How to reference another value within the same appsettings.json file?

Question

I need database connection string in two places in appsettings.json.

Is it possible to introduce common variable or json-path related references into json file to avoid potencial problems?

It would be lovely to have it without touching c# code.

{
...
  "ConnectionStrings": {
    "Default": "Host=localhost;Database=db;Port=5432;Username=postgres;Password=postgres"
  },
  "Nlog": {
    "targets": {
      "database": {
        "type": "Database",
        "dbProvider": "Npgsql.NpgsqlConnection, Npgsql",
        "connectionString": "Host=localhost;Database=db;Port=5432;Username=postgres;Password=postgres",
...
      }
    }
...
}

Answer 1

NLog has the ability to lookup values in the appsettings.json. You can do it like this with ${configsetting}:

{
...
  "ConnectionStrings": {
    "Default": "Host=localhost;Database=db;Port=5432;Username=postgres;Password=postgres"
  },
  "Nlog": {
    "targets": {
      "database": {
        "type": "Database",
        "dbProvider": "Npgsql.NpgsqlConnection, Npgsql",
        "connectionString": "${configsetting:item=ConnectionStrings.Default}",
...
      }
    }
...
}

See also https://github.com/NLog/NLog/wiki/ConfigSetting-Layout-Renderer

Answer 2

I've created a nuget package exactly for this! Check it out here: https://www.nuget.org/packages/TemplateFormattedConfiguration/

In your example you should do this:

{
...
    "ConnectionStrings": {
"Default": "Host=localhost;Database=db;Port=5432;Username=postgres;Password=postgres"
  },
  "Nlog": {
    "targets": {
      "database": {
        "type": "Database",
        "dbProvider": "Npgsql.NpgsqlConnection, Npgsql",
        "connectionString": "{ConnectionStrings:Default}",
...
      }
    }
...
}

And in your Startup.cs (or Program.cs) you'll add this:

        configuration.EnableTemplatedConfiguration();