From fc511abac083fa57171ddd39b9ec6d410f4104ea Mon Sep 17 00:00:00 2001
From: Rohith Asrk <rohith.asrk@gmail.com>
Date: Fri, 17 Mar 2017 12:40:33 +0530
Subject: [PATCH] Fixes #96: Improve string representation of sortedm2m
 relationships

---
 README.rst                | 10 ++++++++++
 example/testapp/models.py |  8 +++++++-
 sortedm2m/fields.py       | 19 ++++++++++++++-----
 sortedm2m_tests/models.py |  8 +++++++-
 4 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/README.rst b/README.rst
index 3c95d19..18dbc20 100644
--- a/README.rst
+++ b/README.rst
@@ -77,6 +77,16 @@ Specifies how the field is called in the intermediate database table by which
 the relationship is ordered. You can change its name if you have a legacy
 database that you need to integrate into your application.
 
+``base_class``
+~~~~~~~~~~~~~~
+
+**Default:** ``None``
+
+You can set the ``base_class``, which is the base class of the through model of
+the sortedm2m relationship between models to an abstract base class containing
+a ``__str__`` method to improve the string representations of sortedm2m
+relationships.
+
 Migrating a ``ManyToManyField`` to be a ``SortedManyToManyField``
 =================================================================
 
diff --git a/example/testapp/models.py b/example/testapp/models.py
index 4e6848a..98a89ec 100644
--- a/example/testapp/models.py
+++ b/example/testapp/models.py
@@ -10,9 +10,15 @@ def __unicode__(self):
         return self.plate
 
 
+class m2mprint:
+
+    def __unicode__(self):
+        return unicode(self.car) + " in " + unicode(self.parkingarea)
+
+
 class ParkingArea(models.Model):
     name = models.CharField(max_length=50)
-    cars = SortedManyToManyField(Car)
+    cars = SortedManyToManyField(Car, base_class=m2mprint)
 
     def __unicode__(self):
         return self.name
diff --git a/sortedm2m/fields.py b/sortedm2m/fields.py
index a6a34b1..661ca9c 100644
--- a/sortedm2m/fields.py
+++ b/sortedm2m/fields.py
@@ -216,13 +216,19 @@ class SortedManyToManyField(_ManyToManyField):
     Accept a boolean ``sorted`` attribute which specifies if relation is
     ordered or not. Default is set to ``True``. If ``sorted`` is set to
     ``False`` the field will behave exactly like django's ``ManyToManyField``.
+ 
+    Accept a class ``base_class`` attribute which specifies the base class of 
+    the intermediate model. It allows to customize the intermediate model.
     '''
-    def __init__(self, to, sorted=True, **kwargs):
+    def __init__(self, to, sorted=True, base_class=None, **kwargs):
         self.sorted = sorted
         self.sort_value_field_name = kwargs.pop(
             'sort_value_field_name',
             SORT_VALUE_FIELD_NAME)
 
+        # Base class of through model  
+        self.base_class = base_class
+
         super(SortedManyToManyField, self).__init__(to, **kwargs)
         if self.sorted:
             self.help_text = kwargs.get('help_text', None)
@@ -376,16 +382,19 @@ def get_intermediate_model_to_field(self, klass):
 
     def create_intermediate_model_from_attrs(self, klass, attrs):
         name = self.get_intermediate_model_name(klass)
-        return type(str(name), (models.Model,), attrs)
+        base_classes = (models.Model, self.base_class) if self.base_class else (models.Model,)
+
+        return type(str(name), base_classes, attrs)
 
     def create_intermediate_model(self, klass):
         # Construct and return the new class.
         from_field_name, from_field = self.get_intermediate_model_from_field(klass)
         to_field_name, to_field = self.get_intermediate_model_to_field(klass)
         sort_value_field_name, sort_value_field = self.get_intermediate_model_sort_value_field(klass)
-
-        meta = self.get_intermediate_model_meta_class(
-            klass, from_field_name, to_field_name, sort_value_field_name)
+        meta = self.get_intermediate_model_meta_class(klass,
+                                                      from_field_name,
+                                                      to_field_name,
+                                                      sort_value_field_name)
 
         attrs = {
             'Meta': meta,
diff --git a/sortedm2m_tests/models.py b/sortedm2m_tests/models.py
index 170e8e0..f09cf69 100644
--- a/sortedm2m_tests/models.py
+++ b/sortedm2m_tests/models.py
@@ -3,8 +3,14 @@
 from sortedm2m.fields import SortedManyToManyField
 
 
+class m2mprint:
+
+    def __unicode__(self):
+        return unicode(self.book)
+
+
 class Shelf(models.Model):
-    books = SortedManyToManyField('Book', related_name='shelves')
+    books = SortedManyToManyField('Book', related_name='shelves', base_class=m2mprint)
 
 
 class Book(models.Model):