How to implement non-database backed models in Django? - django

I have an existing Django application with a pretty typical model implementation that's backed by a database. My task is to change this model so that instead of fetching the information from a database, it now fetches it from a service (e.g., via HTTP). Because there is existing code which already makes use of this model, it would be nice to maintain the same model interface so that it continues to behave like a typical Django model.
This raises a few of questions:
Is it possible to do this without having to re-write the interface from scratch to make it look like Django's model interface? (This stackoverflow question would seem to suggest otherwise: Django MVC pattern for non database driven models?)
Would writing a custom manager for this model be an appropriate approach (or have I misunderstood the role of the manager)?
Due to the service-backed nature of the new model, caching will be much more important than before. Is this something that should be implemented at the model level?

Have a look at django-roa. From the sound of it, it might be exactly what you are looking for.

Related

Django Rest Framework communicating with mobile app instances

I would like to build a REST Service which exchanges JSON messages with instances of a mobile app for registering patron traffic in physical locations of (public and academic) libraries.
I plan on using Django Rest Framework, and using Django and DRF for the first time, have some questions (rather, recommendation requests). I have read the tutorials and followed some of them, and it looks very promising indeed.
As I am quite confident with Object oriented coding in Python, I will be using class based views. Any reason not to?
The intended usage of the system will include many different libraries with their own ids, users and properties. The data model behind is thus fairly complex, and implemented with MySQL. I feel I will have better control on the data exchange, updates inserts and selects, with custom SQL queries, and would like the DRF to handle mostly authentication and the routing of messages to and from the instances of the mobile app. Is this a misconception on my part, and would it be better to let DRF handle all database-involved aspects?
Given that I follow the custom SQL approach:
As (authenticated) user IDs are interwoven with the rest of the activities (e.g. we would like to know which of the authenticated users stands behind a certain registration of activity), it would seem "simple" to use a single database for both the business model itself and the DRF-controlled aspects. Is it recommended ? Are there any aspects that need to be considered here?
I have not found similar projects to be learning from. Anybody knows a similar project?
I know it is not very concrete, but hope to elevate my understanding a bit while endeavoring on the task.
Michael
I have tried to keep this as unopinionated as possible. Mostly reffering from Django's and DRF's documentation to make sure.
Class based views have some implicit code flows, need method overrides at some places. But since you are quite comfortable with Class based views, it is far more superior in the following ways: cleaner code, much more DRY compliant than function based, easier to extend, keeps your code base more maintainable as it grows.
Django's ORM is pretty powerful and if used correctly it can provide a vareity of capabilities.
Unless your authentication system is very complex and needs to scale independently, having everything in the same DB makes sense. The chatter reduces and you will be able to utilise powerful Django and DRF's features.

Django app has multiple database and multiple user

I have written one Django cloud based app. This app will have multiple user and for them multiple database, so that their data should be separate and they can save only to same database.
1) How can we implement it
2) How to automatically one user from login page to assign the database to write on it.
I don't have a complete answer, since you do not give a lot of detail. But here are a couple ots that f hinDjango supports custom database router implementations. A database router is a class that helps django decide which database to use for a particular model. Unfortunately I don't think this mechanism is granular enough for your needs. You can also specify the database to use in your code by using using(name) queryset method and save(using=name) form of save() method for instances. Of course this also means that some features of Django are going to be unvailable to you, since you cannot always expect to have a user. Look at the docs here for more info
https://docs.djangoproject.com/en/dev/topics/db/multi-db/

Way of reusing loopback model

I have to implement reporting application that requires fetching data from existing ITS such as Jira.
I was able to login by extending StrongLoop's User model and calling REST API from JIRA.
Now, I want to share this codes by creating loopback component or something so that I could use this login method later on.
Please share your knowledge or best practice for creating loopback component.
Thanks
You probably want to look at writing a model "mixin", but without seeing your code it's hard to say exactly what that would look like. You might also just define an internal-only model that extends the built in User and then additional models that extend your new model and are actually implemented in the REST API.

Django : looking for an implementation of an ldap db backend (or for any help on this)

Following this post (I was looking for a library allowing me to declare Django models on a ldap backend), I have decided to use ldapdb. After having played a while with this library, I figured out that it doesn't reach the level of control I need, and I am therefore looking for other solutions. What I am thinking of now is implementing a Django db backend based on python-ldap.
EDIT
I need this because I am currently implementing a user/group management system on a ldap directory (it requires to be able to manipulate not only users, but different classes of ldap objects as well). So basically, I would like to be able to use (nearly) full Django orm, but with a ldap backend.
Because I love Django (and would be rather motivated in learning the dirty low-level details of db.backends), and because there's already a lot of things implemented in this project, I would like to stick to Django (unless somebody has a very good reason why I shouldn't, and a very good alternative !).
Do some of you have a simpler solution to this problem ?
Do some of you know about an implementation of such a thing (ldap db backend) ?
Do some of you know some good reads to get started on "implementing a Django db backend"?
Are some of you interested in helping with this project ?
You make a lot of bold statements such as "lots of things broken because of the way it is implemented" and "the subclassing is very very far from being complete", would you care to elaborate on them? As the author of django-ldapdb I would welcome your suggestions as to what you would like changed/fixed, that's what the django-ldapdb mailing list is for!
FYI, I took the approach of subclassing the Model class because you will usually want to have just a couple of models using the LDAP backend, not all the models in your application, and django 1.1 did not support multiple databases. Also, LDAP is very different from existing SQL backends:
is not a relational database
it is not "flat", it is a tree-like
the true "primary key" for an entry is the Distinguished Name (DN), which is not an actual field, but a value computed from other fields
fields can be multi-valued
For all these reasons, I have serious doubts as to what can be achieved by writing a true LDAP backend. I think you will always have some LDAP-specific quirks, and subclassing Model allows just that.
Your best bet is probably to write an authentication backend for the application. Here is some documentation about it:
http://docs.djangoproject.com/en/dev/topics/auth/?from=olddocs#writing-an-authentication-backend
And here is an article that explains how to extend the User model to enable you to use this authentication backend seamlessly:
http://scottbarnham.com/blog/2008/08/21/extending-the-django-user-model-with-inheritance/
Seems like there's no really good solution. And doing everything without Django's ORM is no good solution either.
I'll make new attempt at solving that problem soon, with a django-orm-based solution.

django: Selecting a freign key from 2 models

I am developing a blog styled application. I want to implement something like custom tags. (Trying to do the tag app myself, so I can learn something).
So I want to be able to create tags in admin interface, and want to be able to assign the to either my Section or Article model. I wonder if that's possible to make an model which will give ability to chose object (e.g. article or section)
I was looking on django comments app, but I would like to do something more simple. Is that possible?
Have a look at generic relations. A generic foreign key enables you to have have a foreign key relationship without having to define the target model in the code.
But I'd recommend to use django-tagging, which is a ready-made generic django tagging application which provides you a lot of additional functionality and is pretty easy to integrate (it also works via generic relations).