Google Donut (Pie) Chart using dynamic data and Web API

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The Google Donut chart is not different from the Pie chart and it is simply a variation of the Pie chart. The Donut however, has a round space in the center of the chart. It uses similar properties of a Pie chart to extract and display data. However, there is one unique option that separates the Donut from the Pie, and that is the “pieHole” option.

Google Donut Chart Example

I have described the Google Pie Chart in my previous article. In that example I have extracted data from an SQL Server database using a Web Service. Here, in this example I’ll create an Asp.Net Web API that will serve the data for the chart. For data extraction, I am using jQuery Ajax.

The SQL Server Table

Let’s first create a table in SQL Server. The table has data with monthly sale figures of books (or any commodity) for an entire year.

CREATE TABLE dbo.Books_Annual_Sales(
    Month varchar(20) NULL,
    SalesFigure int NULL
) ON PRIMARY

Now insert few data in the table. The first column is a varchar that will hold values in the form of month and second column is an int that will hold random figures.

INSERT INTO Books_Annual_Sales (Month, SalesFigure) VALUES ('JAN', 34)
INSERT INTO Books_Annual_Sales (Month, SalesFigure) VALUES ('FEB', 22)
...

Similarly, insert more rows into the table to give the chart more values to display.

Let us now create the API that will serve data to the chart.

The Web API (MVC 4)

Remember: You should have MCV 4 installed on your computer. Therefore, please make sure that you have it.

I am assuming you have some knowledge about creating a Web API in Asp.Net. Don’t worry if you are not well versed with it. I have an article for newbie’s, with an extremely simple and yet useful example.

Related: A Systematic guide to create your First Web API Service in Asp.Net

Model “Books.cs” (C#)
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace BooksApp.Models
{
    public class Books
    {
        public string Month { get; set; }
        public int SalesFigure { get; set; }
    }
}

Also Read: How to Add a Model in Asp.Net Web API project

Model “Books.vb” (Vb.Net)
Imports System.Web

Namespace BooksApp.Models
    Public Class Books
        Public Property Month() As String
            Get
                Return m_Month
            End Get
            Set(value As String)
                m_Month = value
            End Set
        End Property

        Private m_Month As String

        Public Property SalesFigure() As Integer
            Get
                Return m_SalesFigure
            End Get
            Set(value As Integer)
                m_SalesFigure = value
            End Set
        End Property
        Private m_SalesFigure As Integer
    End Class
End Namespace

Next, create the API Controller.

The Controller (C#)
using System;
using System.Collections.Generic;
using System.Net.http;
using System.Web.http;

using BooksApp.Models;
using System.Data.SqlClient;

namespace BooksApp.Controllers
{
    public class BooksController : ApiController
    {

        List<Books> MySales = new List<Books>();

        public IEnumerable<Books> Get()
        {

            string sConnString = "Data Source=DNA;Persist Security Info=False;" +
                "Initial Catalog=DNA_Classified;User Id=sa;Password=;Connect Timeout=30;";

            SqlConnection myConn = new SqlConnection(sConnString);

            SqlCommand objComm = new SqlCommand("SELECT *FROM dbo.Books_Annual_Sales", myConn);
            myConn.Open();

            SqlDataReader reader = objComm.ExecuteReader(); 

            // POPULATE THE LIST WITH DATA.
            while (reader.Read())
            {
                MySales.Add(new Books
                {
                    Month = reader["Month"].ToString(),
                    SalesFigure = (int)reader["SalesFigure"]
                });
            }

            myConn.Close();

            return MySales;
        }
    }
}

Also Read: How to Add a Controller Class in Asp.Net Web API

The Controller (Vb.Net)
Option Explicit On

Imports System.Net.http
Imports System.Web.http

Imports System.Data.SqlClient
Imports BooksApp.BooksApp.Models

Namespace BooksApp
    Public Class BooksController
        Inherits ApiController

        Dim mySales As New List(Of Books)()

        Public Function [Get]() As IEnumerable(Of Books)
            Dim sConnString As String = "Data Source=DNA;Persist Security Info=False;" & _
                "Initial Catalog=DNA_Classified;User Id=sa;Password=;Connect Timeout=30;"

            Dim myConn As New SqlConnection(sConnString)

            Dim objComm As New SqlCommand("SELECT *FROM dbo.Books_Annual_Sales", myConn)

            myConn.Open()

            Dim reader As SqlDataReader = objComm.ExecuteReader()

            ' POPULATE THE LIST WITH DATA.
            While reader.Read()
                mySales.Add(New Books() With { _
                    .Month = reader("Month").ToString(), _
                    .SalesFigure = CInt(reader("SalesFigure")) _
                 })
            End While

            myConn.Close()

            Return mySales          ' FINALLY, RETURN THE LIST.

        End Function
    End Class
End Namespace

Well, we have created our Web API and now we need to create a web page (.htm page) that will show the data extracted from the API to our Donut chart.

The Markup
<!DOCTYPE html>
<html>
<head>
    <title>Google Donut Chart Example with Dynamic Data</title>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
    <script type="text/javascript" src="https://www.google.com/jsapi"></script>
</head>
<body>
    <div id="b_sale" style="width:500px; height:300px;"></div> 
</body>

Inside the <head> tag, I have added the jQuery CDN for Ajax that will get the data from API and the Google API for charts. This API provides the necessary properties and methods to draw the chart.

In the <body> tag, I have a DIV element that serves as the container for the chart.

The Script to Draw the Donut Chart
<script>
    // VISUALIZATION API AND THE PIE CHART PACKAGE.
    google.load("visualization", "1", { packages: ["corechart"] });

    google.setOnLoadCallback(DrawDonut);

    function DrawDonut() {

        var options = {
            title: 'MONTHLY SALE OF BOOKS',
            pieHole: 0.4,                       // SET NUMBER BETWEEN 0 AND 1.
            colors: ['orange', '#56B21F']      // ADD CUSTOM COLORS.
        };

        $.ajax({
            url: '/api/books/',
            dataType: "json",
            type: "GET",
            success: function (data) {

                var arrValues = [['Month', 'Sales Figure']];        // DEFINE AN ARRAY.
                var iCnt = 0;

                $.map(data, function () {
                    arrValues.push([data[iCnt].Month, data[iCnt].SalesFigure]);
                    iCnt += 1;
                });

                // CREATE A DataTable AND ADD THE ARRAY (WITH DATA) IN IT.
                var figures = google.visualization.arrayToDataTable(arrValues)

                // THE TYPE OF CHART. IT’S A PIE CHART, HOWEVER THE “pieHole” OPTION 
                    // (SEE “var options” ABOVE) WILL ADD A SPACE AT THE CENTER FOR DONUT.
                var chart = new google.visualization.PieChart(document.getElementById('b_sale'));

                chart.draw(figures, options);      // DRAW GRAPH WITH THE DATA AND OPTIONS.
            },
            error: function (XMLHttpRequest, textStatus, errorThrown) {
                alert('There was an Error');
            }
        });
    }
</script>
</html>

Related: Create a Google Pie Chart from SQL Server Data using jQuery Ajax and Asp.Net Web Service

Remember, you cannot draw a 3D chart for Donut. If you include the “is3D” option, it will ignore the “pieHole” option. This option is case sensitive. I have added some custom color for my Donut chart, in the options variable. If you ignore the colors option, the API will add random multiple colors to the chart. Its your choice.

That’s it. Thanks for reading.

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