Django values_list vs values

Question

In Django, what's the difference between the following two:

Article.objects.values_list('comment_id', flat=True).distinct()

versus:

Article.objects.values('comment_id').distinct()

My goal is to get a list of unique comment ids under each Article. I've read the documentation (and in fact have used both approaches). The results overtly seem similar.

With values_list you can do `if self.id in Article.objects.values_list('comment_id', flat=True):` while using values you need to access the dictionary — dnaranjo, May 13 '16 at 09:20
@dnaranjo - You could but why not just do `Article.objects.filter(comment_id=self.id).exists()`? — Sayse, May 13 '16 at 09:34

Alasdair · Accepted Answer · 2020-12-10T10:40:35.400

474

The values() method returns a QuerySet containing dictionaries:

<QuerySet [{'comment_id': 1}, {'comment_id': 2}]>

The values_list() method returns a QuerySet containing tuples:

<QuerySet [(1,), (2,)]>

If you are using values_list() with a single field, you can use flat=True to return a QuerySet of single values instead of 1-tuples:

<QuerySet [1, 2]>

edited Dec 10 '20 at 10:40

answered May 13 '16 at 09:13

Alasdair

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Oh and no difference among the two vis-a-vis how `distinct()` is used huh? – Hassan Baig May 13 '16 at 09:16
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No, I don't think `distinct()` works any differently. The important thing is which data structure that you want to work with. – Alasdair May 13 '16 at 09:18
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The `values()` returns a `QuerySet` and not a `list`. Although the object returned by `values()` looks like a `list`, it doesn't behave like one in some cases. For example, it won't be json serializable unless we convert it into a `list' – Abhijit Ghate Aug 07 '18 at 11:57
@AbhijitGhate good point, I've updated the answer to make that clearer. – Alasdair Aug 07 '18 at 12:20
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You can easily convert the return from `values_list` to a true Python list by just using the `list` function: `list(Article.objects.values_list('comment_id', flat=True).distinct())` – inostia May 13 '19 at 23:08
As mentioned, if your tuple has 1 value then you can use `flat=True`. But if it has 2 values such as `[('name', 'Jim')]` you can use `dict(`[('name', 'Jim')]`)` which converts it to a dictionary with key-value pairs: `{'name': 'Jim'}`. Very useful. – enchance Feb 16 '20 at 16:08
@inostia In Django 2.2 I get "Error in argument:" when trying to convert using `list()` – l0b0 Jun 18 '20 at 06:24
@l0b0 the issue is probably in the queryset itself, not the `list()` call. We can’t help with that in the comments here. If you’re still sick please open a new question and include the code, models and full traceback of the error. – Alasdair Jun 18 '20 at 08:14
Turns out `set()` does work, so I'm just using that. – l0b0 Jun 18 '20 at 09:22

score 104 · Answer 2 · edited Dec 09 '20 at 10:42

104

values()

Returns a QuerySet that returns dictionaries, rather than model instances, when used as an iterable.

values_list()

Returns a QuerySet that returns list of tuples, rather than model instances, when used as an iterable.

distinct()

distinct are used to eliminate the duplicate elements.

Example:

>>> list(Article.objects.values_list('id', flat=True)) # flat=True will remove the tuples and return the list   
[1, 2, 3, 4, 5, 6]

>>> list(Article.objects.values('id'))
[{'id':1}, {'id':2}, {'id':3}, {'id':4}, {'id':5}, {'id':6}]

edited Dec 09 '20 at 10:42

Flimm

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answered Dec 11 '16 at 10:50

Ibrahim Kasim

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So it's a list of dictionaries that's returned in case of `values` – Hassan Baig Dec 11 '16 at 16:27
2

Just to clarify: `distinct()` eliminates the duplicate elements from query results, not from database. – oz19 Dec 22 '19 at 17:10
Useful for those that use **MYSQL** because `distinct()` not allowed with this DB type – Abpostman1 Mar 31 '23 at 09:14

score 8 · Answer 3 · edited Feb 09 '23 at 05:43

"values()" returns a QuerySet of dictionaries.

For example:

print(User.objects.all().values()) # Return all fields
# <QuerySet [{'id': 1, 'name': 'John'}, {'id': 2, 'name': 'Tom'}]>

print(User.objects.all().values("name")) # Return "name" field
# <QuerySet [{'name': 'John'}, {'name': 'Tom'}]>

"values_list()" returns a QuerySet of tuples.

For example:

print(User.objects.all().values_list()) # Return all fields
# <QuerySet [(1, 'John'), (2, 'Tom')]>

print(User.objects.all().values_list("name")) # Return "name" field
# <QuerySet [('John',), ('Tom',)]>

"values_list()" with "flat=True" returns a QuerySet of values. *No or One field with "flat=True" is allowed and one field must be the 1st argument with "flat=True" which must be the 2nd argument.

For example:

print(User.objects.all().values_list(flat=True)) # Return "id" field
# <QuerySet [1, 2]>

print(User.objects.all().values_list("name", flat=True)) # Return "name" field
# <QuerySet ['John', 'Tom']>

print(User.objects.all().values_list(flat=True, "name")) # Error

print(User.objects.all().values_list("id", "name", flat=True)) # Error

score 5 · Answer 4 · edited Aug 11 '18 at 08:59

5

You can get the different values with:

set(Article.objects.values_list('comment_id', flat=True))

edited Aug 11 '18 at 08:59

glennsl

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answered Aug 10 '18 at 23:56

pitu

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This will be way slower than using `distinct()` to eliminate duplicates at database level. – Alexander Suraphel Aug 29 '20 at 15:11
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Also, using set() will force a query on the whole table, when a QuerySet (returned by `distinct()`) will stream data only when needed. – Elektordi Mar 22 '21 at 20:55

score 1 · Answer 5 · answered Nov 11 '20 at 12:00

The best place to understand the difference is at the official documentation on values / values_list. It has many useful examples and explains it very clearly. The django docs are very user freindly.

Here's a short snippet to keep SO reviewers happy:

values

Returns a QuerySet that returns dictionaries, rather than model instances, when used as an iterable.

And read the section which follows it:

value_list

This is similar to values() except that instead of returning dictionaries, it returns tuples when iterated over.

Django values_list vs values

5 Answers5

values()

values_list()

distinct()

values

value_list

Linked

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