Single Django model, multiple tables?

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Question :

Single Django model, multiple tables?

I have several temporary tables in a MySQL database that share the same schema and have dynamic names. How would I use Django to interface with those tables? Can a single model draw data from multiple tables?

Asked By: exupero


Answer #1:

You could, I believe, make a factory function that would return your model with a dynamic db_table.

def getModel(db_table):
  class MyClass(models.Model):
     # define as usual ...
     class Meta:
       db_table = db_table

  return MyClass

newClass = getModel('29345794_table')
newClass.objects.filter( ...

EDIT: Django does not create a new instance of the class’s _meta attribute each time this function is called. Creating a new instance for _meta it is dependent upon the name of the class (Django must cache it somewhere). A metaclass can be used to change the name of the class at runtime:

def getModel(db_table):
  class MyClassMetaclass(models.base.ModelBase):
    def __new__(cls, name, bases, attrs):
      name += db_table
      return models.base.ModelBase.__new__(cls, name, bases, attrs)

  class MyClass(models.Model):
    __metaclass__ = MyClassMetaclass

    class Meta:
      db_table = db_table

  return MyClass

not sure if it can be set dynamically on an already-defined class. I haven’t done this myself but it might work.

You can set this whenever.

>>> MyModel._meta.db_table = '10293847_table'
>>> MyModel.objects.all()
Answered By: Skylar Saveland

Answer #2:

Create a model for your table dynamically.

from django.db import models
from django.db.models.base import ModelBase

def create_model(db_table):

    class CustomMetaClass(ModelBase):
        def __new__(cls, name, bases, attrs):
            model = super(CustomMetaClass, cls).__new__(cls, name, bases, attrs)
            model._meta.db_table = db_table
            return model

    class CustomModel(models.Model):

        __metaclass__ = CustomMetaClass

        # define your fileds here
        srno = models.IntegerField(db_column='SRNO', primary_key=True)

    return CustomModel

and you can start querying the database.

In [6]: t = create_model('trial1')

In [7]: t._meta.db_table
Out[7]: 'trial1'

In [8]: t.objects.all()  # default db
Out[8]: [<CustomModel: CustomModel object>, '(remaining elements truncated)...']

In [9]: t.objects.using('test').all()  # test db
Out[9]: [<CustomModel: CustomModel object>, '(remaining elements truncated)...']
Answered By: ChillarAnand

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