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Multi-table inheritance (MTI)¶
This document describes the lino_book.projets.mti
demo project,
an application used for testing and explaining Multi-table inheritance.
The example database¶
Here is the models.py
file used for this example. This is
classical Django know-how: Restaurant inherits from Place, and
Place is not abstract. That's what Django calls multi table
inheritance.
# Copyright 2010-2020 Rumma & Ko Ltd
# License: GNU Affero General Public License v3 (see file COPYING for details)
from lino.api import dd
from django.db import models
from lino.mixins.polymorphic import Polymorphic
class Person(models.Model):
name = models.CharField(max_length=50)
def __str__(self):
return self.name
class Place(Polymorphic):
name = models.CharField(max_length=50)
owners = models.ManyToManyField(Person)
def __str__(self):
if self.pk is None:
return self.name
return "%s (owners=%s)" % (self.name, ', '.join(
[str(o) for o in self.owners.all()]))
class Restaurant(Place):
serves_hot_dogs = models.BooleanField(default=False)
cooks = models.ManyToManyField(Person)
def __str__(self):
if self.pk is None:
return self.name
return "%s (owners=%s, cooks=%s)" % (self.name, ', '.join([
str(o) for o in self.owners.all()
]), ', '.join([str(o) for o in self.cooks.all()]))
class Visit(models.Model):
allow_cascaded_delete = ['place']
person = dd.ForeignKey(Person)
place = dd.ForeignKey(Place)
purpose = models.CharField(max_length=50)
def __str__(self):
return "%s visit by %s at %s" % (self.purpose, self.person,
self.place.name)
class Meal(models.Model):
allow_cascaded_delete = ['restaurant']
person = dd.ForeignKey(Person)
restaurant = dd.ForeignKey(Restaurant)
what = models.CharField(max_length=50)
def __str__(self):
return "%s eats %s at %s" % (self.person, self.what,
self.restaurant.name)
from .ui import *
>>> rt.show("app.Persons")
========
name
--------
Anne
Bert
Claude
Dirk
Ernie
Fred
========
>>> rt.show("app.Places")
==== ===================== ================
ID name owners
---- --------------------- ----------------
1 Bert's pub *Anne*, *Bert*
2 The Chopping Shack *Anne*
3 The Abacus Well *Claude*
4 The Olive Lounge *Ernie*
5 The Autumn Bite *Anne*
6 The Private Mission *Claude*
7 Nova *Ernie*
8 Babylon *Anne*
9 Blossoms *Claude*
10 Whisperwind *Ernie*
11 Catch *Anne*
==== ===================== ================
>>> rt.show("app.Restaurants")
==== ===================== ================= ========== ========
ID name serves hot dogs owners cooks
---- --------------------- ----------------- ---------- --------
2 The Chopping Shack No *Anne* *Bert*
3 The Abacus Well No *Claude* *Dirk*
4 The Olive Lounge No *Ernie* *Fred*
5 The Autumn Bite No *Anne* *Bert*
6 The Private Mission No *Claude* *Dirk*
7 Nova No *Ernie* *Fred*
8 Babylon No *Anne* *Bert*
9 Blossoms No *Claude* *Dirk*
10 Whisperwind No *Ernie* *Fred*
11 Catch No *Anne* *Bert*
==== ===================== ================= ========== ========