Rely on Django to resolve string references in ForeignKey fields. Refs …

…#243

this commit tries to load & configure Django and use its internal machinery to resolve apps and models in case they are referenced as a string. If this fails it falls back to appending ".models" to the first part of the name and looking for a module with that name to augment.

pylint_django/tests/input/func_noerror_string_foreignkey.py

@@ -0,0 +1,11 @@
+"""
+Checks that PyLint correctly handles string foreign keys
+https://github.com/PyCQA/pylint-django/issues/243
+"""
+#  pylint: disable=missing-docstring
+from django.db import models
+
+
+class Book(models.Model):
+    author = models.ForeignKey("test_app.Author", models.CASCADE)
+    user = models.ForeignKey("auth.User", models.PROTECT)

pylint_django/tests/input/models/author.py

@@ -3,4 +3,5 @@
 
 
 class Author(models.Model):
-    pass
+    class Meta:
+        app_label = 'test_app'

pylint_django/tests/input/test_app/apps.py

@@ -0,0 +1,5 @@
+from django.apps import AppConfig
+
+
+class TestAppConfig(AppConfig):
+    name = 'test_app'

pylint_django/tests/input/test_app/models.py

@@ -0,0 +1 @@
+from models.author import Author  # noqa: F401

pylint_django/tests/settings.py

@@ -0,0 +1,12 @@
+SECRET_KEY = 'fake-key'
+
+INSTALLED_APPS = [
+    'django.contrib.auth',
+    'django.contrib.contenttypes',
+    'test_app',
+]
+
+MIDDLEWARE = [
+    'django.contrib.sessions.middleware.SessionMiddleware',
+    'django.contrib.auth.middleware.AuthenticationMiddleware',
+]

pylint_django/tests/test_func.py

@@ -6,6 +6,8 @@
 import pylint
 
 
+os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'pylint_django.tests.settings')
+
 try:
     # pylint 2.5: test_functional has been moved to pylint.testutils
     from pylint.testutils import FunctionalTestFile, LintModuleTest

pylint_django/transforms/foreignkey.py

@@ -41,6 +41,17 @@ def _get_model_class_defs_from_module(module, model_name, module_name):
     return class_defs
 
 
+def _module_name_from_django_model_resolution(model_name, module_name):
+    import django  # pylint: disable=import-outside-toplevel
+    django.setup()
+    from django.apps import apps  # pylint: disable=import-outside-toplevel
+
+    app = apps.get_app_config(module_name)
+    model = app.get_model(model_name)
+
+    return model.__module__
+
+
 def infer_key_classes(node, context=None):
     keyword_args = []
     if node.keywords:
@@ -87,10 +98,15 @@ def infer_key_classes(node, context=None):
                 module_name = current_module.name
             elif not module_name.endswith('models'):
                 # otherwise Django allows specifying an app name first, e.g.
-                # ForeignKey('auth.User') so we try to convert that to
-                # 'auth.models', 'User' which works nicely with the `endswith()`
-                # comparison below
-                module_name += '.models'
+                # ForeignKey('auth.User')
+                try:
+                    module_name = _module_name_from_django_model_resolution(model_name, module_name)
+                except LookupError:
+                    # If Django's model resolution fails we try to convert that to
+                    # 'auth.models', 'User' which works nicely with the `endswith()`
+                    # comparison below
+                    module_name += '.models'
+
                 # ensure that module is loaded in astroid_cache, for cases when models is a package
                 if module_name not in MANAGER.astroid_cache:
                     MANAGER.ast_from_module_name(module_name)