Riješeno: django označi polje datuma i vremena u char

Glavni problem je što django annotate datetime field to char neće raditi sa određenim datetime poljima. Na primjer, ako imate polje pod nazivom “created_at” i pokušate ga označiti klasom CharField, django vam neće dozvoliti da sačuvate svoje podatke.

field

I have a model with a datetime field and I want to annotate it to a charfield. I tried this:
<code>MyModel.objects.values('date').annotate(date_char=CharField())
</code>
but it gives me an error: <code>Cannot resolve keyword 'CharField' into field.</code>


A:

You can use <code>Func</code>:  https://docs.djangoproject.com/en/dev/ref/models/expressions/#func-expressions  and then use the <code>.format()</code> method on the resulting string to format it however you want (e.g., YYYY-MM-DD):   https://docs.python.org/2/library/string.html#formatstrings  .  Something like this should work:  
<code>from django.db import models     # for Func expression class   
from django import db           # for connection alias, used in Func expression class   

                                # create connection alias, used in Func expression class   

                                # (this is only necessary if you are using multiple databases)   

                                # replace 'default' with your database name if using multiple databases   

my_conn = db._connections['default']    

                                # create Func expression object that will convert date to string format YYYY-MM-DD    

my_func = models.Func(my_conn, function='TO_CHAR', template='%(function)s(%(expressions)s::DATE, 'YYYY-MM-DD')')    

                                # use my_func in query as follows:    

MyModelObjects = MyModelObjects .objects .values('date') .annotate(date_char=my_func)     
</code>

Datum i vrijeme u Djangu

Django pruža zgodan tip datuma i vremena koji se može koristiti za predstavljanje datuma i vremena.

Za kreiranje objekta datetime koristite konstruktor datetime:

>>> iz django.utils.datetime import datetime >>> d = datetime(2015, 11, 25) >>> d 2015-11-25 00:00:00

Primjeri datuma i vremena koda

Slijedi lista primjera datuma i vremena koda u Djangu.

iz django.utils.datetime import datetime iz django.utils.translation import gettext_lazy kao _ iz django.core.urlresolvers uvoz obrnuto iz django.db import modela klase User(models.Model): first_name = models.CharField(max_length=30, blank=Tačno, nullable=False) prezime = modeli.CharField(max_length=30, blank=Tačno, nullable=False) email = modeli.EmailField() def __str__(self): vrati self._first_name + ' ' + self._last_ + '@' + self._email