python - Custom lookup is not being registered in Django -

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i've created custom lookup. i'm using query, however, when so, error related field got invalid lookup: lcb thrown.

i'm assuming because custom lookup isn't being registered properly. you'll see below, i've tried several things , i'm lost issue is.

here's code:

tenants/views.py

from main.lookups import *  def find_tenants(request, house_id):     house = houselisting.objects.get(pk=house_id)     applications = housingapplication.objects.filter(date_from__gte=house.available_from)     applications = applications.filter(pets__lcb=house.allowed_pets.values_list('id', flat=true))      context = {'house': house, 'applications': applications}     return render(request, 'landlords/find-tenants.html', context)

main/lookups.py

from django.db.models import lookup, manytomanyfield   # custom lookups  @manytomanyfield.register_lookup class listcontainedby(lookup):     lookup_name = 'lcb'      def as_sql(self, compiler, connection):         lhs, lhs_params = self.process_lhs(compiler, connection)         rhs, rhs_params = self.process_rhs(compiler, connection)         params = lhs_params + rhs_params         return '%s <@ %s' % (lhs, rhs), params

i find strange, the docs suggest registering lookup in appconfig, or in models.py. i've tried both of these things , neither worked.

traceback

environment:   request method: request url: http://127.0.0.1:8000/landlords/find-tenants/5/  django version: 1.10.2 python version: 2.7.12 installed applications: ['main.apps.mainconfig',  'tenants.apps.tenantsconfig',  'landlords.apps.landlordsconfig',  'django.contrib.admin',  'django.contrib.auth',  'django.contrib.contenttypes',  'django.contrib.sessions',  'django.contrib.messages',  'django.contrib.staticfiles',  'django.contrib.humanize',  'django.contrib.postgres',  'imagekit'] installed middleware: ['django.middleware.security.securitymiddleware',  'django.contrib.sessions.middleware.sessionmiddleware',  'django.middleware.common.commonmiddleware',  'django.middleware.csrf.csrfviewmiddleware',  'django.contrib.auth.middleware.authenticationmiddleware',  'django.contrib.auth.middleware.sessionauthenticationmiddleware',  'django.contrib.messages.middleware.messagemiddleware',  'django.middleware.clickjacking.xframeoptionsmiddleware']    traceback:  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/core/handlers/exception.py" in inner   39.             response = get_response(request)  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/core/handlers/base.py" in _legacy_get_response   249.             response = self._get_response(request)  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/core/handlers/base.py" in _get_response   187.                 response = self.process_exception_by_middleware(e, request)  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/core/handlers/base.py" in _get_response   185.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/contrib/auth/decorators.py" in _wrapped_view   23.                 return view_func(request, *args, **kwargs)  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/contrib/auth/decorators.py" in _wrapped_view   23.                 return view_func(request, *args, **kwargs)  file "/users/mightyspaj/development/projects/housingfinder/housingfinder/landlords/views.py" in find_tenants   132.     applications = applications.filter(pets__lcb=house.allowed_pets.values_list('id', flat=true))  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/db/models/query.py" in filter   796.         return self._filter_or_exclude(false, *args, **kwargs)  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/db/models/query.py" in _filter_or_exclude   814.             clone.query.add_q(q(*args, **kwargs))  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/db/models/sql/query.py" in add_q   1227.         clause, _ = self._add_q(q_object, self.used_aliases)  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/db/models/sql/query.py" in _add_q   1253.                     allow_joins=allow_joins, split_subq=split_subq,  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/db/models/sql/query.py" in build_filter   1178.             lookup_class = field.get_lookup(lookups[0])  file "/users/mightyspaj/development/projects/housingfinder/lib/python2.7/site-packages/django/db/models/fields/related.py" in get_lookup   694.             raise typeerror('related field got invalid lookup: %s' % lookup_name)  exception type: typeerror @ /landlords/find-tenants/5/ exception value: related field got invalid lookup: lcb

all things i've tried far

  1. registering lookup in mainconfig.ready() function
  2. registering lookup in find_tenants() view
  3. registering lookup in main/models.py
  4. registering lookup field instead of manytomanyfield
  5. registering lookup using manytomanyfield.register_lookup() instead of decorator
  6. changing %s <@ %s %s = %s. thought issue might thinks sql invalid

edit 2

it looks of confusion might sorted out in later versions of django... edit 1 below 1.10, code different in tip perhaps has been fixed. try upgrading 1.11 , see if fixes it. options listed below still worth try if doesn't work.

edit 1

i realized misread exception in initial answer. actually, exception being hit 1 in django.db.models.fields.related.foreignobject.get_lookup, , code there clearer django not support custom lookups on relational fields:

class foreignobject(relatedfield):      ...      def get_lookup(self, lookup_name):         if lookup_name == 'in':             return relatedin         elif lookup_name == 'exact':             return relatedexact         elif lookup_name == 'gt':             return relatedgreaterthan         elif lookup_name == 'gte':             return relatedgreaterthanorequal         elif lookup_name == 'lt':             return relatedlessthan         elif lookup_name == 'lte':             return relatedlessthanorequal         elif lookup_name == 'isnull':             return relatedisnull         else:             raise typeerror('related field got invalid lookup: %s' % lookup_name)      ...

there are couple of things 1 thing try work though:

  1. implement custom lookup on 1 of fields through many many relationship, you'd have query like

    applications = applications.filter(     pets__id__lcb=house.allowed_pets.values_list('id', flat=true))

    i able along these lines work using in operator.

  2. alternatively, may able subclass foreignobject using , override get_lookup doesn't throw exception new operator... no doubt there bit of fiddle you'd have work though. edit: tried this, , didn't work because it's more complicated that, , join operation it's implicit field right-hand table field used, subclassing field left hand table not enough. option 1 seems right way go it.

original answer

i believe exception telling django won't attempt use custom lookups relational fields. given mention i'm guessing pets manytomanyfield, i.e. relational field, , guess lookup has been registered, django refusing use it.

the bit of code in django hitting (in django.db.models.sql.query.query.build_filter()) is:

.... if field.is_relation:     # no support transforms relational fields     num_lookups = len(lookups)     if num_lookups > 1:         raise fielderror('related field got invalid lookup: {}'.format(lookups[0])) ....

i can't understand rationale, explain why whatever mechanism tried use register lookup got same result.

it seems not-very-well documented issue. thing online find out (with 10 minutes searching) this, else came same conclusion.


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