I am looking for a way to have a multiple choice field populated with choices made by a user. For example, they could have the following 3 entries: Yes, No, Unsure. I want a way to be translate this to a model.
I understand this can be done with pre-defined options using a CharField, or ChoiceField, but I haven't seen anything with "dynamic" data, such as user-generated data.
I think you shouldn't use choice fields in this case, because everytime a user creates a new option, you'll have to run a new migration.
Maybe you can create a UserOption model and create a new obj everytime a user creates a new option. Then fetch all the options the user has created when he needs to choose between them.
You can't apply user choices to a DB table. However, you could store a user's choices somewhere, such as a User's Profile, and use them in a dynamically constructed form with a ChoiceField to constrain what he can put into a particular database column / model field.
Could be a PITA if he decides to delete a choice and then wants to edit the (now invalid) data in one of his records.
Related
I am using django and have three objects: Customer, Location and Department. Each has a related Setting object.
Is it better form to create a single table with optional/null foreign keys?
Or to create a different setting object/table for each of the 3 entities?
There are a few options
Create a separate Settings table and have a nullable ForeignKey from all of your objects to the Settings table. If you choose this option, you should create an abstract base class that has a ForeignKey to the Settings table and inherit from that abstract base class. That way you don't have to add the ForeignKey every time you create a new model.
Create a separate Settings table and use GenericForeignKeys from the Settings table to reference your object (Customer, Location, and Department). This has the advantage of not having an extra column in all of your tables that need settings. However, you can't do DB joins with GenericForeignKeys via the Django ORM's normal API. You'd have to use raw sql. Also, select_related doesn't work on GenericForeignKeys so you'd have to use prefetch_related instead.
Store the settings in a column in the database. You should interact with the data in some format (I like JSON) and then serialize it to a string to store in the DB. Then to read the settings, you could deserialize the string back into JSON and interact with it. With this method, you wouldn't need to join with another table to get settings, and wouldn't need to run migrations every time you added new settings. You also wouldn't need a separate Settings table. However, constructing a query to find objects with certain settings would be a pain the query would probably be slow as well.
Each option has its pros and cons; so, pick your poison ;)
So I have a list of unique pupils (pupil is the primary_key in an LDAP database, each with an associated teacher, which can be the same for several pupils.
There is a box in an edit form for each teacher's pupils, where a user can add/remove an pupil, and then the database is updated according using the below function. My current function is as follows. (teacher is the teacher associated with the edit page form, and updated_list is a list of the pupils' names what has been submitted and passed to this function)
def update_pupils(teacher, updated_list):
old_pupils = Pupil.objects.filter(teacher=teacher)
for pupils in old_pupils:
if pupil.name not in updated_list:
pupil.delete()
else:
updated_list.remove(pupil.name)
for pupil in updated_list:
if not Pupil.objects.filter(name=name):
new_pupil = pupil(name=name, teacher=teacher)
new_pupil.save()
As you can see the function basically finds what was the old pupil list for the teacher, looks at those and if an instance is not in our new updated_list, deletes it from the database. We then remove those deleted from the updated_list (or at least their names)...meaning the ones left are the newly created ones, which we then iterate over and save.
Now ideally, I would like to access the database as infrequently as possible if that makes sense. So can I do any of the following?
In the initial iteration, can I simply mark those pupils up for deletion and potentially do the deleting and saving together, at a later date? I know I can bulk delete items but can I somehow mark those which I want to delete, without having to access the database which I know can be expensive if the number of deletions is going to be high...and then delete a lot at once?
In the second iteration, is it possible to create the various instances and then save them all in one go? Again, I see in Django 1.4 that you can use bulk_create but then how do you save these? Plus, I'm actually using Django 1.3 :(...
I am kinda assuming that the above steps would actually help with the performance of the function?...But please let me know if that's not the case.
I have of course been reading this https://docs.djangoproject.com/en/1.3/ref/models/querysets/ So I have a list of unique items, each with an associated email address, which can be the same for several items.
First, in this line
if not Pupil.objects.filter(name=name):
It looks like the name variable is undefined no ?
Then here is a shortcut for your code I think:
def update_pupils(teacher, updated_list):
# Step 1 : delete
Pupil.objects.filter(teacher=teacher).exclude(name__in=updated_list).delete() # delete all the not updated objects for this teacher
# Step 2 : update
# either
for name in updated_list:
Pupil.objects.update_or_create(name=name, defaults={teacher:teacher}) # for updated objects, if an object of this name exists, update its teacher, else create a new object with the name from updated_list and the input teacher
# or (but I'm not sure this one will work)
Pupil.objects.update_or_create(name__in=updated_list, defaults={teacher:teacher})
Another solution, if your Pupil object only has those 2 attributes and isn't referenced by a foreign key in another relation, is to delete all the "Pupil" instances of this teacher, and then use a bulk_create.. It allows only 2 access to the DB, but it's ugly
EDIT: in first loop, pupil also is undefined
I need to query for a set of objects for a particular Model, change a single attribute/column ("account"), and then save the entire queryset's objects as new objects/rows. In other words, I want to duplicate the objects, with a single attribute ("account") changed on the duplicates. I'm basically creating a new account and then going through each model and copying a previous account's objects to the new account, so I'll be doing this repeatedly, with different models, probably using django shell. How should I approach this? Can it be done at the queryset level or do I need to loop through all the objects?
i.e.,
MyModel.objects.filter(account="acct_1")
# Now I need to set account = "acct_2" for the entire queryset,
# and save as new rows in the database
From the docs:
If the object’s primary key attribute is not set, or if it’s set but a
record doesn’t exist, Django executes an INSERT.
So if you set the id or pk to None it should work, but I've seen conflicting responses to this solution on SO: Duplicating model instances and their related objects in Django / Algorithm for recusrively duplicating an object
This solution should work (thanks #JoshSmeaton for the fix):
models = MyModel.objects.filter(account="acct_1")
for model in models:
model.id = None
model.account = "acct_2"
model.save()
I think in my case, I have a OneToOneField on the model that I'm testing on, so it makes sense that my test wouldn't work with this basic solution. But, I believe it should work, so long as you take care of OneToOneField's.
I'm currently implementing a solution using django admin, it allows users to define in the db a product, and then custom attributes and details, more details may be aggregated by a common attribute, this allows me to query with ajax a custom view that returns some JSON data to build automagically the form fields that I need directly in the same formset view (manipulating the DOM).
The current DB design follows this schema:
Catalog(name, description, photo)
Product(rel_catalog, name, base_price, photo, manufacturer_email)
ProductDetail(rel_product, rel_attribute, percentage_price, fixed_price)
ProductAttribute(rel_product, name, description)
As you may see I have a catalog, where there can be more products, a lot of details per product, aggregated by attributes. Then I simple show by default the Catalog, then the select with all available products for that catalog, then, choosing the right Product, I obtain the complete form (each row has a label with ProductAttribute.name and a select with related ProductDetail).
All works pretty dam good, but I also need to store this references in the DB when someone completes the form (making an order with choosen products). This forms are displayed as StackedInline (the ModelAdmin is for the Order).
I don't know how many options there may be per product so I was thinking to use this design to track orders:
Order(customer, status, notes, tot_price, inserted_by)
OrderItem(rel_order, catalog, product, unit_price)
But I don't know how to store the dynamic added inputs...
I was thiking to implement OrderItemProperty(rel_orderitem, rel_productdetail, rel_productattribute) to store each single input... but how do I loop over this unknown fields?
Maybe do you suggest a better design?
If you need more code just ask for it and I'll reply with a pastebin link.
Thankyou.
Finally I got a working solution,
I've created a custom view, overriding the default "add/" view, this way I can customize whatever I want to and I can read the POST data handling each validation, putting then the data in the right model.
I am a bit stuck on how I should model this out.
Here is what I have:
I have a model called Location. In this model I have postal code, city, region, longitude, and latitude. This data is pre-populated with all of Canada's stuff. You can imagine this table is quite large.
This is what I would like to achieve by stuck on how to model this:
I would like to create a second model called Item. Each one of these items will need to be tied to a location from the said above model. The user-story would be as follows:
User adds an item: I already know their postal code and city based on their cookie that I set.
User submits the form with their item: this is where I am confused as to how to model this data so that the item gets saved in the proper location.
I figured a FK would be the way to go but that is waaaaay to inefficient for a number of obvious reasons (huge list, and requires user input but I already know their location before saving). So, since I already know their location based on their cookie, should create a new field in the Item model called location and just save the postal code in this model? If I did this I guess I would have to query the location model for that location to pull in proper info. I am not sure what the best to go about this is, please help.
If you already know the user's location, and they're just entering an item, then the Item model should have a foreign key to Location, but you don't prompt for it on the form. Instead, fill in the Location before you save the item.
If you're using a ModelForm, then you'll want to exclude your location field so that it isn't displayed. You'll also want to set commit=False so that you can fill in the location yourself before saving the form data to the Item table.