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How to access (previous or next) element and compare values in django template

I was working with a django app that built under a machine learning model and its pulling data from a joblib dump file.
Everything was fine but I am getting error while accessing previous element in the template for loop.
My views.py written as-
Is there any way to access previous index and compare values for this particular problem?
Please let me know.
Thanks in advance :)

You can't access indexes like python lists on Django Template Language. You can access the specified indexes such as data.0 or data.1. For more complex cases, you need to write a custom template filter.
https://docs.djangoproject.com/en/3.2/howto/custom-template-tags/

Mongoengine change document structure

I'm trying for the first time to use mongo, and I choose mongoengine.
After defining the Document structure if I try to change it (adding a field, removing a field, renaming ecc..) the reading operations still works, but any other operation on previously stored document fail since they're note compliant anymore with the document structure.
Is there any way to manage this situation? should I only user Dynamic documents with Dictionaries instead of EmbeddedDocuments?

Using DynamicDocument or setting meta = {'strict': False} on your Document may help in some cases but the only proper solution to this is running a migration script.
I'd recommend doing this using pymongo but you could also do that from the mongo shell. Every time your model change in a way that is not compatible, you should run a migration on the existing data so that it fits the new model. Otherwise mongoengine will complain at some point (mongoengine contributor here)

Django: How to save a record in a new table before saving (user udates) the original

Scenario:
Developing a question answer app.
Here are different users can answer the questions.
Each question may have several fields to response (2 or 3 yes/No checkboxes) and any user can update any of those any time.
Problem:
I need to keep a log (with time and user name) in a different log table every time the records got any changes.
The log table is just a look alike of the original model (e.g. ChangeLogModel) just with 2 extra fields as logDate and ChangingUser.
This will help me to check the log and find the status of the question in any specific date.
Possible Solutions:
Using signals (...Not used to with signals, lack of detailed tutorials, documentation is not detailed too)
making the backup before doing any ".save()" (... Have o idea how to do that)
Install any external app (...Trying to avoid installing any app)
Summary:
Basically What I am asking for is a log table where the 'state' of the original record/row/tuple would be saved to another table (i.e. logTable) prior to hit the "form.save()" trigger.
So, every time the record got updated so the LogTable will get a new row with a datestamp.

You could use an django package for audit and history, any of those in this overview for example.
I had success using django-simple-history.

I think that the best way is just to do it straight forward. You can save the user's answer and right after that the log, wrap it with database transaction and rollback if something goes wrong.
Btw if the logs table has the same fields like the original model you might consider using foreign key or inheritance, depends on your program logic.

Dynamic database tables in django

I am working on a project which requires me to create a table of every user who registers on the website using the username of that user. The columns in the table are same for every user.
While researching I found this Django dynamic model fields. I am not sure how to use django-mutant to accomplish this. Also, is there any way I could do this without using any external apps?
PS : The backend that I am using is Mysql

An interesting question, which might be of wider interest.
Creating one table per user is a maintenance nightmare. You should instead define a single table to hold all users' data, and then use the database's capabilities to retrieve only those rows pertaining to the user of interest (after checking permissions if necessary, since it is not a good idea to give any user unrestricted access to another user's data without specific permissions having been set).
Adopting your proposed solution requires that you construct SQL statements containing the relevant user's table name. Successive queries to the database will mostly be different, and this will slow the work down because every SQL statement has to be “prepared” (the syntax has to be checked, the names of table and columns has to be verified, the requesting user's permission to access the named resources has to be authorized, and so on).
By using a single table (model) the same queries can be used repeatedly, with parameters used to vary specific data values (in this case the name of the user whose data is being sought). Your database work will move along faster, you will only need a single model to describe all users' data, and database management will not be a nightmare.
A further advantage is that Django (which you appear to be using) has an extensive user-based permission model, and can easily be used to authenticate user login (once you know how). These advantages are so compelling I hope you will recant from your heresy and decide you can get away with a single table (and, if you planning to use standard Django logins, a relationship with the User model that comes as a central part of any Django project).
Please feel free to ask more questions as you proceed. It seems you are new to database work, and so I have tried to present an appropriate level of detail. There are many pitfalls such as this if you cannot access knowledgable advice. People on SO will help you.

This page shows how to create a model and install table to database on the fly. So, you could use type('table_with_username', (models.Model,), attrs) to create a model and use django.core.management to install it to the database.

Saving datas from one database to another

I want to copy the datas from one database to another in Postgres. I wrote a script in django and was able to grab a datas from one specific table but how can i add that data in other database.New database has same table and column name, i want to save that old database files to new database.
This might be easy for some of you guys but i really couldnt figure that out.

I'm not familiar with either API but if the rows/columns have the same dimmensions you could do something like (and this is partially pseudocode):
for x in range(height):
for y in range(width):
data = call_data_from_database_A(x, y)
new_entry = enter_data_into_database_B(x, y)
Where the Call_data is you're getting data from that specific row/column, and enter_data enters the data into that specific row/column. I'm not familiar with either API but if you find the two I'm sure you could figure it out rather quickly.

Instead of writing your own import and export code, why not use the native capabilities of Postgres and dump the table from your old database then import it into your new one:
http://www.postgresql.org/docs/current/static/sql-copy.html

The simplest way to do this with Django (move one Django database to another, defined with a different model django database) is to write a 2 Django views and one jquery html page.
The first view will be in the original Django app. It will essentially create a json object model of the database and push it out on a get request. This is custom to your Django's models.
The second view will be in the new Django app. This will take in json data and format it to match your current Django database (fields might not match up exactly, hence the reason for doing this migration). You then just add elements into the new database just as you were creating a new Django model entry(example).
I personally use a one off jquery html page that gets the json data from the first view and posts it to the second one. You could exclude this piece and just write it all in python in the second view, but I find doing it this way to be much cleaner.