Added Many-to-Many Support

See jazzband#16

.gitignore

@@ -12,3 +12,4 @@ test_files/
 /.ve
 /.project
 /.pydevproject
+.idea/

simple_history/models.py

@@ -7,6 +7,7 @@
 from django.contrib import admin
 from django.utils import importlib
 from .manager import HistoryDescriptor
+from simple_history import register
 
 try:
     basestring
@@ -35,14 +36,16 @@ def python_2_unicode_compatible(klass):
 
 
 class HistoricalRecords(object):
-    def __init__(self, verbose_name=None):
+    def __init__(self, verbose_name=None, m2m_fields=None):
         self.user_set_verbose_name = verbose_name
+        self.m2m_fields = m2m_fields
 
     def contribute_to_class(self, cls, name):
         self.manager_name = name
         self.module = cls.__module__
         models.signals.class_prepared.connect(self.finalize, sender=cls)
         self.add_extra_methods(cls)
+        self.setup_m2m_history(cls)
 
     def add_extra_methods(self, cls):
         def save_without_historical_record(self, *args, **kwargs):
@@ -60,6 +63,17 @@ def save_without_historical_record(self, *args, **kwargs):
         setattr(cls, 'save_without_historical_record',
                 save_without_historical_record)
 
+    def setup_m2m_history(self, cls):
+        m2m_history_fields = self.m2m_fields
+        if m2m_history_fields:
+            assert (isinstance(m2m_history_fields, list) or isinstance(m2m_history_fields, tuple)), 'm2m_history_fields must be a list or tuple'
+            for field_name in m2m_history_fields:
+                field = getattr(cls, field_name).field
+                assert isinstance(field, models.fields.related.ManyToManyField), ('%s must be a ManyToManyField' % field_name)
+                if not sum([isinstance(item, HistoricalRecords) for item in field.rel.through.__dict__.values()]):
+                    field.rel.through.history = HistoricalRecords()
+                    register(field.rel.through)
+
     def finalize(self, sender, **kwargs):
         history_model = self.create_history_model(sender)
         module = importlib.import_module(self.module)
@@ -71,6 +85,7 @@ def finalize(self, sender, **kwargs):
                                          weak=False)
         models.signals.post_delete.connect(self.post_delete, sender=sender,
                                            weak=False)
+        models.signals.m2m_changed.connect(self.m2m_changed, sender=sender, weak=False)
 
         descriptor = HistoryDescriptor(history_model)
         setattr(sender, self.manager_name, descriptor)
@@ -177,6 +192,27 @@ def post_save(self, instance, created, **kwargs):
     def post_delete(self, instance, **kwargs):
         self.create_historical_record(instance, '-')
 
+    def m2m_changed(self, action, instance, sender, **kwargs):
+        source_field_name, target_field_name = None, None
+        for field_name, field_value in sender.__dict__.items():
+            if isinstance(field_value, models.fields.related.ReverseSingleRelatedObjectDescriptor):
+                if field_value.field.related.parent_model == kwargs['model']:
+                    target_field_name = field_name
+                elif field_value.field.related.parent_model == type(instance):
+                    source_field_name = field_name
+        items = sender.objects.filter(**{source_field_name:instance})
+        if kwargs['pk_set']:
+            items = items.filter(**{target_field_name + '__id__in':kwargs['pk_set']})
+        for item in items:
+            if action == 'post_add':
+                if hasattr(item, 'skip_history_when_saving'):
+                    return
+                self.create_historical_record(item, '+')
+            elif action == 'pre_remove':
+                self.create_historical_record(item, '-')
+            elif action == 'pre_clear':
+                self.create_historical_record(item, '-')
+
     def create_historical_record(self, instance, type):
         history_user = getattr(instance, '_history_user', None)
         manager = getattr(instance, self.manager_name)