A framework for indexing and querying the ZODB

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ObjectQuery

ObjectQuery is licensed under ZPL 2.1.

Copyright 2007-2009 by gocept gmbh & co. kg.

ObjectQuery enables you to query for persistent objects (e.g. objects in the ZODB). This is done with a XPath-like language named Regular Path Expressions (RPE). ObjectQuery also includes indexstructures for performance reasons.

It uses SimpleParse to parse the RPE-query.

Please report bugs to gocept project portal.

Querying objects with regular path expressions

Initialization

First load the test database. For more information about that, please have a look inside testobjects.py.

>>> from gocept.objectquery.testobjects import *
>>> import ZODB.MappingStorage
>>> import ZODB
>>> from gocept.objectquery.collection import ObjectCollection
>>> storage = ZODB.MappingStorage.MappingStorage()
>>> db = ZODB.DB(storage)
>>> conn = db.open()
>>> dbroot = conn.root()
>>> dbroot['_oq_collection'] = objects = ObjectCollection(conn)
>>> import transaction
>>> import gocept.objectquery.indexsupport
>>> index_synch = gocept.objectquery.indexsupport.IndexSynchronizer()
>>> transaction.manager.registerSynch(index_synch)

>>> p_orwell = Person(name="George Orwell")
>>> p_lotze = Person(name="Thomas Lotze")
>>> p_goethe = Person(name="Johann Wolfgang von Goethe")
>>> p_weitershausen = Person(name="Philipp von Weitershausen")

>>> b_1984 = Book(author=p_orwell,
...               title="1984",
...               written=1990,
...               isbn=3548234100)
>>> b_plone = Book(author=p_lotze,
...                title="Plone-Benutzerhandbuch",
...                written=2008,
...                isbn=3939471038)
>>> b_faust = Book(author=p_goethe,
...                title="Faust",
...                written=1811,
...                isbn=3406552501)
>>> b_farm = Book(author=p_orwell,
...               title="Farm der Tiere",
...               written=2002,
...               isbn=3257201184)
>>> b_zope = Book(author=p_weitershausen,
...               title="Web Component Development with Zope 3",
...               written=2007,
...               isbn=3540338071)

>>> l_halle = Library(location="Halle",
...                   books=[b_1984, b_plone, b_farm, b_zope])
>>> l_berlin = Library(location="Berlin",
...                    books=[b_1984, b_plone, b_faust, b_farm, b_zope])
>>> l_chester = Library(location="Chester",
...                     books=[b_1984, b_faust, b_farm])

>>> dbroot['librarydb'] = persistent.list.PersistentList()
>>> dbroot['librarydb'].extend([l_halle, l_berlin, l_chester])

>>> librarydb = dbroot['librarydb']
>>> transaction.commit()

>>> from pprint import pprint

Create QueryProcessor and initialize the ObjectCollection

You create a QueryProcessor like this:

>>> from gocept.objectquery.pathexpressions import RPEQueryParser
>>> from gocept.objectquery.processor import QueryProcessor
>>> parser = RPEQueryParser()
>>> query = QueryProcessor(parser, objects)
>>> query
<gocept.objectquery.processor.QueryProcessor object at 0x...>

Some example usecases

Root joins:

>>> r = query('/PersistentList/Library')
>>> sorted(elem.location for elem in r)
['Berlin', 'Chester', 'Halle']

Search for the authors of all Books named “Faust”:

>>> r = query('/PersistentList/Library/Book[@title="Faust"]/Person')
>>> sorted(elem.name for elem in r)
['Johann Wolfgang von Goethe']

Search for all books written after year 2000:

>>> r = query('/PersistentList/Library/Book[@written>=2000]')
>>> len(r)
3
>>> pprint(sorted(elem.title for elem in r))
['Farm der Tiere',
 'Plone-Benutzerhandbuch',
 'Web Component Development with Zope 3']

Search for all authors of books written after year 2000:

>>> r = query('/PersistentList/Library/Book[@written>=2000]/Person')
>>> len(r)
3
>>> pprint(sorted(elem.name for elem in r))
['George Orwell', 'Philipp von Weitershausen', 'Thomas Lotze']

Search for all Books, that have are located in Halle and have been written in 2007:

>>> r = query('/PersistentList/Library[@location="Halle"]/Book[@written==2007]')
>>> sorted((elem.title, elem.isbn) for elem in r)
[('Web Component Development with Zope 3', 3540338071L)]

Handle Wildcards correctly:

>>> r = query('/PersistentList/Library/_/Person')
>>> pprint(sorted(elem.name for elem in r))
['George Orwell',
 'Johann Wolfgang von Goethe',
 'Philipp von Weitershausen',
 'Thomas Lotze']

What about precedence:

>>> r = query('/PersistentList/Library[@location="Halle"]/Book/Person')
>>> pprint(sorted(elem.name for elem in r))
['George Orwell', 'Philipp von Weitershausen', 'Thomas Lotze']

>>> r = query('(/PersistentList/Library[@location="Halle"]/Book)/Person')
>>> pprint(sorted(elem.name for elem in r))
['George Orwell', 'Philipp von Weitershausen', 'Thomas Lotze']

>>> r = query('/PersistentList/Library[@location="Halle"]/(Book/Person)')
>>> len(r)
0
>>> r = query('(/PersistentList/Library/Book[@title="Faust"])/(Book/Person)')
>>> sorted(elem.name for elem in r)
['Johann Wolfgang von Goethe']

But pay attention. If you change the query from ..”]/(Book.. to ..”](/Book.. you get an Library-Result with location in “Halle”. This is, because the subquery (in brakets) returns no results:

>>> r = query('/PersistentList/Library[@location="Halle"](/Book/Person)')
>>> len(r)
1
>>> r[0].location
'Halle'

Unions:

>>> r = query('(/PersistentList/Library[@location="Halle"])|(Book/Person)')
>>> len(r)
5
>>> pprint(sorted(elem for elem in r))
[<gocept.objectquery.testobjects.Library object at 0x...>,
 <gocept.objectquery.testobjects.Person object at 0x...>,
 <gocept.objectquery.testobjects.Person object at 0x...>,
 <gocept.objectquery.testobjects.Person object at 0x...>,
 <gocept.objectquery.testobjects.Person object at 0x...>]

>>> r = query('(/PersistentList/Library)|(Book[@written=1990])')
>>> len(r)
4
>>> pprint(sorted(elem for elem in r))
[<gocept.objectquery.testobjects.Book object at 0x...>,
 <gocept.objectquery.testobjects.Library object at 0x...>,
 <gocept.objectquery.testobjects.Library object at 0x...>,
 <gocept.objectquery.testobjects.Library object at 0x...>]

>>> transaction.commit()

Kleene Closure

First we need a new database:

>>> doc1 = Document()
>>> doc2 = Document()
>>> doc3 = Document()
>>> fol4 = Folder([doc2])
>>> fol3 = Folder([doc1])
>>> fol2 = Folder([fol3])
>>> fol1 = Folder([fol2])
>>> plo1 = Plone([fol1, fol4, doc3])
>>> root = Root([plo1])

>>> dbroot['test'] = root
>>> transaction.commit()

Now there should be one Plone object under root:

>>> r = query('/Root/Plone')
>>> len(r) == 1 and r[0] == plo1
True

>>> r = query('/Root/Plone/Folder/Document')
>>> len(r)
1
>>> r[0] == doc2
True

Get all Documents which are under any number of Folders:

>>> r = query('/Root/Plone/Folder*/Document')
>>> r[0] != r[1] != r[2] and isinstance(r[0], Document)
True

>>> r = query('Plone/Folder*/Document')
>>> r[0] != r[1] != r[2] and isinstance(r[0], Document)
True

>>> r = query('Folder*/Document')
>>> r[0] != r[1] != r[2] and isinstance(r[0], Document)
True

Get all Documents which are under one or zero number of Folders:

>>> r = query('/Root/Plone/Folder?/Document')
>>> len(r) == 2 and (r[0] == doc2 or r[1] == doc2) and (r[0] == doc3 or r[1] == doc3) and r[0] != r[1]
True

>>> r = query('Folder?/Document')
>>> len(r) == 3 and r[0] != r[1] != r[2]
True

Get all Documents which are under one or more number of Folders:

>>> r = query('/Root/Plone/Folder+/Document')
>>> len(r) == 2 and (r[0] == doc1 or r[1] == doc1) and (r[0] == doc2 or r[1] == doc2) and r[0] != r[1]
True

>>> r = query('Folder+/Document')
>>> len(r) == 2 and (r[0] == doc1 or r[1] == doc1) and (r[0] == doc2 or r[1] == doc2) and r[0] != r[1]
True

You may also query absolute path lengths:

>>> len(query('Plone/Document'))
1
>>> len(query('Plone/Folder/Document'))
1
>>> len(query('Plone/Folder/Folder/Document'))
0
>>> len(query('Plone/Folder/Folder/Folder/Document'))
1

Furthermore, it is possible to query all Documents, which are located under 2 or more Folders:

>>> r = query('Plone/Folder+/Folder/Document')
>>> len(r) == 1 and r[0] == doc1
True

>>> r = query('Plone/Folder/Folder+/Document')
>>> len(r) == 1 and r[0] == doc1
True

A special case is the combination of wildcard and ‘*’ closure:

>>> r = query('Plone/_*/Document')
>>> len(r) == 3
True

CHANGES

0.1 (unreleased)

0.1a (2009-02-04)

  • first alpha release

0.1pre (2008-08-19)

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