I am creating an electronic reference library for my school, where I have created a custom admin page (not the Django admin page). And in my requirements there needs to be a specific 'settings' page where I can store small information such as
How frequently to create reports
How frequently users should change their passwords etc.
These kinds of custom settings are not available in Django by default. But is there a way I can implement it in my app? And how should I store this information? Should I create another table to store these information?
Please let me know how to tackle such a situation.
Thanks!
Yes, the best way would probably be just to create another table for your settings.
That is because:
a. Django provides good tools for DB management, so it is less to worry about the infra.
b. You will usually have a DB access. You cannot say the same about other resources, depends on your server.
Just do something like this:
Then you may want to ensure somehow you only have one record, you can look here for example.
class MySettings(models.Model):
setting1 = models.IntegerField(default=10)
setting2 = models.IntegerField(default=11)
There are alternatives, of course, for example creating a simple dict containing your settings, and add some methods to serialize it to the local disc, in a well known location. Something like this:
import json
MY_SETTINGS_LOCATION = "/path/to/my/settings.json"
def load_settings() {
with open(MY_SETTINGS_LOCATION, "r") as f:
return json.load(f)
}
def save_settings(settings) {
with open(MY_SETTINGS_LOCATION, "w") as f:
return json.dump(settings, f)
}
Related
Consider the following scenario:
Our Django database objects must rely on IDs that are provided by external service A (ESA) - this is because we use this ID to pull the information about objects that aren't created yet from the external directly. ESA might shut down soon, so we also pull information about the same objects from external service B (ESB), and save them as a fallback.
Because these IDs are relied on heavily in views and URLs, the ideal scenario would be to use a #property:
#property
dynamic_id = ESA_id
And then, if ESA shuts down, we can switch easily by changing dynamic_id to ESB_id. The problem with this though, is that properties cannot be used in queryset filters and various other scenarios, which is also a must in this case.
My current thought is to just save ESA_id, ESB_id, and dynamic_ID as regular fields separately and assign dynamic_ID = ESA_id, and then, in case ESA shuts down, simply go over the objects and do dynamic_ID = ESB_id.
But I feel there must be a better way?
Having ESA_id and ESB_id fields in the same table is a good solution, then you have some kind of setting (DEFAULT_SERVICE_ID='ESA_id'|'ESB_id') and your code change the lookup based on this option.
Here you can see an aproach to create filters dynamicly
https://stackoverflow.com/a/310785/1448667
My django app uses update_or_create() to update a bunch of records. In some cases, updates are really few within a ton of records, and it would be nice to know what got updated within those records. Is it possible to know what got updated (i.e fields whose values got changed)? If not, does any one has ideas of workarounds to achieve that?
This will be invoked from the shell, so ideally it would be nice to be prompted for confirmation just before a value is being changed within update_or_create(), but if not that, knowing what got changed will also help.
Update (more context): Thought I'd give more context here. The data in this Django app gets updated through various means (through users coming on the web site, through the admin page, through scripts (run from the shell) that populate data from a csv etc.). The above question is important mostly for the shell scripts that update data from csvs, hence a solution at the database/trigger/signal level may not be helpful here (I guess).
This is what I ended up doing:
for row in reader:
school_obj0, created = Org.objects.get_or_create(school_id = row[0])
if (school_obj0.name != row[1]):
print (school_obj0.name, '==>', row[1])
confirmation = input('proceed? [y/n]: ')
if (confirmation == 'y'):
school_obj1, created = Org.objects.update_or_create(
school_id = row[0], defaults={"name": row[1],})
Happy to know about improvements to this approach (please see the update in the question with more context)
This will be invoked from the shell, so ideally it would be nice to be
prompted for confirmation just before a value is being changed
Unfortunately, databases don't work like that. It's the responsibility of applications to provide this functionality. And django isn't an application. You can however use django to write an application that provides this functionality.
As for finding out whether an object was updated or created, that's what the return value gives you. A tuple where the second value is a flag for update or create
I have made a django app that creates models and database tables on the fly. This is, as far as I can tell, the only viable way of doing what I need. The problem arises of how to pass a dynamically created model between pages.
I can think of a few ways of doing such but they all sound horrible. The methods I can think of are:
Use global variables within views.py. This seems like a horrible hack and likely to cause conflicts if there are multiple simultaneous users.
Pass a reference in the URL and use some eval hackery to try and refind the model. This is probably stupid as the model could potentially be garbage collected en route.
Use a place-holder app. This seems like a bad idea due to conflicts between multiple users.
Having an invisible form that posts the model when a link is clicked. Again very hacky.
Is there a good way of doing this, and if not, is one of these methods more viable than the others?
P.S. In case it helps my app receives data (as a json string) from a pre-existing database, and then caches it locally (i.e. on the webserver) creating an appropriate model and table on the fly. The idea is then to present this data and do various filtering and drill downs on it with-out placing undue strain on the main database (as each query returns a few hundred results out of a database of hundreds of millions of data points.) W.R.T. 3, the tables are named based on a hash of the query and time stamp, however a place-holder app would have a predetermined name.
Thanks,
jhoyla
EDITED TO ADD: Thanks guys, I have now solved this problem. I ended up using both answers together to give a complete answer. As I can only accept one I am going to accept the contenttypes one, sadly I don't have the reputation to give upvotes yet, however if/when I ever do I will endeavor to return and upvote appropriately.
The solution in it's totality,
from django.contrib.contenttypes.models import ContentType
view_a(request):
model = create_model(...)
request.session['model'] = ContentType.objects.get_for_model(model)
...
view_b(request):
ctmodel = request.session.get('model', None)
if not ctmodel:
return Http404
model = ctmodel.model_class()
...
My first thought would be to use content types and to pass the type/model information via the url.
You could also use Django's sessions framework, e.g.
def view_a(request):
your_model = request.session.get('your_model', None)
if type(your_model) == YourModel
your_model.name = 'something_else'
request.session['your_model'] = your_model
...
def view_b(request):
your_model = request.session.get('your_model', None)
...
You can store almost anything in the session dictionary, and managing it is also easy:
del request.session['your_model']
I have a Django app where multiple teams upload content that will be parsed. The app keeps track of certain common information in the parsed content. The issue here is that each team has content that needs to be parsed by a different parser because the content is in a different format (e.g. some teams have XML content, some have text, some have JSON, etc...). Each of the teams has provided a parser (a python module) that grabs the necessary info that is placed into corresponding Django models after parsing.
My question is: what is the best way to architect this in Django where each team can have their own parser setup correctly? It can be purely backend, no need for a user form or anything like that. My first thought was that I would create a Parser model with ForeignKey to each team like so:
class Parser(models.Model):
team = models.ForeignKey('Team')
module_path = models.CharField(max_length=..., blank=False)
and that module_path would be something like "parsers.teamA.XMLparser" which would reside in my app code in that path like so:
parsers/
teamA/
__init__.py
XMLparser.py
teamB/
Then when my app is coming to parse the uploaded content, I would have this:
team = Team.objects.get(id=team_id)
parser = Parser.objects.get(team=team)
theParser = __import__(parser.module_path)
theParser.parse(theStuffToBeParsed)
What problems does anyone see with this? The only other option that I can think of is to create separate Django apps for each parser, but how would I reference which team uses which app in the database (same as done here?)?
The approach you're taking seems valid to me. Keep in mind that you are effectively running arbitrary python code so I would never be using something like this on a public facing site and ensure you trust the teams writing their parsers.
You might make this a bit nicer by writing a custom Field to represent the module path that will remove the need to handle the import everytime and will instead handle the import for you and return the parse method (or maybe even better a Parser object where you could tell the teams to implement an interface)
The best example might be to look at the source for django's ImageField or even CharField. Instead of having having your model have a CharField, you'd have a "ModuleField": parser = ModuleField(). The database stored value would indeed be the path to the module (so simply make it a subclass of CharField), but override the to_python method. In your new to_python method handle importing the module and return a python object.
That python object could be anything you want it to be, from your example you could return theParser.parse. This would result in if you have a Parser instance foo you could the_parser_method = foo.parser
I am new to Django, and probably using it in a way thats not normal.
That said, I would like to find a way to have site wide memory.
To Explain.
I have a very simple setup where one compter will make posts to the site every few seconds.
I want this data to be saved off somewhere.
I want everyone who is viewing the webpage to see updates based on this data in near real time via some javascript.
So using the sample code below.
Computer A would do a post to set_data and set data to "data set"
Computer B,C,D,etc.... would then do a get to get_data and see "data set"
Unfortunatly B,C,D just see ""
I have a feeling what i need is memcached, but I am on a hostgator shared server and cannot install that. In the meantime I am just writing them to files. This works but is really inneficient, and I am hopeing to serve a large user base.
Thanks for any help.
#view.py
data=""
def set_data(request):
data = request.POST['data']
return HttpResponse("");
def get_data(request):
return HttpResponse(data);
memcached is lossy, hence doesn't fulfil "persistent".
Files are fine, but switch to accessing them via mmap.
Persistent storage is also called database (although for some cases Django's cache backend might work as well). Don't ever try to use global variables in web development.
Whether you should use a Django model or the cache backend really depends on your use case, but you just described a contrived example (or does your web app consist of a getter and a setter?).