Add custom section to .NET Core local.settings.json

Question

I'm writing my first Azure function (based on .NET Core 2.x), and I'm struggling to extend the app settings with my custom mapping table.

I have a file local.settings.json, and I have tried to extend it with a "custom" config section that contains a few "key/value" pairs - something like this:

{
  "IsEncrypted": false,
  "Values": {
    "FUNCTIONS_WORKER_RUNTIME": "dotnet",
    ... (standard config settings) ...
  },
  ... (more default sections, like "Host" and "ConnectionStrings")
  "MappingTable" : {
    "01" : "Value1",
    "02" : "Value2",
    "03" : "Value3",
    "else" : "Value4"
  }
}

I get the IConfiguration injected into my worker class via constructor injection, and it works just fine for the "basic" default values stored in the "Values" section:

public MyWorker(IConfiguration config)
{
    _config = config;

    string runtime = _config["FUNCTIONS_WORKER_RUNTIME"];  // works just fine

    // this also works fine - the "customSection" object is filled
    var customSection = _config.GetSection("MappingTable");

    // but now this doesn't return any values
    var children = customSection.GetChildren();

    // and trying to access like this also only returns "null"
    var mapping = customSection["01"];
}

I'm stuck here - all the blog post and articles I find seem to indicate to do just this - but in my case, this just doesn't seem to work. What am I missing here? I'm quite familiar with the full .NET framework config system - but this here is new to me and doesn't really make a whole lot of sense just yet......

I have also tried to move the entire MappingTable section to appSettings.json - but that didn't change anything, I'm still getting back only null when trying to access my custom config section's values....

Thanks!

Update: all the suggested ways of doing this work just fine with a standard ASP.NET Core 2.1 web app - but in the Azure function, it's not working. Seems like code in an Azure Function is treating configuration differently than a regular .NET Core code base ...

Why don't you use this `System.Environment.GetEnvironmentVariable($"MappingTable:01")` ? — Nilay Vishwakarma, Nov 14 '19 at 11:25
@NilayVishwakarma: tried this - but it, too, just returns "null" instead of the configured value... — marc_s, Nov 14 '19 at 12:10
@sjokkogutten: like before - just returns `null` - it's as if the .NET Core config system can't see my custom section ..... — marc_s, Nov 14 '19 at 12:16
Hm. Could you try wrapping your customsection in an AppSettings section? "AppSettings":{"MappingTable": ... etc}. And then : config["AppSettings:MappingTable:01"] — sjokkogutten, Nov 14 '19 at 12:23

sjokkogutten · Accepted Answer · 2019-11-15T07:40:58.820

4

I did something similar using .net core 3.0

local.settings.json

{
  "AppSettings":{
    "MappingTable" : {
      "01" : "Value1"       
    }
  }
}

Reading appsettings:

private void AppSettings()
{
   var config = new ConfigurationBuilder()
                        .SetBasePath(Directory.GetCurrentDirectory())
                        .AddJsonFile("local.settings.json", optional: true, reloadOnChange: true)
                        .AddEnvironmentVariables()
                        .Build();

   var 01 = config["AppSettings:MappingTable:01"];
}

In the Azure portal, you need to add this as an application setting. In your Function App -> Configuration -Application Settings -> New Application setting

Name:AppSettings:MappingTable:01
Value:Value1

edited Nov 15 '19 at 07:40

answered Nov 14 '19 at 13:27

sjokkogutten

2,005
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Looked promising - but even so: I still only get a `null` back - no matter which setting I try.... I must be missing something small, but fundamental somewhere...... – marc_s Nov 14 '19 at 15:17
**Update:** this all works just fine with a standard ASP.NET Core 2.1 web app - but in the Azure function, it's not working. Seems like code in an Azure Function is treating configuration differently that regular .NET Core code ...... – marc_s Nov 14 '19 at 19:24

score 2 · Answer 2 · answered Nov 14 '19 at 19:41

A R G H ! ! !

I knew it - such a stupid little mistake - but with rather massive consequences.....

In my startup class, I had this code (plus some more):

public class Startup : FunctionsStartup
{
    public override void Configure(IFunctionsHostBuilder builder)
    {
        builder.Services.AddHttpClient();

        var config = new ConfigurationBuilder()
            .SetBasePath(Environment.CurrentDirectory)
            .AddJsonFile("local.settings.json", optional: true, reloadOnChange: true)
            .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
            .AddEnvironmentVariables()
            .Build();
        .....
    }
}

but what was missing is this one line of code after the call to .Build() above:

        builder.Services.AddSingleton<IConfiguration>(config);

Somehow, the settings in the Values section of local.settings.json were present and accessible, but any custom config sections weren't.

Adding this one line has solved my problem - now I can easily read the MappingTable from my local.settings.json (or appsettings.json) file and use it in my code.

Is this with the .net cpre 2.1 or 3.0 – sam Jan 29 '20 at 22:34 — sam, Jan 29 '20 at 22:34

Add custom section to .NET Core local.settings.json

2 Answers2

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