def resolve_field(model_field, lookup_expr):
"""
Resolves a ``lookup_expr`` into its final output field, given
the initial ``model_field``. The lookup expression should only contain
transforms and lookups, not intermediary model field parts.
Note:
This method is based on django.db.models.sql.query.Query.build_lookup
For more info on the lookup API:
https://docs.djangoproject.com/en/1.9/ref/models/lookups/
"""
query = model_field.model._default_manager.all().query
lhs = Expression(model_field)
lookups = lookup_expr.split(LOOKUP_SEP)
assert len(lookups) > 0
while lookups:
name = lookups[0]
# If there is just one part left, try first get_lookup() so
# that if the lhs supports both transform and lookup for the
# name, then lookup will be picked.
if len(lookups) == 1:
final_lookup = lhs.get_lookup(name)
if not final_lookup:
# We didn't find a lookup. We are going to interpret
# the name as transform, and do an Exact lookup against
# it.
lhs = query.try_transform(lhs, name, lookups)
final_lookup = lhs.get_lookup('exact')
return lhs.output_field, final_lookup.lookup_name
lhs = query.try_transform(lhs, name, lookups)
lookups = lookups[1:]
def lookups_for_field(model_field):
"""
Generates a list of all possible lookup expressions for a model field.
"""
lookups = []
for expr, lookup in model_field.get_lookups().items():
if issubclass(lookup, Transform):
transform = lookup(Expression(model_field))
lookups += [
LOOKUP_SEP.join([expr, sub_expr]) for sub_expr
in lookups_for_transform(transform)
]
else:
lookups.append(expr)
return lookups
def lookups_for_field(model_field):
"""
Generates a list of all possible lookup expressions for a model field.
"""
# This is a hack to work around:
# https://github.com/django/django/pull/6906
if isinstance(model_field, ForeignObject):
return ['exact', 'gt', 'gte', 'lt', 'lte', 'in', 'isnull']
lookups = []
for expr, lookup in six.iteritems(class_lookups(model_field)):
if issubclass(lookup, Transform) and django.VERSION >= (1, 9):
transform = lookup(Expression(model_field))
lookups += [
LOOKUP_SEP.join([expr, sub_expr]) for sub_expr
in lookups_for_transform(transform)
]
else:
lookups.append(expr)
return lookups