How can I read an object tree using Configuration GetRequiredSection()?

How can I read a .NET Core configuration section having nested properties?

This is my configuration (excerpt):

{
  "SMTP":
  {
    "Name": "...",
    "UserName": "...",
    "Password": "...",
    "HostName": "...",
    "Port": "587",
    "Security": "STARTTLS",
    "OAuth2":
    {
      "ClientId": "",
      "ClientSecret": "",
      "Scopes":
      [
      ]
    }
  }
}

And these are the record types I'm using to read above configuration section:

public record OAuth2Credentials(string ClientId, string ClientSecret, string[] Scopes);

public record SmtpConfiguration(string Name, string UserName, string Password, string HostName, int Port, string Security, OAuth2Credentials OAuth2);

Then, when I try to read above configuration using the following line:

SmtpConfiguration smtpConfig =
   Program.Configuration!
  .GetRequiredSection("SMTP")
  .Get<SmtpConfiguration>()!;

… I get the following error:

System.InvalidOperationException: Cannot create instance of type
'WebApi.SendEMail.SmtpConfiguration' because parameter 'OAuth2' has
no matching config. Each parameter in the constructor that does not
have a default value must have a corresponding config entry.

.

How can I read an object tree using Configuration GetRequiredSection()?

Edit

My Solution Chosen From Given Answers:

using System;

public record OAuth2Credentials(string ClientId, string ClientSecret)
{
  public string[] Scopes = Array.Empty<string>();
}

public record SmtpConfiguration(string Name, string UserName, string Password, string HostName, int Port, string Security)
{
  public OAuth2Credentials OAuth2 = new OAuth2Credentials("", "");
}


try
{
  smtpConfig = Program.Configuration!.GetRequiredSection("SMTP").Get<SmtpConfiguration>()!;
  smtpConfig.OAuth2 = Program.Configuration!.GetRequiredSection("SMTP:OAuth2").Get<OAuth2Credentials>()!;
  smtpConfig.OAuth2.Scopes = Program.Configuration!.GetRequiredSection("SMTP:OAuth2:Scopes").Get<string[]>()!;
}
catch (InvalidOperationException ex) { return TypedResults.BadRequest($"Invalid SMTP configuration: {ex.Message}"); }

This solution seems most type-safe to me.

Because you are using record you have to give each parameter a default value in order to use it like this,

below code is the full example of usage:

public record SmtpConfiguration(string Name, string UserName, string Password, string HostName, int Port, string Security, OAuth2Credentials OAuth2);
public record OAuth2Credentials(string ClientId, string ClientSecret, string[] Scopes);

SmtpConfiguration smtpConfig = new SmtpConfiguration("", "", "", "", 0, "", new OAuth2Credentials("", "", new string[] { }));

Configuration.GetSection("SMTP").Bind(smtpConfig);

Here is the result

I hope it helps

> How can I read a .NET Core configuration section having nested
> properties?

Below is a work demo, you can refer to it, hope it can help.

1.Put configuration into SmtpConfiguration.json.

2. Add below code to your Program.cs (asp.net core 6.0+):

    var configuration = new ConfigurationBuilder()
        .AddJsonFile("SmtpConfiguration.json")
        .Build();
    var Port = configuration.GetValue<int>("SMTP:Port");
    IConfigurationSection myArraySection = configuration.GetSection("SMTP:OAuth2:Scopes");
    var itemArray = myArraySection.AsEnumerable();

Result(For test, I change the Scopes to "Scopes": [
"str1",
"str2",
"str3"
]):

You can read Configuration in ASP.NET Core and Options pattern in ASP.NET Core to know more.