10

I've got 2 questions, but they are related to the same topic.

I know how to retrieve data from a for loop using template tags

{% for status in status %}

    <tr>
        <td>{{ status.status}}</td>
    </tr>

{% endfor %}

However when I want to retrieve a single object i get an error even when i use:

po = Status.objects.latest('id')

and remove the for loop.

I get:

'Status' object is not iterable

My questions are:

  1. How can I get the latest entry from the database for a given model?
  2. How can I setup my templates tags to allow for just a single record?
Moe Far
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Jimmyn
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5 Answers5

22

You have two different questions here:

  1. How do I retrieve the latest object from the database.

You can do this using the latest() queryset operator. By reading the docs you will note that this operator works on date fields, not integers.

Status.objects.latest('date_added') # or date_updated

If you want to do this off the ID you will need to order by ID and select the first result. (this will only work if you are using incrementing primary keys, it will not work with UUID's or randomly generated hashes).

Status.objects.order_by('id')[0]

Side note: I would personally use the date_added / date_updated way of doing this.

  1. Iterating over a single object

A single object cannot be iterated over. For this you will need to use a different template. Or, you will need to add the single object into a list.

# note the [] around the query
result = [Status.object.latest('date_added')]

Personally I have a different views for listing single / multiple result. I have a ListView for many result objects and a DetailView for single objects.

Matt Seymour
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4
TableName.objects.filter(key=value).order_by('-date_filed').first()

The "-date_filed'" field will reverse the order and the first will give you the latest element.

ItsPete
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aijaz shekh
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2

Let us assume I have a Model named "OneOfTheModelsUsed" and there is a field called "car_name" and "date" within this model.

The following code worked for me while I was using Django FormWizard. After going through all the steps in the form and it gets saved. I used

last_entry = OneOfTheModelsUsed.objects.latest("date")

This gives all the entries in that model 

last_car_name = last_entry.car_name

This gives the specific field entry you want in the given form.

return render(request, 'reference.html', {'last_car_name':last_car_name,}

passed the data to a template.

for the display in the template I used 

{{last_car_model}}

and if you need the id for that entry.. use this {{last_car_model.id}} in the template.

PS:I'm fairly new to Django and Web development as a whole so I don't know much of the technical terms for all this

jrswgtr
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xyz
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1

This is because latest returns a single instance rather than a queryset (which is iterable). So:

1) Latest is not working because it works with Date Fields. Read more at: https://docs.djangoproject.com/en/1.8/ref/models/querysets/#latest. 'id' is not a valid field to use with the latest filter.

2) You can't use for template tag with a single instance because it is not iterable.

To solve your situation, I would specify the ordering = ('id',) field in the Meta class of the model and then do a po = Status.objects.all()[:1] so you will obtain a queryset (which is iterable) with a single object in it. Then you will be able to use the for template tag with your po variable.

Hope it helps.

argaen
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comments = usercomment.objects.order_by('-id')[:100]

I Did By This Method

First "comment" Is The Variable Name, "usercomment" Is Model Name, "id" is generated by django when make a model, [:100] is from 0 to 100 you can increase the number to x

Krishna Wadhwani
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