def test_uses_backend_specific_quoting(self):
"""Backend-specific quotes should be used
Table and field names should be quoted with the quote_name
function provided by the database backend. The test here
is a bit trivial since a real-life test case with
PostgreSQL schema tricks or other table/field name munging
would be difficult.
"""
qn = db.connection.ops.quote_name
qs = _select_related_instances(Entry, 'id', [1],
'batch_select_entry', 'section_id')
sql = qs.query.as_sql()[0]
self.failUnless(sql.startswith('SELECT (%s.%s) AS ' %(
qn('batch_select_entry'), qn('section_id'))))
def test_uses_backend_specific_quoting(self):
"""Backend-specific quotes should be used
Table and field names should be quoted with the quote_name
function provided by the database backend. The test here
is a bit trivial since a real-life test case with
PostgreSQL schema tricks or other table/field name munging
would be difficult.
"""
qn = db.connection.ops.quote_name
qs = _select_related_instances(Entry, 'section', [1],
'batch_select_entry', 'section_id')
db.reset_queries()
list(qs)
sql = db.connection.queries[-1]['sql']
self.failUnless(
sql.startswith('SELECT (%s.%s) AS ' %
(qn('batch_select_entry'), qn('section_id'))))
def batch_select(model, instances, target_field_name, fieldname, filter=None):
'''
basically do an extra-query to select the many-to-many
field values into the instances given. e.g. so we can get all
Entries and their Tags in two queries rather than n+1
returns a list of the instances with the newly attached fields
batch_select(Entry, Entry.objects.all(), 'tags_all', 'tags')
would return a list of Entry objects with 'tags_all' fields
containing the tags for that Entry
filter is a function that can be used alter the extra-query - it
takes a queryset and returns a filtered version of the queryset
NB: this is a semi-private API at the moment, but may be useful if you
dont want to change your model/manager.
'''
fieldname = _check_field_exists(model, fieldname)
instances = list(instances)
ids = [instance.pk for instance in instances]
field_object, model, direct, m2m = model._meta.get_field_by_name(fieldname)
if m2m:
if not direct:
m2m_field = field_object.field
related_model = field_object.model
related_name = m2m_field.name
id_column = m2m_field.m2m_reverse_name()
db_table = m2m_field.m2m_db_table()
else:
m2m_field = field_object
related_model = m2m_field.rel.to # model on other end of relationship
related_name = m2m_field.related_query_name()
id_column = m2m_field.m2m_column_name()
db_table = m2m_field.m2m_db_table()
elif not direct:
# handle reverse foreign key relationships
fk_field = field_object.field
related_model = field_object.model
related_name = fk_field.name
id_column = fk_field.column
db_table = related_model._meta.db_table
related_instances = _select_related_instances(related_model, related_name,
ids, db_table, id_column)
if filter:
related_instances = filter(related_instances)
grouped = {}
id_attr = _id_attr(id_column)
for related_instance in related_instances:
instance_id = getattr(related_instance, id_attr)
group = grouped.get(instance_id, [])
group.append(related_instance)
grouped[instance_id] = group
for instance in instances:
setattr(instance, target_field_name, grouped.get(instance.pk, []))
return instances
