django-orm

问题 can someone ELI5 what CONN_MAX_AGE does? I thought it worked like this: 1) Request #1 comes in, opens connection 1 to database 2) Request #1 uses connection 1 to do some work 3) Request #1 completes. Because CONN_MAX_AGE is non-zero (and the age has not been reached), the connection is left open. 4) Request #2 comes in, and Django re-uses connection #1 to the database. But that doesn't seem to be happening. I have a page on my site that does an AJAX poll every 15 seconds. In my development

问题 In one celery task I need to create temporary table in database. In this article Daniel Roseman explained how to create one. But this solution does not work in Django 1.9. I tried to look into Django docs and Google but I was unable to find anything useful. Code from mentioned article which worked in Django 1.8: from django.db import models, cursor from django.contrib.contenttypes.management import update_contenttypes from django.core.management import call_command class TempCustomerAddress

问题 My model in Django ORM is this class Test(Modelbase): id = models.IntegerField(null=True, blank=True) amount = models.CharField(max_length=255) I want to add the amount for list of id's. The only problem is the amount field is CharField . How do I apply sum for the amount field? Test.objects.filter(id__in=[1,2,3]).aggregate(Sum('amount')) I am using Django=1.9.1 for this. 回答1: you can try do annotate with cast: from django.db.models import FloatField from django.db.models.functions import

问题 I want to create some part of Django ORM filter query dinamicly, now I can do: if some: Obj.filter( some_f1=some_v1, f1=v1, f2=v2, f3=v3, f4=v4, ... ) else: Obj.filter( f1=v1, f2=v2, f3=v3, f4=v4, ... ) I want something without code duplicate like this: Obj.filter( Q(some_f1=some_v1) if some else True, # what to use instead of True? f1=v1, f2=v2, f3=v3, f4=v4, ... ) 回答1: Here's a hacky way to get an always true Q object: always_true = ~Q(pk=None) This depends on the fact that the primary key

问题 I am trying to run an aggregation query that is roughly equals to: select sum(impressions) as impressions, sum(clicks) as clicks, sum(clicks)/sum(impressions) as ctr from stats group by product order by ctr; The database used is PostgreSQL. I made this query expression (Django 1.9): Stats.objects.values('product').annotate( impressions = models.Sum('impressions'), clicks = models.Sum('clicks'), ctr = models.ExpressionWrapper( models.F('clicks')/models.F('impressions')), output_field = models

问题 Here is what I'm trying to do: Make a model in Django that is a PostgreSQL array (database specific type), which contains foreign keys to another model. class Books(models.Model): authors = ArrayField( models.ForeignKey('my_app.Authors', default=None, null=True, blank=True), blank=True, default=list() ) When I try to makemigrations, Django gives me this error: SystemCheckError: System check identified some issues: ERRORS: my_app.Books.authors: (postgres.E002) Base field for array cannot be a

问题 I have the following models in my django project: class Video(models.Model): media = models.ForeignKey(Media) class Media(models.Model): title = models.CharField(max_length=255) formats = models.ManyToManyField(Format,through='MediaFormat',related_name='media',blank=True) class Format(models.Model): title = models.CharField(max_length=50) class MediaFormat(models.Model): status = models.IntegerField() format = models.ForeignKey(Format) media = models.ForeignKey(Media) Now, I want to filter

问题 Are the following two calls resolved to the equivalent SQL query in Django? Chaining multiple calls Model.objects \ .filter(arg1=foo) \ .filter(arg2=bar) \ ... Wrapping all the args together: Model.objects \ .filter(arg1=foo, arg2=bar) I'd like code to be readable (there are MANY more filter calls than I've shown), but only if there's no sacrifice to performance. 回答1: Update: Disregard this answer. See this better, correct answer. Thanks @Sam for the heads up. Old Answer: Are the following

问题 I have a Route model which should store an ordered list of stops along that route. How should I go about modeling this relation? class Stop(models.Model): name = .. latitude = .. longitude = .. class Route(models.Model): stops_list = # Ordered list of stops on the route 回答1: Since there are many Stops along a Route, and stops could belong to multiple routes, I would use a ManyToMany to store this relationship. You may specify a through model to store data about the relationship, such as what

问题 To clarify my question I would like to know if it is possible to idiomatically use the Django ORM whilst accessing CTE features. I imagine I could use CTE by writing raw SQL statements but the ability to use the ORM 'syntactic sugar' to bypass hand coding SQL statements was one of the original appeals of Django. 回答1: Django doesn't support CTEs directly as these are not common to all databases (MySQL doesn't support it). There are packages that extend the capability of Django's ORM to support