Improve REST mixins and add a new one

Add type casting to ExternalObjectListSerializerMixin via
the external_object_list_pk_type option.

Add an ExternalObjectSerializeMixin for related objects.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/rest_api/mixins.py

@@ -2,6 +2,7 @@ from __future__ import absolute_import, unicode_literals
 
 from django.core.exceptions import ImproperlyConfigured
 
+from rest_framework.exceptions import ValidationError
 from rest_framework.settings import api_settings
 
 from mayan.apps.acls.models import AccessControlList
@@ -16,6 +17,7 @@ class ExternalObjectListSerializerMixin(object):
         external_object_list_queryset
         external_object_list_pk_field
         external_object_list_pk_list_field
+        external_object_list_pk_type
 
     The source queryset can also be provided overriding the
     .get_external_object_list_queryset() method.
@@ -23,14 +25,24 @@ class ExternalObjectListSerializerMixin(object):
     def __init__(self, *args, **kwargs):
         super(ExternalObjectListSerializerMixin, self).__init__(*args, **kwargs)
         self.external_object_list_options = getattr(self, 'Meta', None)
+        self.external_object_list_options_defaults = {
+            'external_object_list_pk_type': int
+        }
+
+    def filter_queryset(self, id_list, queryset):
+        """
+        Allow customizing the final filtering, used for object lists that are
+        not a queryset like the Permission class.
+        """
+        return queryset.filter(pk__in=id_list)
 
     def get_external_object_list(self):
         queryset = self.get_external_object_list_queryset()
 
-        if self.Meta.external_object_list_permission:
+        permission = self.get_external_object_list_option('permission')
+        if permission:
             queryset = AccessControlList.objects.restrict_queryset(
-                permission=self.Meta.external_object_list_permission,
-                queryset=queryset,
+                permission=permission, queryset=queryset,
                 user=self.context['request'].user
             )
 
@@ -40,7 +52,7 @@ class ExternalObjectListSerializerMixin(object):
         if not pk_field and not pk_list_field:
             raise ImproperlyConfigured(
                 'ExternalObjectListSerializerMixin requires a '
-                'external_object_list_pk_field a '
+                'external_object_list_pk_field or a'
                 'external_object_list_pk_list_field.'
             )
 
@@ -61,12 +73,33 @@ class ExternalObjectListSerializerMixin(object):
         else:
             id_list = ()
 
-        return queryset.filter(pk__in=id_list)
+        pk_type = self.get_external_object_list_option('pk_type')
+
+        if pk_type:
+            result = []
+
+            for pk in id_list:
+                try:
+                    result.append(pk_type(pk))
+                except Exception as exception:
+                    raise ValidationError(
+                        {
+                            api_settings.NON_FIELD_ERRORS_KEY: [
+                                'Value "{}" is not of a valid type; {}'.format(pk, exception)
+                            ]
+                        }, code='invalid'
+                    )
+
+            id_list = result
+
+        return self.filter_queryset(id_list=id_list, queryset=queryset)
 
     def get_external_object_list_option(self, option_name):
+        full_option_name = 'external_object_list_{}'.format(option_name)
+
         return getattr(
-            self.external_object_list_options, 'external_object_list_{}'.format(option_name),
-            None
+            self.external_object_list_options, full_option_name,
+            self.external_object_list_options_defaults.get(full_option_name)
         )
 
     def get_external_object_list_queryset(self):
@@ -86,6 +119,82 @@ class ExternalObjectListSerializerMixin(object):
         return queryset
 
 
+class ExternalObjectSerializerMixin(object):
+    """
+    Mixin to allow serializers to get a restricted object with minimal code.
+    This mixin adds the follow class Meta options to a serializer:
+        external_object_model
+        external_object_permission
+        external_object_queryset
+        external_object_pk_field
+    The source queryset can also be provided overriding the
+    .get_external_object_queryset() method.
+    """
+    def __init__(self, *args, **kwargs):
+        super(ExternalObjectSerializerMixin, self).__init__(*args, **kwargs)
+        self.external_object_options = getattr(self, 'Meta', None)
+
+    def get_external_object(self):
+        queryset = self.get_external_object_queryset()
+
+        permission = self.get_external_object_permission()
+        if permission:
+            queryset = AccessControlList.objects.restrict_queryset(
+                permission=permission, queryset=queryset,
+                user=self.context['request'].user
+            )
+
+        pk_field = self.get_external_object_option('pk_field')
+
+        if not pk_field:
+            raise ImproperlyConfigured(
+                'ExternalObjectSerializerMixin requires a '
+                'external_object_pk_field.'
+            )
+
+        if pk_field:
+            pk_field_value = self.validated_data.get(pk_field)
+        else:
+            pk_field_value = None
+
+        if pk_field_value:
+            try:
+                return queryset.get(pk=pk_field_value)
+            except Exception as exception:
+                raise ValidationError(
+                    {
+                        pk_field: [exception]
+                    }, code='invalid'
+                )
+
+    def get_external_object_option(self, option_name):
+        full_option_name = 'external_object_{}'.format(option_name)
+
+        return getattr(
+            self.external_object_options, full_option_name,
+            None
+        )
+
+    def get_external_object_permission(self):
+        return self.get_external_object_option('permission')
+
+    def get_external_object_queryset(self):
+        model = self.get_external_object_option('model')
+        queryset = self.get_external_object_option('queryset')
+
+        if model:
+            queryset = model._meta.default_manager.all()
+        elif queryset:
+            return queryset
+        else:
+            raise ImproperlyConfigured(
+                'ExternalObjectListSerializerMixin requires a '
+                'external_object_model or a external_object_queryset.'
+            )
+
+        return queryset
+
+
 class SuccessHeadersMixin(object):
     def get_success_headers(self, data):
         try: