"""illustrates an explicit way to persist an XML document expressed using ElementTree. This example explicitly marshals/unmarshals the ElementTree document into mapped entities which have their own tables. Compare to pickle.py which uses pickle to accomplish the same task. Note that the usage of both styles of persistence are identical, as is the structure of the main Document class. """ ################################# PART I - Imports/Coniguration #################################### from sqlalchemy import (MetaData, Table, Column, Integer, String, ForeignKey, Unicode, and_, create_engine) from sqlalchemy.orm import mapper, relationship, Session, lazyload import sys, os, StringIO, re from xml.etree import ElementTree e = create_engine('sqlite://') meta = MetaData() ################################# PART II - Table Metadata ######################################### # stores a top level record of an XML document. documents = Table('documents', meta, Column('document_id', Integer, primary_key=True), Column('filename', String(30), unique=True), Column('element_id', Integer, ForeignKey('elements.element_id')) ) # stores XML nodes in an adjacency list model. This corresponds to # Element and SubElement objects. elements = Table('elements', meta, Column('element_id', Integer, primary_key=True), Column('parent_id', Integer, ForeignKey('elements.element_id')), Column('tag', Unicode(30), nullable=False), Column('text', Unicode), Column('tail', Unicode) ) # stores attributes. This corresponds to the dictionary of attributes # stored by an Element or SubElement. attributes = Table('attributes', meta, Column('element_id', Integer, ForeignKey('elements.element_id'), primary_key=True), Column('name', Unicode(100), nullable=False, primary_key=True), Column('value', Unicode(255))) meta.create_all(e) #################################### PART III - Model ############################################# # our document class. contains a string name, # and the ElementTree root element. class Document(object): def __init__(self, name, element): self.filename = name self.element = element def __str__(self): buf = StringIO.StringIO() self.element.write(buf) return buf.getvalue() #################################### PART IV - Persistence Mapping ################################# # Node class. a non-public class which will represent # the DB-persisted Element/SubElement object. We cannot create mappers for # ElementTree elements directly because they are at the very least not new-style # classes, and also may be backed by native implementations. # so here we construct an adapter. class _Node(object): pass # Attribute class. also internal, this will represent the key/value attributes stored for # a particular Node. class _Attribute(object): def __init__(self, name, value): self.name = name self.value = value # setup mappers. Document will eagerly load a list of _Node objects. mapper(Document, documents, properties={ '_root':relationship(_Node, lazy='joined', cascade="all") }) mapper(_Node, elements, properties={ 'children':relationship(_Node, cascade="all"), # eagerly load attributes 'attributes':relationship(_Attribute, lazy='joined', cascade="all, delete-orphan"), }) mapper(_Attribute, attributes) # define marshalling functions that convert from _Node/_Attribute to/from ElementTree objects. # this will set the ElementTree element as "document._element", and append the root _Node # object to the "_root" mapped collection. class ElementTreeMarshal(object): def __get__(self, document, owner): if document is None: return self if hasattr(document, '_element'): return document._element def traverse(node, parent=None): if parent is not None: elem = ElementTree.SubElement(parent, node.tag) else: elem = ElementTree.Element(node.tag) elem.text = node.text elem.tail = node.tail for attr in node.attributes: elem.attrib[attr.name] = attr.value for child in node.children: traverse(child, parent=elem) return elem document._element = ElementTree.ElementTree(traverse(document._root)) return document._element def __set__(self, document, element): def traverse(node): n = _Node() n.tag = unicode(node.tag) n.text = unicode(node.text) n.tail = unicode(node.tail) n.children = [traverse(n2) for n2 in node] n.attributes = [_Attribute(unicode(k), unicode(v)) for k, v in node.attrib.iteritems()] return n document._root = traverse(element.getroot()) document._element = element def __delete__(self, document): del document._element document._root = [] # override Document's "element" attribute with the marshaller. Document.element = ElementTreeMarshal() ########################################### PART V - Basic Persistence Example ##################### line = "\n--------------------------------------------------------" # save to DB session = Session(e) # get ElementTree documents for file in ('test.xml', 'test2.xml', 'test3.xml'): filename = os.path.join(os.path.dirname(__file__), file) doc = ElementTree.parse(filename) session.add(Document(file, doc)) print "\nSaving three documents...", line session.commit() print "Done." print "\nFull text of document 'text.xml':", line document = session.query(Document).filter_by(filename="test.xml").first() print document ############################################ PART VI - Searching for Paths ######################### # manually search for a document which contains "/somefile/header/field1:hi" d = session.query(Document).join('_root', aliased=True).filter(_Node.tag==u'somefile').\ join('children', aliased=True, from_joinpoint=True).filter(_Node.tag==u'header').\ join('children', aliased=True, from_joinpoint=True).filter( and_(_Node.tag==u'field1', _Node.text==u'hi')).one() print d # generalize the above approach into an extremely impoverished xpath function: def find_document(path, compareto): j = documents prev_elements = None query = session.query(Document) attribute = '_root' for i, match in enumerate(re.finditer(r'/([\w_]+)(?:\[@([\w_]+)(?:=(.*))?\])?', path)): (token, attrname, attrvalue) = match.group(1, 2, 3) query = query.join(attribute, aliased=True, from_joinpoint=True).filter(_Node.tag==token) attribute = 'children' if attrname: if attrvalue: query = query.join('attributes', aliased=True, from_joinpoint=True).filter( and_(_Attribute.name==attrname, _Attribute.value==attrvalue)) else: query = query.join('attributes', aliased=True, from_joinpoint=True).filter( _Attribute.name==attrname) return query.options(lazyload('_root')).filter(_Node.text==compareto).all() for path, compareto in ( (u'/somefile/header/field1', u'hi'), (u'/somefile/field1', u'hi'), (u'/somefile/header/field2', u'there'), (u'/somefile/header/field2[@attr=foo]', u'there') ): print "\nDocuments containing '%s=%s':" % (path, compareto), line print [d.filename for d in find_document(path, compareto)]