How do I batch update a field with a function in Django and The function argument is the field value . such as
Data.objects.filter(need_add=1).update(need_add=Myfunc(F('need_add')))
You can't. .update does its work at the SQL query level, i.e. inside the Database engine. Unless you can encode your function in SQL, you have to fetch the objects, update them, and save them. There is .bulk_update (link) as an optimization compared to a simple iteration over a queryset saving objects one-by-one.
Database functions here
Related
When I querying a Model in Django, I want to create a custom field (using "extra" function) which may use as a sorting field. For example,
result = foo_model.objects.filter(active=True).extra(select={'cal_field': pythonFunction()}).extra(order_by=['cal_field'])
I have 2 questions:
Can I create a field which calling a Python function inside "extra"?
If it can, how can I pass the current row into the function?
Thanks a lot!
I have several fields that contain exactly the same sql query! Is it possible to place the sql question centrally in APEX in the same way as list of values or as a function in oracle? I am using APEX 18.2
Here are two extended solutions
Pipelined SQL
https://smart4solutions.nl/blog/on-apex-lovs-and-how-to-define-their-queries/
Dynamic SQL
http://stevenfeuersteinonplsql.blogspot.com/2017/01/learn-to-hate-repetition-lesson-from.html
Call me dense, but I don't think I understand why you'd have multiple fields (presumably on the same form) whose source is the same SQL query.
Are you passing a parameter to the SQL to get a different value for each field?
If you are passing a parameter to the SQL query, why not create a database view to hold the query, then pass the parameter to the view. That way, if you need to change it, it's in one place.
If they really are all the same value from the same query, how about using the SQL for one field/page_item, then make the source for the others be the first page item?
I would create a hidden item with the query in the source as text and use &HIDDEN_ITEM_NAME. to reference its value in the source of any item I was trying to display the query.
Finally isolved it with a function and use the type PL/SQL Function Body returning SQL Query in APEX, then i have all in one place. I created a function in SQL developer that returns a SQL query.
I have a model called "Story" that has two integer fields called "views" and "votes". When I retrieve all the Story objects I would like to annotate the returned QuerySet with a "ranking" field that is simply "views"/"votes". Then I would like to sort the QuerySet by "ranking". Something along the lines of...
Story.objects.annotate( ranking=CalcRanking('views','votes') ).sort_by(ranking)
How can I do this in Django? Or should it be done after the QuerySet is retrieved in Python (like creating a list that contains the ranking for each object in the QuerySet)?
Thanks!
PS: In my actual program, the ranking calculation isn't as simple as above and depends on other filters to the initial QuerySet, so I can't store it as another field in the Story model.
In Django, the things you can pass to annotate (and aggregate) must be subclasses of django.db.models.aggregates.Aggregate. You can't just pass arbitrary Python objects to it, since the aggregation/annotation actually happens inside the database (that's the whole point of aggregate and annotate). Note that writing custom aggregations is not supported in Django (there is no documentation for it). All information available on it is this minimal source code: https://code.djangoproject.com/browser/django/trunk/django/db/models/aggregates.py
This means you either have to store the calculations in the database somehow, figure out how the aggregation API works or use raw sql (raw method on the Manager) to do what you do.
everybody.
I work with Django 1.3 and Postgres 9.0. I have very complex sql query which extends simple model table lookup with some extra fields. And it wrapped in table function since it is parameterized.
A month before I managed to make it work with the help of raw query but RawQuerySet lacks a lot of features which I really need (filters, count() and clone() methods, chainability).
The idea looks simple. QuerySet lets me to perform this query:
SELECT "table"."field1", ... ,"table"."fieldN" FROM "table"
whereas I need to do this:
SELECT "table"."field1", ... ,"table"."fieldN" FROM proxy(param1, param2)
So the question is: How can I do this? I've already started to create custom manager but can't substitute model.db_table with custom string (because it's being quoted and database stops to recognize the function call).
If there's no way to substitute table with function I would like to know if I can create QuerySet from RawQuerySet (Not the cleanest solution but simple RawQuerySet brings so much pain in... one body part).
If your requirement is that you want to use Raw SQL for efficiency purposes and still have access to model methods, what you really need is a library to map what fields of the SQL are the columns of what models.
And that library is, Unjoinify
My initial question was here and was related to the postgres backend. Postgres subquery, ordering by subquery
Now my problem has moved onwards to the Django ORM layer. I essentially want to order a query by a postgres function ('idx', taken from the above stackoverflow work)
I've gone through trying to use model.objects.extra(order_by ) or simply order_by but I believe both of these need the order_by parameter to be an attribute or a field known to Django.
I'm trying to think how to solve this without having to revert to using an entirely raw SQL query through a model manager.
You can use extra to add the function result to your query and then order by it. Something like:
MyModel.objects.extra(select={'idx': 'idx(foo, bar)'}, order_by=['idx'])