.NET Core get connection string from appsettings.json

Question

I develop a simple web app and, in the future, I want to do it as multi-tenancy.

So I want to write the connection string straight into OnConfiguring method:

public class ApplicationContext : DbContext
{
    public DbSet<User> Users { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("connection string from appsettings.json");
        base.OnConfiguring(optionsBuilder);
    }
}

Startup class:

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<ApplicationContext>();
    services.AddMvc();
}

How can I extract connection string from appsettings.json into ApplicationContext class?

I wouldn't like to create any constructors for ApplicationContext class.

Answer 1

Let's imagine that you have .NET Core application and your appsettings.json file looks like this:

{
  "Logging": {
    "IncludeScopes": false,
    "LogLevel": {
      "Default": "Debug",
      "System": "Information",
      "Microsoft": "Information"
    }
  },
  "Production": {
    "SqliteConnectionString": "Filename=./MyDatabase.sqlite"
  }
}

You can get SqliteConnectionString value from Startup.cs like this:

public void ConfigureServices(IServiceCollection services)
{
    var connection = Configuration["Production:SqliteConnectionString"];

    services.AddDbContext<MyContext>(options =>
        options.UseSqlite(connection)
    );
    ....
 }

And then in your DBContext you should add constructor that accepts DbContextOptions :

public class MyContext : DbContext
{
    public MyContext (DbContextOptions<MyContext> options) : base(options)
    { }

    ...
}

Answer 2

So I want to write the connection string straight into OnConfiguring method:

How can I extract connection string from appsettings.json into ApplicationContext class?

I wouldn't like to create any constructors for ApplicationContext class.

You could use Options Pattern via IOptions but the easiest way is using DI in ApplicationContext constructor ;)

Follow below articles, please:

• Example of using IOptions ,
• Using Options and configuration objects ,
• IOptions Interface ,

Answer 3

.NET Core 2.0

Add this class:

// Requires NuGet package Microsoft.Extensions.Configuration.Json

using Microsoft.Extensions.Configuration;
using System.IO;

namespace RutarBackgroundServices.AppsettingsJson
{
    public static class AppSettingsJson
    {
        public static string ApplicationExeDirectory()
        {
            var location = System.Reflection.Assembly.GetExecutingAssembly().Location;
            var appRoot = Path.GetDirectoryName(location);

            return appRoot;
        }

        public static IConfigurationRoot GetAppSettings()
        {
            string applicationExeDirectory = ApplicationExeDirectory();

            var builder = new ConfigurationBuilder()
            .SetBasePath(applicationExeDirectory)
            .AddJsonFile("appsettings.json");

            return builder.Build();
        }


    }
}

Get the value for the key "MssqlConnectionString" from the "appsettings.json" file:

var appSettingsJson = AppSettingsJson.GetAppSettings();
var connectionString = appSettingsJson["MssqlConnectionString"];

Create the file "appsettings.json" in the root directory of your project:

{
  "MssqlConnectionString": "Server=yourip; Database=yourdbname; User Id=yourusername; Password=yourpassword; Pooling=true;",
  "Db2ConnectionString": "Database=yourdbname;UserID=yourusername;Password=yourpassword;Server=yourip:yourport",
  "SomeOtherKey": "SomeOtherValue"
}

Answer 4

You can use the factory pattern to resolve your DbContext .

public interface ITenantDbContextFactory
{
    ApplicationContext Create(string tenantId);
}

public class TenantDbContextFactory()
{
    private ApplicationContext context;

    public TenantDbContextFactory()
    {
    }

    public ApplicationContext Create(string tenantId) 
    {
        if(this.context==null) 
        {
            var connectionString = GetConnectionForTenant(tenantId);
            var dbContextBuilder = new DbContextOptionsBuilder();
            dbContextBuilder.UseSqlServer(connectionString);

            this.context = new ApplicationContext(dbContextBuilder);
        }

        return this.context;
    }
}

In Startup:

services.AddDbContext<ApplicationContext>();
services.AddScoped<ITenantDbContextFactory, TenantDbContextFactory>();

Your service or controller:

public class HomeController 
{
    private readonly ITenantDbContextFactory dbFactory;
    public HomeControler(ITenantDbContextFactory tenantDbContextFactory)
    {
        this.dbFactory = tenantDbContextFactory;
    }

    public void Action()
    {
        var dbContext = this.dbFactory.Create("tenantA");
        // use your context here
        dbContext...
    }
}