# Creating a summary of objects

**URL:** <https://forum.djangoproject.com/t/creating-a-summary-of-objects/2017>\
**Category:** Using Django\
**Created:** [April 17, 2020, 3:11pm UTC](https://forum.djangoproject.com/t/creating-a-summary-of-objects/2017 "2020-04-17T15:11:17Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![bmtymrak](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/bmtymrak/32/1311_2.png) [@bmtymrak](https://forum.djangoproject.com/u/bmtymrak)\
**Post date:** [April 17, 2020, 3:11pm UTC](https://forum.djangoproject.com/t/creating-a-summary-of-objects/2017/1 "2020-04-17T15:11:17Z")

</div>

I’m trying to create a summary of objects from the following model:

```
 class Purchase(models.Model):
    item = models.CharField(max_length=250, blank=False)
    price = models.IntegerField()
    date = models.DateField()
    store = models.CharField(max_length=250, blank=True)
    location = models.CharField(max_length=250, blank=True)
    category = models.CharField(max_length=250, blank=False)
    subcategory = models.CharField(max_length=250, blank=True)
    notes = models.TextField(blank=True)
    purchaser = models.ForeignKey(
        get_user_model(),
        on_delete=models.CASCADE,
    )

    def __str__ (self):
        return self.item

    class Meta:
        ordering = ['-date']

```

I want the summary to show the total sum of the price of all purchases for a given category in a given month and given year. Something like

```
Year_1:
       Month_1:
               Category_1: Total
               Category_2: Total
Year_2:
       Month_2:
               Category_1: Total
               Category_2: Total
....

```

I am able to use annotate() to get a queryset via:

```
Purchase.objects.values('date __year', 'date__ month','category')
   .filter(purchaser__username='testuser')
   .annotate(total=Sum('price')).order_by()

```

which gives me the total sum for each category, but each category is in a separate dict for the same year and month.

```
QuerySet [
{'date __year': 2020, 'date__ month': 1, 'category': 'Category_1', 'total': 3000}, 
{'date __year': 2020, 'date__ month': 1, 'category': 'Category_2', 'total': 3500}]

```

Is there anyway to create a summary in the format I want through a queryset, or am I going to have to build it manually based on the queryset I have shown?

Making it manually seems like it would require a lot of iteration of the queryset which wouldn’t be efficient so I’m trying to avoid that but I can’t find another way to do it.

Thanks!

---

<div class="post-metadata">

**Author:** ![adamchainz](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/adamchainz/32/26_2.png) [@adamchainz](https://forum.djangoproject.com/u/adamchainz)\
**Post date:** [April 17, 2020, 3:56pm UTC](https://forum.djangoproject.com/t/creating-a-summary-of-objects/2017/2 "2020-04-17T15:56:28Z")

</div>

> [@bmtymrak](#):
>
> Making it manually seems like it would require a lot of iteration of the queryset which wouldn’t be efficient so I’m trying to avoid that but I can’t find another way to do it.

Once your data is in-memory, repeat iteration over it is quite efficient. Python and computers are fast! The slow bits in database queries are normally networking and disk reads. See [Latency Numbers Every Programmer Should Know](https://gist.github.com/jboner/2841832).

> [@bmtymrak](#):
>
> Is there anyway to create a summary in the format I want through a queryset, or am I going to have to build it manually based on the queryset I have shown?

As I understand, you want a dict of dicts of dicts. There’s no way to make a QuerySet return that, querysets only return lists.

I think you want something like (untested):

```python
from collections import defaultdict

qs = Purchase.objects...
data = defaultdict(lambda: defaultdict(dict))
for year, month, category, total in qs:
    data[year][month][category] = total

```

Using `defaultdict` is a neat trick to shortcut creating all those dicts.

---

<div class="post-metadata">

**Author:** ![bmtymrak](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.djangoproject.com/bmtymrak/32/1311_2.png) [@bmtymrak](https://forum.djangoproject.com/u/bmtymrak)\
**Post date:** [April 17, 2020, 8:11pm UTC](https://forum.djangoproject.com/t/creating-a-summary-of-objects/2017/3 "2020-04-17T20:11:41Z")

</div>

Thanks Adam!

I was thinking that I would have to execute the query multiple times during iteration, but clearly I was wrong.

Is there a good way to display this type of dict of dicts of dicts in the template besides just iterating through it in the template?

I got that method working after looping back through the data dictionary and setting  
`.default_factory = None` for each defaultdict. I’m trying to see if I can get the same result using regroup on the original queryset.