1 files changed, 80 insertions, 0 deletions
diff --git a/app/utils/next_prev.py b/app/utils/next_prev.py
new file mode 100644
index 0000000..766add1
--- /dev/null
+++ b/app/utils/next_prev.py
@@ -0,0 +1,80 @@
+# -*- coding: utf-8 -*-
+# from https://github.com/gregplaysguitar/django-next-prev/blob/master/next_prev.py
+
+from functools import partial
+
+from django.db import models
+
+if not locals().get('reduce'):
+    from functools import reduce
+
+__version__ = '1.0.1'
+VERSION = tuple(map(int, __version__.split('.')))
+
+
+def get_model_attr(instance, attr):
+    """Example usage: get_model_attr(instance, 'category__slug')"""
+    for field in attr.split('__'):
+        instance = getattr(instance, field)
+    return instance
+
+
+def next_or_prev_in_order(instance, qs=None, prev=False, loop=False):
+    """Get the next (or previous with prev=True) item for instance, from the
+       given queryset (which is assumed to contain instance) respecting
+       queryset ordering. If loop is True, return the first/last item when the
+       end/start is reached. """
+
+    if not qs:
+        qs = instance.__class__.objects.all()
+
+    if prev:
+        qs = qs.reverse()
+        lookup = 'lt'
+    else:
+        lookup = 'gt'
+
+    q_list = []
+    prev_fields = []
+
+    if qs.query.extra_order_by:
+        ordering = qs.query.extra_order_by
+    elif qs.query.order_by:
+        ordering = qs.query.order_by
+    elif qs.query.get_meta().ordering:
+        ordering = qs.query.get_meta().ordering
+    else:
+        ordering = []
+
+    ordering = list(ordering)
+
+    # if the ordering doesn't contain pk, append it and reorder the queryset
+    # to ensure consistency
+    if 'pk' not in ordering and '-pk' not in ordering:
+        ordering.append('pk')
+        qs = qs.order_by(*ordering)
+
+    for field in ordering:
+        if field[0] == '-':
+            this_lookup = (lookup == 'gt' and 'lt' or 'gt')
+            field = field[1:]
+        else:
+            this_lookup = lookup
+        q_kwargs = dict([(f, get_model_attr(instance, f))
+                         for f in prev_fields])
+        key = "%s__%s" % (field, this_lookup)
+        q_kwargs[key] = get_model_attr(instance, field)
+        q_list.append(models.Q(**q_kwargs))
+        prev_fields.append(field)
+    try:
+        return qs.filter(reduce(models.Q.__or__, q_list))[0]
+    except IndexError:
+        length = qs.count()
+        if loop and length > 1:
+            # queryset is reversed above if prev
+            return qs[0]
+    return None
+
+
+next_in_order = partial(next_or_prev_in_order, prev=False)
+prev_in_order = partial(next_or_prev_in_order, prev=True)