asp.net core 2.2 is not using ConnectionString set in WebApp Azure config

Question

I've asp.net core 2.2 apps deployed to Azure. In the Azure portal, I added a connection string for the app, but asp.net core is not picking up that one, it is using the one in appsettings.json.

What did I do to check this? I just copied the connection string I entered in Azure to the appsettings.json file (hence replacing the development version), redeployed it and it is working fine.

Any suggestions?

public class Program
{
    public static void Main(string[] args)
    {
        WebHost
            .CreateDefaultBuilder(args)
            .UseStartup<Startup>()
            .Build()
            .Run();
    }
}

Extract from startup.cs

        public void ConfigureServices(IServiceCollection services)
        {
...
            services.AddDbContext<BattMobilityDbContext>(option => option.UseSqlServer(_configuration.GetConnectionString("BattMobilityDbConnection")));
...
}

Extract from appsettings.

  "ConnectionStrings": {
    "BattMobilityDbConnection": "Data Source=localhost\\SQLEXPRESS_JSL; initial catalog=BattMobility; integrated security=true"
  },

Screenshot from Azure

Answer 1

The solution was to add support for environmentvariables in OnConfiguring of the DbContext

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        if (_loggerFactory != null)
        {
            if (Debugger.IsAttached)
            {
                optionsBuilder.UseLoggerFactory(_loggerFactory);
            }
        }

        var configuration = new ConfigurationBuilder()
            .SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json")
             // this was the missing part
            .AddEnvironmentVariables()

            .Build();
        var connectionString = configuration.GetConnectionString("xxx");

        optionsBuilder.UseSqlServer(connectionString);
    }