#16187: Refactor lookup system
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Reporter: UloPe | Owner: akaariai
Type: | Status: assigned
Cleanup/optimization | Version: master
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Accepted
Severity: Normal | Needs documentation: 0
Keywords: | Patch needs improvement: 1
Has patch: 1 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Comment (by akaariai):
I did a little more work on the API. I am confident it is general enough
yet simple enough now.
I created a quick-and-dirty HStoreField implementation, I'll attach a
ready to run project. Quick instructions: edit database settings to point
to a db with hstore extension installed, syncdb and run python tester.py.
The interesting bits are in testproject/hstore.py. I'll paste that portion
in here:
{{{
from django.db.models import TextField, Lookup, Extract
# This one implements "get value of key X from the hstore". The
# value is extracted from the hstore, and so further lookups on
# the value are possible. The extracted values are of type text
# in the DB, so output_type = TextField().
class HStoreExtract(Extract):
output_type = TextField()
def as_sql(self, qn, connection):
lhs, params = qn.compile(self.lhs)
# extracts know the lookups used for creating them,
# so init_lookups[0] gives us the 'somekey' in
# hstorefield__somekey='foo'
params.append(self.init_lookups[0])
return '%s -> %%s' % (lhs), params
# This one implements "does hstore contain key X". This is a
# a lookup on the hstore field itself.
class HStoreContains(Lookup):
lookup_name = 'hcontains'
def as_sql(self, qn, connection):
lhs, params = self.process_lhs(qn, connection)
rhs, rhs_params = self.process_rhs(qn, connection)
params.extend(rhs_params)
return '%s ? %s' % (lhs, rhs), params
# Main HStoreField
class HStoreField(TextField):
# Following two methods needed for createdb & save support.
def db_type(self, connection):
return 'hstore'
def get_db_prep_save(self, value, connection):
data = []
for k, v in value.items():
data.append('%s=>%s' % (k, v))
return ','.join(data)
def get_lookup(self, lookup):
found_lookup = None
# It is possible to rename Django's own lookups so that conflicts
# between common names (contains, exact for example) can be
avoided.
if lookup.startswith('dj_'):
# If it started with 'dj_' use Django's own lookups
found_lookup = super(HStoreField, self).get_lookup(lookup[3:])
# If it wasn't something existing, then interpret as extract key
from
# hstore
if found_lookup is None:
return HStoreExtract
else:
return found_lookup
HStoreField.register_lookup(HStoreContains)
}}}
Using HStoreField it is possible to do queries like
`qs.filter(hstoredata__somekey__icontains='foobar')`.
The test project contains some examples which go a bit further.
Now, docs need rewriting and this one is RFC.
--
Ticket URL: <https://code.djangoproject.com/ticket/16187#comment:35>
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