
        }
}

How can I achieve that?

>Solution :

You can have current environment name in the class and then read the appsetting.[currentenvironment].json with some code like this.

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(getConnectionString());
    }
    private static string getConnectionString()
    {
        var environmentName =
          Environment.GetEnvironmentVariable(
              "ASPNETCORE_ENVIRONMENT");

        var config = new ConfigurationBuilder().AddJsonFile("appsettings" + (String.IsNullOrWhiteSpace(environmentName) ? "" : "." + environmentName) + ".json", false).Build();
        return config.GetConnectionString("DefaultConnection");
    }

This way you do not need to send any thing when injecting DBContext, etc. But the name of connection string would be hard codded inside DbContext