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"""
An XML Foreign Data Wrapper.
"""
from . import ForeignDataWrapper
from xml.sax import ContentHandler, make_parser
class MulticornXMLHandler(ContentHandler):
def __init__(self, elem_tag, columns):
self.elem_tag = elem_tag
self.columns = columns
self.reset()
def reset(self):
self.parsed_rows = []
self.current_row = {}
self.tag = None
self.root_seen = 0
self.nested = False
def startElement(self, name, attrs):
if name == self.elem_tag:
# Keep track of nested "elem_tag"
self.root_seen += 1
elif self.root_seen == 1:
# Ignore nested tag.
if name in self.columns:
self.tag = name
self.current_row[name] = ''
def characters(self, content):
if self.tag is not None:
self.current_row[self.tag] += content
def get_rows(self):
"""Return the parsed_rows, and forget about it."""
result, self.parsed_rows = self.parsed_rows, []
return result
def endElement(self, name):
if name == self.elem_tag:
self.root_seen -= 1
self.parsed_rows.append(self.current_row)
self.current_row = {}
elif name in self.columns:
self.tag = None
class XMLFdw(ForeignDataWrapper):
"""A foreign data wrapper for accessing xml files.
Valid options:
- filename: full path to the xml file.
- elem_tag: a tagname acting as a root for a tag.
Child tag will be mapped to corresponding columns.
"""
def __init__(self, fdw_options, fdw_columns):
super(XMLFdw, self).__init__(fdw_options, fdw_columns)
self.filename = fdw_options['filename']
self.elem_tag = fdw_options['elem_tag']
self.buffer_size = fdw_options.get('buffer_size', 4096)
self.columns = fdw_columns
def execute(self, quals, columns):
parser = make_parser()
handler = MulticornXMLHandler(self.elem_tag, self.columns)
parser.setContentHandler(handler)
with open(self.filename) as stream:
while(True):
a = stream.read(self.buffer_size)
if not a:
break
parser.feed(a)
for row in handler.get_rows():
yield row
parser.close()
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