In part two of this tutorial series we will focus on developing a simple mobile back-end service.

We are going to build a simple mobile sales application, this application will have only two basic entities

1.  Products (stored in a server database)
2. Sales (created on mobile but synced to the online database periodically)

Building a Mobile Sales solution Back-end

We are going to use NancyFx framework to build the mobile back-end service to serve as an API for our mobile application. If you are not a .Net developer don’t worry i promise to write another post using a language of choice.

IDE: Visual Studio 2013/2012/2010

Step 1. Starting a new NancyFx project

There are many ways of starting a Nancyfx project but the simplest way of starting one is downloading the nancyfx visual studio template which will help you choose the appropriate project template.  NB: NancyFx is very well documented and has an amazing tutorial on how to start a new project. If you are a total newbie.

You can host a Nancyfx project in many different ways (IIS (Azure, Asp.net), Self Hosted, Ngnix, FastCgi ) in this tutorial we will host our solution on Azure.

If you have downloaded and installed the Nancy project template,  Start a new project, select Web > Nancy Application with ASP.NET Hosting. Give the Project a name : MobileSales

The project directory will look like this:

Module Concept:  Nancy was designed to handle all application behavior inside a Module, inside a module you can define the application request routing and behavior.

Open the IndexModule.cs replace the entire

Get["/"] = parameters =>{
......
}

with this simple line of code.

   
  Get["/"] = parameters => Response.AsText("you are here");

Run the application.
The result will be as follows.

Deep Dive

We are going straight to developing our application if you need to learn how NancyFx works kindly take a detour on onto it’s  official wiki,   You can also search  entire web for many other tutorials on how NancyFx works.

Step 2. Create data models for our solution

In this solution we will use Entity Framework as our ORM framework for this solution.  Using Nuget Package Manager Console, execute command below to add Entity Framework library into your project.

PM> Install-Package EntityFramework 

We are going to use these two entities in our solution.
1. Product
2. Sale

Create new class Sales.cs

namespace MobileSales.Models
{
   public class Sale {
     public int Id { get; set; }
     public int Items { get; set; }
     public double Amount { get; set; }
     public Product SaleItem { get; set; }
   }
}

Create new class Product.cs

namespace MobileSales.Models
{
   public class Product {
     public int Id { get; set; }
     public string Name { get; set; }
     public double Price { get; set; }
     public virtual List<Sale> Sales { get; set; }
  }
}

Step 3 Creating a DbContext
A DBContext is the primary class that is responsible for interacting with your SQL Database.  Here we register all the entities that we are going to work with.

Create a class SalesContext

using System.Data.Entity;
using MobileSales.Models;

namespace MobileSales
{
    public class SalesContext : DbContext
    {
        public SalesContext():base("DefaultConnection"){}
        public DbSet Products { get; set; }
        public DbSet Sales { get; set; }
    }
}

Step 4: Create a Database initializer.
A database initializer is a class that takes care of database creation and initialization in a Code First application. It is the job of database initializer to create the database and required tables based on the data model classes you create. This initializer will help us create the database and also seed it with some sample data for use.

Create a class DbInitializer

using System.Collections.Generic;
using System.Data.Entity;

namespace MobileSales
{
    public class DbInitializer:CreateDatabaseIfNotExists
    {
        protected override void Seed(SalesContext context)
        {
            base.Seed(context);
            //Create some sample products.
            List products = new List()
            {
                new Product(){Name = "Apples",Price = 20},
                new Product(){Name = "Mango",Price = 20},
                new Product(){Name = "Pear",Price = 5},
                new Product(){Name = "Banana",Price = 5},
                new Product(){Name = "Pineapple",Price = 150},
            };
            context.Products.AddRange(products);
            context.SaveChanges();
        }
    }
}

To ensure that the initializer is executed at the start of the application: Open Bootstrapper.cs
and override ApplicationStartup method.
Add the following lines of code

Database.SetInitializer(new DbInitializer());

Your Bootstrapper should look like this.

using System.Data.Entity;
using Nancy.Bootstrapper;
using Nancy.TinyIoc;
using Nancy;

namespace MobileSales
{
    public class Bootstrapper : DefaultNancyBootstrapper
    {
        // The bootstrapper enables you to reconfigure the composition of the framework,
        // by overriding the various methods and properties.
        // For more information https://github.com/NancyFx/Nancy/wiki/Bootstrapper
        protected override void ApplicationStartup(TinyIoCContainer container, IPipelines pipelines)
        {
            base.ApplicationStartup(container, pipelines);
            //Specify the database initializer. 
            Database.SetInitializer(new DbInitializer());
        }
    }
}

Step 5: Implement API endpoints.
We are going to implement 2 API methods that our mobile application will access.
1. To fetch products
2. Post sales

Inside IndexModule.cs
Implement the following methods below

Get["/"] = parameters => Response.AsText("you are here");

            Get["/products"] = parameters =>
            {
                //fetch products from db. 
                var products = new SalesContext().Products.ToList();
                return Response.AsJson(products);
            };

            Post["/sale"] = parameters =>
            {
                //Mapping our POST JSON request to a Sale Object.  
                var sale = this.Bind();
                var ctx = new SalesContext();
                ctx.Sales.Add(sale);
                ctx.SaveChanges();
                return Response.AsJson(sale);
            };

Step 6: Creating local database.
This step requires an installation of SQL Server Express or SQL Server.

In your project create a folder App_Data, this is where the database file will live. Right click the App_Data folder then navigate to Add -> SQL Server Database. You will be prompted to pick a name, enter SalesDb remember this name.

Once we have the database created we will need to connect our application to this database, this we specify using a connection string inside the Web.config file.

Open Web.config file and insert the following code:

 <?xml version="1.0" encoding="utf-8"?>
<configuration>
 ..............
   <connectionStrings>
    <add name="DefaultConnection" connectionString="Data Source=(LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\SalesDb.mdf;Initial Catalog=SalesDb;Integrated Security=True"
      providerName="System.Data.SqlClient" />
  </connectionStrings>
  .................
</configuration>

Step 7: Testing.
Run the application and type

http://localhost:12008/products

The browser should output a list of products in JSON.

Step 7: Publishing to Azure.. .
For the sake of brevity, i will forward you to this tutorial on how to publish to windows azure. I have published mine and it’s living here.

Conclusion:
In this series we have tried to build a simple Mobile service back-end using NancyFX framework. In the 3rd part of this series we are going to build an android application that connects to this mobile back-end service.

See you on the next post, comments are welcomed.

Download the Source Code here…