Enabling Programmable Self with HealthVault

Creating Custom Types

Extending a HealthVault data type might not always solve your data needs. Many times there are legitimate use cases for which the application needs a unique data repository. For example, in our Quantified Self application, we need a repository to store all of the user’s self-experiments.

HealthVault provides a mechanism called an application-specific type for this purpose. This type is not shareable with other applications. Once application developers find a broader use for their data, they can work with Microsoft to create a first-class data type for their needs.

Example 4-11 shows how one can use an application-specific type to store self-experiment hypotheses for the Quantified Self application. In our application we are asking a user to create a hypothesis using a simple text box. The value of this text box is read as the hypothesis string in Line . In Lines –, we create an XML document with the data for this specific type and then add it to the document using ApplicationSpecificXml in Line . Each application-specific type requires a SubtypeTag and Description (Lines –). We also specify the application creating this type in Line . Additionally, we use the common note element to capture the status of the type in Line , and the When element captures the date.

Example 4-11. Writing an application-specific custom type

    protected void Btn_Submit_Hypothesis_Click(object sender, System.EventArgs e)
    {
        ApplicationSpecific appSpecific = new ApplicationSpecific();
        string hypothesis = Txt_Hypothesis.Text; 
        appSpecific.ApplicationId = this.ApplicationConnection.ApplicationId.ToString(); 
        XmlDocument xml = new XmlDocument(); 
        xml.LoadXml(
            string.Format("<self-experiment><hypothesis>{0}</hypothesis>
                </self-experiment>", 
            hypothesis)); 
        appSpecific.ApplicationSpecificXml.Add(xml); 
        appSpecific.SubtypeTag = "self-experiment"; 
        appSpecific.Description = hypothesis; 
        // Default the status note to active when the hypothesis is created
        appSpecific.CommonData.Note = "Active"; 
        appSpecific.When = new HealthServiceDateTime(DateTime.Now);
        PersonInfo.SelectedRecord.NewItem(appSpecific); 
    }

On the other hand, we can show the list of self-experiments by reading the ApplicationSpecificXml using an XPath navigator. In Example 4-12, note that in Lines –, we assume that the document for this type contains only one element and that the first node is the hypothesis.

Example 4-12. Reading an application-specific type

    private void DisplaySelfExperiments(List<ApplicationSpecific> selfExperiments)
    {
        DataTable selfExperiment = new DataTable("SelfExperiments");
        selfExperiment.Columns.Add(new DataColumn("Date"));
        selfExperiment.Columns.Add(new DataColumn("Hypothesis"));
        selfExperiment.Columns.Add(new DataColumn("Status"));
        foreach (ApplicationSpecific s in selfExperiments)
        {
            
            DataRow row = selfExperiment.NewRow();
            row["Date"] = s.EffectiveDate.ToShortDateString().ToString();
            row["Hypothesis"] = s.ApplicationSpecificXml[0].CreateNavigator(). 
                                SelectSingleNode("hypothesis").Value; 
            row["Status"] = s.CommonData.Note;
            selfExperiment.Rows.Add(row);
        }
        SelfExperimentsView.DataSource = selfExperiment;
        SelfExperimentsView.DataBind();
    }