Using XUpdate

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4Suite contains an implementation of XUpdate, the XML Update Language. XUpdate is essentially an XPath-based XML transformation language, like XSLT. An XUpdate document is an XML document that specifies what changes should be made to another XML document.

XUpdate is neither a W3C Recommendation nor an ISO or IETF standard. It is just a project of the XML:DB Initiative's XUpdate Working Group, and it never advanced beyond a Working Draft published in September, 2000. It is not very well specified, but it is fairly convenient and enables a basic level of functionality, so it has enjoyed popularity in a number of implementations.

4Suite's XUpdate implementation, 4XUpdate, consists of a Python API (via the Ft.Xml.XUpdate module) and a command-line script (4xupdate). The APIs involve taking a source document (the XML to be updated) and an XUpdate document (the changes to apply), and either producing a new document or updating the source document in-place.

The Python API can be invoked directly on Domlette objects or on InputSources. Here is an example of using the ApplyXUpdate convenience function, which takes InputSources: 

from Ft.Xml.Domlette import PrettyPrint
from Ft.Xml.InputSource import DefaultFactory
try:
    from Ft.Xml.XUpdate import ApplyXUpdate
except ImportError:
    # the function name changed between 1.0a3 and 1.0b1
    from Ft.Xml.XUpdate import ApplyXupdate as ApplyXUpdate

SOURCE='''<?xml version = "1.0"?>
<ADDRBOOK xmlns="http://bogus/">
  <ENTRY ID="fr">
    <NAME>fred</NAME>
  </ENTRY>
</ADDRBOOK>'''

XU='''<?xml version="1.0"?>
<xu:modifications version="1.0" xmlns:xu="http://www.xmldb.org/xupdate"
  xmlns:myns="http://bogus/">
  <xu:append select="/myns:ADDRBOOK" child="last()">
    <ENTRY ID="vz">
      <NAME>Vasia Zhugenev</NAME>
    </ENTRY>
  </xu:append>
</xu:modifications>'''

src_isrc = DefaultFactory.fromString(SOURCE, "http://test1/")
xup_isrc = DefaultFactory.fromString(XU, "http://test2/")

result_dom = ApplyXUpdate(src_isrc, xup_isrc)
PrettyPrint(result_dom)

#expected:
#<?xml version="1.0" encoding="UTF-8"?>
#<ADDRBOOK xmlns="http://bogus/">
#  <ENTRY ID="fr">
#    <NAME>fred</NAME>
#  </ENTRY>
#<ENTRY ID="vz">
#    <NAME>Vasia Zhugenev</NAME>
#  </ENTRY>
#</ADDRBOOK>

If you have both the source document and XUpdate document as Domlette nodes already, you can use the XUpdate processor directly: 

# add to the above script...
from Ft.Xml.Domlette import NonvalidatingReader
from Ft.Xml.XUpdate import Processor
src_isrc = DefaultFactory.fromString(SOURCE, "http://test1/")
xup_isrc = DefaultFactory.fromString(XU, "http://test2/")
src_dom = NonvalidatingReader.parse(src_isrc)
xup_dom = NonvalidatingReader.parse(xup_isrc)
proc = Processor()
proc.execute(src_dom, xup_dom)
# src_dom has been modified in-place
PrettyPrint(src_dom)

Using the processor directly allows you to set XPath variables, if needed: 

from Ft.Xml import EMPTY_NAMESPACE
# execute with $x='foo'
proc.execute(src_dom, xup_dom, {(EMPTY_NAMESPACE, u'x'): u'foo'})

The command-line script works on local files or even URIs, if resolvable, and normally sends the result XML to standard output, although it can also be made to write to a file. See "4xupdate -h" for usage instructions.

All of XUpdate (such as it's spec'ed) is currently implemented.

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