Defining models when using multiple databases

Question

I want to read data from an external database and generate reports in Django. I am trying to create the required models for the data that I will be fetching. Is it possible to define relationships when doing this?

For example:

I have 2 tables, ITEMS and STAKEHOLDERS, each ITEM has many STAKEHOLDERS. Is it possible to define the models such that, when I do, ITEM.objects.get(pk = 1).STAKEHOLDERS, I get all the stakeholders for that specific item?

Some additional details: I will be using custom sql to fetch the data for an ITEM and Stakeholder.

lucasnadalutti · Accepted Answer · 2016-12-08 19:20:58Z

1

You'll need a database router to direct queries on these models to the desired database.

class Item(Model):
    _database = 'legacy'

    # fields...


class Stakeholder(Model):
    _database = 'legacy'

    item = ForeignKeyField(Item, related_name='stakeholders')
    # fields...

# ...

Item.objects.get(pk=1).stakeholders

# ...

class DbRouter(object):

    def db_for_read(self, model, **hints):
        database = getattr(model, '_database', None)
        if database:
            return database
        else:
            return 'default'

    # Implement other methods if needed (e.g. db_for_write)

# settings.py
DATABASE_ROUTERS = ['myapp.mymodule.DbRouter']

edited Dec 8, 2016 at 19:20

answered Dec 8, 2016 at 18:57

lucasnadalutti

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4 Comments

Dasith Over a year ago

I know this works for the default database, but, if I have a second legacy database, would this still work?

lucasnadalutti Over a year ago

@Dasith you mean, for example, Item belonging to a database A and stakeholder belonging to a database B?

Dasith Over a year ago

No, both in same database, but I will be using custom sql to fetch the data in the model.

lucasnadalutti Over a year ago

@Dasith I think I get it. See if the updated answer is what you need.

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