Defining and Using Classes
Defining and Using XData Blocks
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An
XData block is a class member that consists of a name and a unit of data that you include in a class definition for use by the class after compilation. This chapter discusses XData blocks and covers the following topics:
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An
XData block is a named unit of data that you include in a class definition, typically for use by a method in the class. Most frequently, it is a well-formed XML document, but it could consist of other forms of data, such as JSON.
You can create an XData block by typing it directly in Atelier.
An XData block is a named class member (like properties, methods, and so on). The available XData block keywords include:
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SchemaSpec — Optionally specifies an XML schema against which the XData can be validated.
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XMLNamespace — Optionally specifies the XML namespace to which the XData block belongs. You can also, of course, include namespace declarations within the XData block itself.
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If used to store XML, the XData block must consist of one root XML element, with any valid contents.
An XData block is useful if you want to define a small amount of system data. For example, suppose that the
EPI.AllergySeverity class includes the properties
Code (for internal use) and
Description (for display to the users). This class could include an XData block like the following:
XData LoadData
{
<table>
<row>1^Minor</row>
<row>2^Moderate</row>
<row>3^Life-threatening</row>
<row>9^Inactive</row>
<row>99^Unable to determine</row>
</table>
}
The same class could also include a class method that reads this XData block and populates the table, as follows:
/// called by EPI.Utils.GenerateData
ClassMethod Setup() As %Status
{
//first kill extent
do ..%KillExtent()
// Get a stream of XML from the XData block contained in this class
Set xdataID="EPI.AllergySeverity||LoadData"
Set compiledXdata=##class(%Dictionary.CompiledXData).%OpenId(xdataID)
Set tStream=compiledXdata.Data
If '$IsObject(tStream) Set tSC=%objlasterror Quit
set status=##class(%XML.TextReader).ParseStream(tStream,.textreader)
//check status
if $$$ISERR(status) do $System.Status.DisplayError(status) quit
//iterate through document, node by node
while textreader.Read()
{
if (textreader.NodeType="chars")
{
set value=textreader.Value
set obj=..%New()
set obj.Code=$Piece(value,"^",1)
set obj.Description=$Piece(value,"^",2)
do obj.%Save()
}
}
}
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The XML within the XData is minimal. That it, instead of presenting the allergy severities as XML element with their own elements or attributes, the XData block simply presents rows of data as delimited strings. This approach allows you to write the setup data in a visually compact form.
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A class could also include an XData block containing JSON content, like the following:
XData LoadJSONData [MimeType = "application/json"]
{
{
"person":"John",
"age":30,
"car":"Ford"
}
}
The same class could also include a class method that reads this XData block and populates a dynamic object, as follows:
/// Reads a JSON XData block
ClassMethod SetupJSON() As %Status
{
// Get a stream of JSON from the XData block contained in this class
Set xdataID="Demo.XData||LoadJSONData"
Set compiledXdata=##class(%Dictionary.CompiledXData).%OpenId(xdataID)
Set tStream=compiledXdata.Data
If '$IsObject(tStream) Set tSC=%objlasterror Quit
// Create a dynamic object from the JSON content and write it as a string
Set dynObject = {}.%FromJSON(tStream)
Write dynObject.%ToJSON()
}
Content Date/Time: 2019-02-20 22:42:10
