I have a Django website with activities. When checking for optimisation opportunities with the django-toolbar, I discovered that the view for an activity's subscription list was really inefficient. It made five database request per subscription, just to check if the user is a member.
My models are structured as follows:
class Subscription(models.Model):
user = models.ForeignKey(User, null=True)
activity = models.ForeignKey(Activity)
class MemberProfile(models.Model):
user = models.ForeignKey(User)
member_in = models.ManyToManyField(WorkYear, blank=True, null=True)
class WorkYear(models.Model):
year = models.SmallIntegerField(unique=True)
current = models.BooleanField(default=False, blank=True)
Now, to check if the subscribed user is a member, we must check if there's a MemberProfile referring to it, with a WorkYear in its member_in field with current set to true.
I had a property in Subscription called is_member which returned this information. In the template this property was called for every subscription, resulting in a massive amount of database requests.
Instead of doing this, I would like to add a custom field to the QuerySet created in the view.
I've experimented with the extra() function:
subscriptions = activity.subscription_set.extra(
select={
'is_member': 'SELECT current FROM activities_subscription LEFT OUTER JOIN (auth_user LEFT OUTER JOIN (members_memberprofile LEFT OUTER JOIN (members_memberprofile_member_in LEFT OUTER JOIN site_main_workyear ON members_memberprofile_member_in.workyear_id = site_main_workyear.id AND site_main_workyear.current = 1) ON members_memberprofile.id = members_memberprofile_member_in.memberprofile_id) ON auth_user.id = members_memberprofile.user_id) ON activities_subscription.user_id = auth_user.id'
},
tables=['site_main_workyear', 'members_memberprofile_member_in', 'members_memberprofile', 'auth_user']
).order_by('id')
This is really complex and for some reason it doesn't work. After reloading the page, Python takes 100% CPU and no response is given.
Is there a better and more simple way for doing this? And if not, what am I doing wrong?
Related
I am new to django. I have a model like this:
class Standup(models.Model):
team = models.ForeignKey("Team", on_delete=models.CASCADE)
standup_time = models.DateTimeField(auto_now_add=True)
class StandupUpdate(models.Model):
standup = models.ForeignKey("Standup", on_delete=models.CASCADE)
employee = models.ForeignKey("Employee", on_delete=models.CASCADE)
update_time = models.DateTimeField(auto_now_add=True)
status = models.CharField(max_length=50)
work_done_yesterday = models.TextField()
work_to_do = models.TextField()
blockers = models.TextField()
If I write view for this model, every employee will have to hit API for his/her standup update. But I am supposed create a single API which takes updates of all the employees and saves it into database. In frontend, it will be something like this:
Employee will select on a team as one employee can be a part of
multiple teams.
Then the employee will give his/her stadup updates.
Then another employee will do the same thing and so on.
At the end,by clicking on submit button, whole data will be saved together.
Any guidance on how to do it?
Not sure why you need a separate model for Updates.
I would try to approach it like that:
make the Standup model reference both Team and Employee models;
last_update, status, work_to_do etc. as its fields;
make a custom serializer that accepts a list with Standup field values and takes the authorized user's ID from request object's data. last_update time can be now(), status calculated according to your business logic
This part of DRF documentation could probably be helpful.
The following is in my models.py:
class SensorType(models.Model):
hardware_type = models.CharField(max_length=100)
is_static = models.BooleanField(default=False)
# Some other fields
class Sensor(models.Model):
device_id = models.CharField(max_length=100, primary_key=True)
sensor_type = models.ForeignKey(SensorType, on_delete=models.PROTECT)
# Some other fields
class Asset(models.Model):
name = models.CharField(max_length=100)
sensor_type = models.ForeignKey(SensorType, on_delete=models.PROTECT) # I need to use this field to filter below
sensor = models.ForeignKey(Sensor, on_delete=models.PROTECT, limit_choices_to={'sensor_type': WHAT DO I PUT HERE?},)
# Some other fields
I need to limit the choices in the sensor field of asset so that only sensors with the sensor_type set in the field immediately above, show up.
The reasoning behind this is that there will eventually be many sensors and it would be very useful to filter this. Initially I only need this to work from the admin page but this will eventually extend when I make my Create and Update Views.
Is this even possible? I'm essentially trying to access attributes before the object has actually been created.
After reading several other questions such as this one I have also looked into ModelChoiceField but the same issue exists of trying to access the form data before it has been submitted.
I'm very open to changing the model structure if that is what is required.
I have the following two models:
class URLResource(models.Model):
class ResourceType(models.TextChoices):
VID = 'VID', _('Video')
DOC = 'DOC', _('Document')
resource_type = models.CharField(
choices=ResourceType.choices,
default=ResourceType.UNK,
max_length=3)
title = models.CharField(max_length=280, null=True)
url = models.URLField()
created = models.DateTimeField(auto_now_add=True)
def __repr__(self):
return f'URLResource {self.resource_type}: {self.title} URL: {self.url}'
class Record(models.Model):
user = models.ForeignKey(
settings.AUTH_USER_MODEL,
...)
date = models.DateTimeField(default=now, blank=True)
# <resource>: I want to point to a resource somehow
def __repr__(self):
return f'Record {{ User: {self.user}, Resource: }}'
My use case is such that a lot of users can create Records and list them, but since the underlying URLResource is going to be same, I thought I could use many-to-one relationship from Records-to-URLResource so the underlying resources would remain the same. However, even though I have only one type of resource now i.e. URLResource, I also want to roll out other resources like VideoResource, PhysicalResource etc. Clearly, I can't simply use the many-to-one relationship. So, I figured I could use Django's contenttype framework, but I still can't get things to work.
I want to be able to do atleast these two things:
When creating a Record, I can easily assign it a URLResource (or any other Resource) (but only one resource).
I can easily access the URLResource fields. For example like Record.objects.get(user=x).resource.resource_type.
Question / Problem:
I am building a Django app, with 2 models: User and Secret. Secrets can be made by Users, and other Users can "like" them. I've setup my likes field as a ManyToManyField, so that Users whom like a Secret can be stored there and later retrieved, etc. However, when I try to query for a User and a Secret and use my_secret.likes.add(my_User) nothing happens. I don't receive an error and when I print my Secret's many-to-many likes field, after the add, I see: secrets.User.None.
Why is my add() method running but I am not receiving any errors, and why is my User not properly being added to my Secret's likes?
Note: I've saved both the User and Secret objects upon initial creation. Outside this application I've been able to use the add() method just fine, but in those scenarios I was creating objects in the moment, and not retreiving already existing objects.
Is there a different way to handle add() when using data retreived from a Query? That's my only other line of reasoning right now, and I've followed the documentation here exactly: Django Many-to-Many Docs
I also apologize if this was answered elsewhere on the site. I did find one other post here, but there was no solution provided, granted they were experiencing the exact same issue.
My Models:
class User(models.Model):
"""
Creates instances of a `User`.
Parameters:
-`models.Model` - Django's `models.Model` method allows us to create new models.
"""
first_name = models.CharField(max_length=50) # CharField is field type for characters
last_name = models.CharField(max_length=50)
email = models.CharField(max_length=50)
password = models.CharField(max_length=22)
created_at = models.DateTimeField(auto_now_add=True) # DateTimeField is field type for date and time
updated_at = models.DateTimeField(auto_now=True) # note the `auto_now=True` parameter
objects = UserManager() # Attaches `UserManager` methods to our `User.objects` object.
class Secret(models.Model):
"""
Creates instances of a `Secret`.
Parameters:
-`models.Model` - Django's `models.Model` method allows us to create new models.
"""
description = models.CharField(max_length=100) # CharField is field type for characters
user = models.ForeignKey(User, related_name="secrets") # One-to-Many Relationship
likes = models.ManyToManyField(User) # Many to Many Relationship
created_at = models.DateTimeField(auto_now_add=True) # DateTimeField is field type for date and time
updated_at = models.DateTimeField(auto_now=True) # note the `auto_now=True` parameter
objects = SecretManager() # Attaches `SecretManager` methods to our `Secret.objects` object.
Problem Example:
The model migrates fine, everything seems to be in proper syntax. However, when I try and retrieve a User and a Secret, and add the User to the Secret.likes, the add() method gives no errors, runs, but no objects are saved.
Here's an example:
tim = User.objects.get(email="tim#tim.com") # Gets a user object
my_secret = Secret.objects.get(id=2) # Gets a secret object
# This is where nothing seems to happen / take:
my_secret.likes.add(tim) # add() method per Django many-to-many docs
print my_secret.likes # returns: `secrets.User.None` -- why?
Why when printing my_secret.likes above, is nothing printed?
Especially when:
tim.secret_set.all() shows the secret containing an id=2 as in the above example....so the User is recording the relationship with the Secret, but the Secret is not recording any relationship with the User. What am I doing wrong?
You need to call the all method of the many-to-many field to view all related objects:
print my_secret.likes.all()
# ^^^^^
I have a live web-based chat app made in Django. Users can form groups where other users can congregate, leave messages (called replies) and photos. The url every user visits to access a group is:
url(r'^group/(?P<pk>\d+)/reply/$', auth(GroupView.as_view()), name="group_reply"),
where pk is group.pk.
My question is: how can I get a list (or set) of all distinct users who accessed a certain group's URL in the last 5 mins? Essentially, I'm trying to calculate the number of unique recent visitors for each group. I can't seem to wrap my head around how to do this, though I guess sessions information could help? (I'm using django user_sessions in this project, which
"makes session objects a first class citizen like other ORM objects"
).
In case required, the model behind a group is:
class Group(models.Model):
topic = models.TextField(validators=[MaxLengthValidator(200)], null=True)
rules = models.TextField(validators=[MaxLengthValidator(500)], null=True)
owner = models.ForeignKey(User)
private = models.CharField(max_length=50, default=0)
category = models.CharField(choices=TYPE, default=1, max_length=25)
created_at = models.DateTimeField(auto_now_add=True)
And the model behind posting a reply in each group is:
class Reply(models.Model):
text = models.TextField(validators=[MaxLengthValidator(500)])
which_group = models.ForeignKey(Group)
writer = models.ForeignKey(User)
submitted_on = models.DateTimeField(auto_now_add=True)
image = models.ImageField(upload_to=upload_pic_to_location, null=True, blank=True )
And User is a vanilla django.contrib.auth user.
You don't have anything that is collecting the data you need. If you want to record visits to a page, you will need to build a model to do that; a simple one with FKs to User (for the visitor) and Group (for the group being visited), plus a timestamp, should be enough. Then your GroupView can make an entry in that table every time a user visits.