How to set-up connection string in appsettings.json

In this article

1. Why we use appsettings.json in C#?
2. The ConfigurationBuilder object
3. Hierarchical keys
4. Create and read an appsettings.json file from class library project
5. Create and read configuration from appsettings.json C# ASP.NET WEB API project using Dependency Injection Container
6. Options design pattern

The ConfigurationBuilder object

In applications whose lifecycle and service management is provided by a .NET Generic Host the ConfigurationBuilder is part of the host object. For Console applications that don't use this approach you need to provide the ConfigurationBuilder object from a nuget package .Net is capable to read key value pair settings from various configuration sources:

• Settings files, such as appsettings.json
• Environment variables
• In-memory .NET objects
• Command-line arguments
• Azure Key Vault
• Azure App Configuration
• And more...

For each of these configuration providers you will find a different variant of the 'Microsoft.Extensions.Configuration' package. This tutorial is concentrated on Json configuration file and will work with Microsoft.Extensions.Configuration.Json

Create and read an appsettings.json file from class library project

In this guide I will show you how to create a configuration file for your project and add and read a connection string from it.

1. Create a C# class library project.
2. Create appsettings.json file at the root level of your class library project. Change the file property "Copy to Output Directory" to "Copy if newer".
   
3. Add test values inside the appsettings.json

   1{
   2  "Version": "1.0.1",
   3  "VolumeSettings": {
   4    "Max": 10,
   5    "Step": 2
   6  },
   7  "ConnectionStrings": {
   8    "DefaultConnection": "Server=localhost\SQLEXPRESS;..."
   9  }
   10}

4. Create AppConfiguration class that will read the key value pairs from appsettings.json

   1public static class AppConfiguration
   2{
   3}

5. Install nuget package Microsoft.Extensions.Configuration.Json
6. Inside AppConfiguration create one new ConfigurationBuilder object. This object knows how to load and parse json files.

   1public class AppConfiguration
   2{
   3    private IConfigurationRoot configuration;
   4
   5    public AppConfiguration()
   6    {
   7        var builder = new ConfigurationBuilder();
   8        builder.SetBasePath(Directory.GetCurrentDirectory());
   9        builder.AddJsonFile("appsettings.json", optional: true);
   10        this.configuration = builder.Build();
   11    }
   12}

7. Create methods for pulling different value structures.

   1public class AppConfiguration
   2{
   3    private IConfigurationRoot configuration;
   4
   5    public AppConfiguration()
   6    {
   7        var builder = new ConfigurationBuilder();
   8        builder.SetBasePath(Directory.GetCurrentDirectory());
   9        builder.AddJsonFile("appsettings.json", optional: true);
   10        this.configuration = builder.Build();
   11    }
   12
   13    public string? GetConnectionString(string key)
   14    {
   15        return this.configuration.GetConnectionString(key);
   16    }
   17
   18    public string? GetValue(string key)
   19    {
   20        return this.configuration[key];
   21    }
   22
   23    public T? GetObject<T>(string key)
   24        where T : class, new()
   25    {
   26        var obj = new T();
   27        this.configuration.GetSection(key).Bind(obj);
   28        return obj;
   29    }
   30}
   31

   - The GetConnectionString method reads the keys inside the “ConnectionStrings” object. The method utilises GetConnectionString from IConfigurationRoot. Another approach is to use an hierarchical object key like so:

   1public string? GetConnectionString(string key)
   2{
   3    return this.configuration["ConnectionStrings:" + key];
   4}

   - The GetValue method takes a key or a hierarchical object key and returns the configuration values.

   - With the ConfigurationBuilder object you have the ability to bind configuration sections into C# objects. To add the bind function you must install Microsoft.Extensions.Configuration.BinderAn alternative method also coming from .Binder package is this:

   1public T? GetObject<T>(string key) where T : class, new()
   2{
   3    var obj = configuration.GetRequiredSection(key).Get<T>();
   4    return obj;
   5}

And for an example on how to use these method see the following code

1public class VolumeSettings
2{
3    public int Max { get; set; }
4    public int Step { get; set; }
5}

1static void Main(string[] args)
2{
3    var config = new AppConfiguration();
4    var version = config.GetValue("Version");
5    var connectionString = config.GetConnectionString("DefaultConnection");
6    var section = config.GetObject<VolumeSettings>("VolumeSettings");
7}

Options design pattern

The options design pattern is used to encapsulate application settings by organizing them into logical groups. Each group contains settings that are closely related to one another. These groups are then parsed into C# objects and registered as entities within the dependency injection (DI) container.

1. Open Program.cs and add the following row

1builder.Services.Configure<Volume>(builder.Configuration.GetSection(Volume.SectionName));

2. The volume setting is accessible through IOptions<Volume> object

1private readonly IConfiguration configuration;
2        private readonly Volume volumeSetting;
3        
4        public HomeController(IConfiguration configuration, IOptions<Volume> volumeSettings)
5        {
6            configuration = configuration ?? throw new ArgumentNullException(nameof(configuration));
7            volumeSetting = volumeSettings.Value;
8        }

3. To get the connection string value call configuration.GetConnectionString("DefaultConnection");

1private readonly IConfiguration configuration;
2private readonly Volume volumeSetting;
3private readonly string? connectionString;
4
5public HomeController(IConfiguration configuration, IOptions<Volume> volumeSettings)
6{
7    configuration = configuration ?? throw new ArgumentNullException(nameof(configuration));
8    volumeSetting = volumeSettings.Value;
9    connectionString = configuration.GetConnectionString("DefaultConnection");
10}