From the knowledge I have, one has two approaches: code first or database first.
There are frameworks where one defines the models and the relationships, and auto migrate creates the database in the mirror of what one has defined.
Tried to find something reverse, but appears to me that Django does what I mentioned first - if one created the class models and migrated, then Django would create the entity database model for us.
Considering I started with the database, I don't know anything automatic to do this or the best way to tackle it.
You have two different ways to do that from the Class Diagram:
• Create the models and do the migration to create the DB.
• Create the DB and then integrate it just like you would do with a Legacy DB - as it shows in Jon Clements comment .
Related
I have a few databases in MongoDB that I want to create models for dynamically, since there are many databases and I cannot do it manually. Questions:
What should my models.py look like? (Does inspectdb work with mongodb databases or only SQL based dbs?)
Since the database models are created dynamically, how do I code the serializer class to return the dynamic fields?
Thanks in advance.
Django supports an object-relational mapper, that is aimed at traditional relational databases. While there are a number of mongodb packages for Django, none of them support inspectdb to construct your models. Either way, inspectdb is a kludge designed as a one of process to help a one-of migratation away from a legacy system, i.e. you'd build your models.py file once and never run inspectdb again. This is not what you want to do, as you seem to want dynamic models that can be added or altered at runtime.
On the bright side, Django MongoDB Engine has some support for arbitrary embedded models within pre-defined models. But even then they don't seem too supportive of it:
As you can see, generic embedded models add a lot of overhead that bloats up your data records. If you want to use them anyway, here’s how you’d do it...
In summary, try to build your models as best you can to actually match your requirements. If you know nothing about your models ahead of production, then perhaps Django isn't the right solution for you.
My django project uses django-helpdesk app.
This app has Ticket model.
My app got a Client model, which should have one to many relationship with ticket- so I could for example list all tickets concerning specific client.
Normally I would add models.ForeignKey(Client) to Ticket
But it's an external app and I don't want to modify it (future update problems etc.).
I wold have no problem with ManyToMany or OneToOne but don't know how to do it with ManyToOne (many tickets from external app to one Client from my app)
Even more hacky solution: You can do the following in the module level code after you Client class:
class Client(models.Model):
...
client = models.ForeignKey(Client, related_name='tickets')
client.contribute_to_class(Ticket, name='client')
I haven't fully tested it (I didn't do any actual database migrations), but the correct descriptors (ReverseSingleRelatedObjectDescriptor for Ticket and ForeignRelatedObjectsDescriptor for Client) get added to the class, and South recognizes the new fields. So far it seems to work just like a regular ForeignKey.
EDIT: Actually not even that hacky. This is exactly how Django sets up foreign keys across classes. It just reverses the process by adding the field when the reverse related class is built. It won't raise an error if any of the original fields on either model is shadowed. Just make sure you don't do that, as it could potentially break your code. Other than that, I don't think there should be any issues.
There are (at least) two ways to accomplish it:
More elegant solution: Use a TicketProfile class which has a one-to-one relation to Ticket, and put the Client foreign key into it.
Hacky solution: Use a many-to-many relation, and manually edit the automatically created table and make ticket_id unique.
I have a django app which consists of 17 models. Now I have realized that these models should be in 3 different apps(not in the original app). So now I would like to migrate these models out of the original app to these 3 different apps. How do I do that?
There exists foreign key, generic foreign key and ManyToMany relationships among the models. I also have data in the database(MySql), so I would like the data to be preserved during migration.
I have installed south for migrations, but don't know how to use it for solving this issue. I have gone through this similar question but could not find an answer that would solve my problem. Would be thankful for any help !
In my opinion, you have two ways of completing this task as stated below:
Move the models and add Meta.db_table to refer the existing sql table as needed as #kroolik suggested
Perform a three steps migration
The former is easier while the later could be better as tables would be named as you expect.
First of all, you mention you already has south installed. The first step would be to create the initial migration for the existing app. Take a look to the south tutorial. Then you must apply that migration, but as you already has the tables in db it would fail unless you include --fake flag.
After that you need to create the three apps you mention, and their models. Also create and apply (this time without fake flag) the initial migration for them.
Next step is write a datamigration. You must write it manually, although you can create the skeleton with datamigration. You must write "by hand" the migration.
Now you are almost done, the only remaining thing is remove the original tables. You can just remove those models, and create an "auto" schemamigration.
Don't forget to apply the migrations with migrate command. Also as #Bibhas mention a copy of database and/or a dump of it is a pretty good idea.
I have Django application with 30+ models. I want to write an application that can take a snapshot of the data in some of the models. I want to write the models once and reuse them in each application so that if I maintain it in one place, the only difference being that when I call python manage.py syncdb the same table are created with different table prefixes.
Is there any way to do this?
This is exactly where the reusable app principle comes into play.
(as explained at the django website)
I am developing a Django app being a Web frontend to some Oracle database with another local DB keeping app's data such as Guardian permissions. The problem is that it can be modified from different places that I don't have control of.
Let's say we have 3 models: User, Thesis and UserThesis.
UserThesis - a table specifying relationship between Thesis and User (User being co-author of Thesis)
Scenario:
User is removed as an author of Thesis by removing entry in UserThesis table by some other app.
User tries to modify Thesis using our Django app. And he succeeds, because Guardian and Django do not know about change in UserThesis.
I thought about some solutions:
Having some cron job look for changes in UserThesis by checking the modification date of entry. Easy to check for additions, removals would require looking on all relationships again.
Modifying Oracle DB schema to add Guardian DB tables and creating triggers on UserThesis table. I wouldn't like to do this, because of Oracle DB being shared among number of different apps.
Manually checking for relationship in views and templates (heavier load on Oracle).
Which one is the best? Any other ideas?
I decided to go with manually checking the permissions, caching it whenever I can. I ended up with get_perms_from_cache(self, user) model method which helps me a lot.