Django - Getting last object created, simultaneous filters

Question

Apologies, I am completely new to Django and Python.

I have 2 questions. First, how would I go about getting the last object created (or highest pk) in a list of objects? For example, I know that I could use the following to get the first object:

list = List.objects.all()[0]

Is there a way to get the length of List.objects? I've tried List.objects.length but to no avail.

Second, is it possible to create simultaneous filters or combine lists? Here is an example:

def findNumber(request, number)
    phone_list = Numbers.objects.filter(cell=number)

I want something like the above, but more like:

def findNumber(request, number)
    phone_list = Numbers.objects.filter(cell=number or home_phone=number)

What is the correct syntax, if any?

score 82 · Accepted Answer · edited Jan 16 '18 at 20:59

I haven't tried this yet, but I'd look at the latest() operator on QuerySets:

latest(field_name=None)

Returns the latest object in the table, by date, using the field_name provided as the date field.

This example returns the latest Entry in the table, according to the pub_date field:

Entry.objects.latest('pub_date')

If your model's Meta specifies get_latest_by, you can leave off the field_name argument to latest(). Django will use the field specified in get_latest_by by default.

Like get(), latest() raises DoesNotExist if an object doesn't exist with the given parameters.

Note latest() exists purely for convenience and readability.

And the model docs on get_latest_by:

get_latest_by

Options.get_latest_by

The name of a DateField or DateTimeField in the model. This specifies the default field to use in your model Manager's latest method.

Example:

get_latest_by = "order_date"

See the docs for latest() for more.

Edit: Wade has a good answer on Q() operator.

Note that `.latest()` will raise a `DoesNotExist exception` if the queryset is empty - see [this answer](https://stackoverflow.com/questions/73297673/what-is-the-difference-between-queryset-last-and-latest-in-django). — Jakub Holan, May 20 '23 at 16:26

score 50 · Answer 2 · edited Aug 21 '15 at 15:43

50

this works!

Model.objects.latest('field') - field can be id. that will be the latest id

edited Aug 21 '15 at 15:43

Paul Richter

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answered Dec 11 '09 at 09:28

Harry

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Looks a bit like the answer I wrote four months before yours, no? – hughdbrown Oct 12 '10 at 18:52
20

Yours doesn't exactly inspire confidence with the _I haven't tried this yet_. This answer does. – duality_ Apr 17 '16 at 19:36
Does it raise conflict if there are more objects inserted at the dame date but at different times? (I mean, the date saved in DateField does bring hidden information about time?) – Tms91 Nov 08 '19 at 11:57
This is a good answer, as long as one doesn't use some random strings as id. – logicOnAbstractions Jul 13 '22 at 14:21

score 29 · Answer 3 · answered Nov 17 '15 at 16:41

29

Since Django 1.6 - last

last()

Works like first(), but returns the last object in the queryset.

Returns the last object matched by the queryset, or None if there is no matching object. If the QuerySet has no ordering defined, then the queryset is automatically ordered by the primary key.

list = List.objects.last() gives you the last object created

answered Nov 17 '15 at 16:41

punkrockpolly

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Important nuance: ordering can be defined not only directly in query, but in model's Meta as well - https://docs.djangoproject.com/en/3.2/ref/models/options/#ordering – Alexey Shrub Sep 06 '21 at 07:38

score 20 · Answer 4 · answered Aug 10 '09 at 19:58

20

For the largest primary key, try this:

List.objects.order_by('-pk')[0]

Note that using pk works regardless of the actual name of the field defined as your primary key.

answered Aug 10 '09 at 19:58

jcdyer

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score 4 · Answer 5 · answered Aug 10 '09 at 17:46

4

You can use the count() method on a query set the get the number of items.

list = List.objects.all()
list.count()

Arguments to filter are "AND"ed together. If you need to do OR filters look at Q objects. http://docs.djangoproject.com/en/dev/topics/db/queries/#complex-lookups-with-q-objects

answered Aug 10 '09 at 17:46

Wade

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Thanks, Wade! Just what I needed. – zdyn Aug 10 '09 at 18:04

score 0 · Answer 6 · answered Jul 23 '14 at 10:30

0

alternative for the latest object created:

List.objects.all()[List.objects.count()-1]

It is necessary to add an AssertionError for the case when there are no items in the list.

except AssertionError:
   ...

answered Jul 23 '14 at 10:30

RolandoAmir

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This will load all models from database. – wieczorek1990 Jul 22 '16 at 14:32

score 0 · Answer 7 · answered Feb 14 '18 at 08:13

I am working on Django version is 1.4.22, neither last nor lastet is working. My way to solve with minimum db loading is like:

latest = lambda model_objects, field : model_objects.values_list( field, flat = True ).order_by( "-" + field )[ 0 ]
latest_pk = latest( List.objects, "pk" )

This function accepts query_set as input.

You may bind this function dynamically by doing:

import types
List.objects.latest = types.MethodType( latest, List.objects )

Then you should be able to get the last object by this latest pk easily.

score 0 · Answer 8 · edited Jan 20 '22 at 20:20

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Try this:

InsertId= (TableName.objects.last()).id

edited Jan 20 '22 at 20:20

blackgreen

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answered Jan 20 '22 at 12:29

Merrin K

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Django - Getting last object created, simultaneous filters

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