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4. Using the HealthVault Data Ecosystem ... > 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();
}