public class IndexModel : PageModel
{
    public ChartJs BarChart { get; set; }
    public string ChartJson { get; set; }

    public IndexModel(DB db)
    {
        BarChart = new ChartJs();   // must initialise the ChartJs object in the constructor
        this.db = db;
    }

    public void OnGet(){} 
}   //end of class

    public void OnGet()
    {
        Dictionary<string, double> favCodeEditors = db.getFavouriteCodeEditors();

        setUpBarChart(favCodeEditors);
    } 

    private void setUpBarChart(Dictionary<string,int> dataToDisplay)
        {
            try
            {
                // 1. set up chart options
                BarChart.type = "bar";
                BarChart.options.responsive = true;

                // 2. separate the received Dictionary data into labels and data arrays
                var labelsArray = new List<string>();
                var dataArray = new List<double>();

                foreach (var data in dataToDisplay)
                {
                    labelsArray.Add(data.Key);
                    dataArray.Add(data.Value);
                }

                BarChart.data.labels = labelsArray;

                // 3. set up a dataset
                var firsDataset = new Dataset();
                firsDataset.label = "Number of votes";
                firsDataset.data = dataArray.ToArray();

                BarChart.data.datasets.Add(firsDataset);

                // 4. finally, convert the object to json to be able to inject in HTML code
                ChartJson = JsonConvert.SerializeObject(BarChart, new JsonSerializerSettings
                {
                    NullValueHandling = NullValueHandling.Ignore,
                });
            }
            catch (Exception e)
            {
                Console.WriteLine("Error initialising the bar chart inside Index.cshtml.cs");
                throw e;
            }
        }

    public Dictionary<string, int> getFavouriteCodeEditors()
        {
            Dictionary<string, int> labelsAndCounts = new Dictionary<string, int>();

            try
            {
                con.Open();

                string query = "select code_editor, count(code_editor) as count from student_info group by code_editor";

                SqlCommand cmd = new SqlCommand(query, con);

                SqlDataReader sdr = cmd.ExecuteReader();

                // store labels and counts inside the dictionary
                while (sdr.Read())
                {
                    labelsAndCounts.Add(sdr["code_editor"].ToString(), (int)sdr["count"]);
                }
            }
            catch (Exception e)
            {
                throw e;
            }
            finally { con.Close(); }

            return labelsAndCounts;
        }