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In Django Tables2, how do you make a column show text from a table referenced by a foreign key?

After reading all the docs and answers I can find, and burning a whole day, I still can't make this work. Using Django Tables2, I want to show a list of instruments; the instruments table includes a foreign key to an instrumentsType table. When I list the instruments and their attributes, I want to use the foreign key to substitute the textual instrument type description from the other table. I have tried every combination of double underscores and other accessor techniques, but so far all I get is the dreaded -- in the column. (Displaying just the record ID works).
from .models import Instrument
from django_tables2 import A
from instrumenttypes.models import InstrumentType
class InstrumentTable(tables.Table):
id = tables.LinkColumn('instrument_details', args=[A('station_id')])
class Meta:
model = Instrument
template_name = "django_tables2/bootstrap.html"
fields = ("id", "instrument", "nickname", "serialNo",
"instrument__instrumenttype_id__instrumenttypes__id_instrumentType" )
The models involved are:
Instruments model.py
from django.db import models
from instrumenttypes.models import InstrumentType
from stations.models import Station
# Create your models here.
class Instrument(models.Model):
instrument = models.CharField(max_length=40)
instrumenttype = models.ForeignKey(InstrumentType, on_delete=models.CASCADE, null=True)
station = models.ForeignKey(Station, on_delete=models.CASCADE, default=1)
serialNo = models.CharField(max_length=60, null=True, blank=True)
dateAdded = models.DateTimeField("Date Added", null=True, blank=True)
dateRemoved = models.DateTimeField("Date Removed", null=True, blank=True)
status = models.CharField(max_length=10, null=True, blank=True)
nickname = models.CharField(max_length=40, null=True, blank=True)
InstrumentTypes model.py
from django.db import models
class InstrumentType(models.Model):
instrumentType = models.CharField(max_length=40)
Resulting output:
ID Instrument Nickname SerialNo Instrumenttype
4 instr2 nock2 123 —
The most relevant online references I have found are here and here; but having tried the suggestions, no luck. What am I missing?

I've been struggling to get something working too (but I finally did), and I found the examples too brief.
I think you want to get rid of this stuff in the Meta class
"instrument__instrumenttype_id__instrumenttypes__id_instrumentType"
I think Meta.fields should just be a list of field names, and that you refer to the attribute in the other table from the point of view of the type of object you will later pass in to the IntrumentTable constructor (and that is named in the Meta.model attribute:
from django_tables2.utils import Accessor
class InstrumentTable(tables.Table):
instrument_type = tables.Column(accessor=Accessor('instrumenttype.name'))
class Meta:
model = Instrument
template_name = "django_tables2/bootstrap.html"
fields = ("id", "instrument", "nickname", "serialNo", "insrument_type")
Then, in view, make an instance of InstrumentTable
def myview(request):
table_to_render = InstrumentTable(Instrument.objects)
return render(request, sometemplate, {table: table_to_render})
You didn't show your view, and I know there may be a different way. If you have the whole thing in a repo somewhere, leave a link.

Django - ask user for menuitem choices on each menu item

I am developing a simple restaurant app in django and mysql and after days of googling and research, i wasn't able to find a suitable answere for this particular problem, here is my django Model
class MenuItem(models.Model):
menu_category = models.ForeignKey(MenuCategory, to_field='slug', on_delete=models.CASCADE)
name = models.CharField(max_length=30)
image = models.ImageField(upload_to='uploads/menu/')
slug = models.SlugField(null=True, blank=True, unique=True)
price = models.DecimalField(max_digits=9, decimal_places=0)
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
def __str__(self):
return self.name
and here is the problem:
for example i have a menuItem "MEXICAN BURGER" i would like to ask the user their choice of meat.. ie either chicken or beef, or their choice of bread, white or brown,
or i might be having a MenuItem "OMELETTE COMBO" and i would like to ask the user the type of omellete they'd like to have eg ('spanish omelete', 'spinach and mushroom omelete')
or i might be having a MenuItem "ESPRESSO" and i would like them to choose between ('single', 'double')
*one menuitem can have multitple choices related to it, ie burger item can have choice of bread as well as choice of meat
for a better understanding of my problem visit this
link
*
and this another link

You can create another model as needed e.g. MeatOption and add to it a ForeignKey to MenuItem:
class MeatOption(models.Model):
meat_type = models.CharField(max_length=200)
class MenuItem(models.Model):
meat_type = models.ForeignKey(MeatOption, null=True, blank=True)
# rest of fields
Ideally you should think of categorizing your items and reflect that categorization into your models. i.e. you could have class Burgers, class Beverages and so on, so that you only include the relevant options.
And if there is common functionality among all those categories you could inherit that from a Base MenuItem class like so:
class MenuItem(models.Model):
# common fields across all items go here
class Burger(MenuItem):
# burger-specific fields here
meat_type = models.ForeignKey(MeatOption)
class Omelette(MenuItem):
# omelette-specific fields here
ingredient = models.ManyToManyField(Ingredient)
class Ingredient(models.Model):
name = models.CharField(max_length=200)
the details depend on your use-case of course

There are different solutions to this.
Code Based: Inheritance
You create Mixins for each of your choice type and subclass MenuItem and these mixins.
from django.db.models import CharField, TextChoices, Model
class MeatChoices(TextChoices):
CHICKEN = 'chi'
BEEF = 'bee'
class MeatMixin(Model):
meat_choices = CharField(max_length=3, choices=MeatChoices.choices, default=MeatChoices.CHICKEN)
class MeatMenuItem(MeatMixin, MenuItem):
pass
This will require code changes whenever more choices are added to the menu or the menu is changed in that matter.
Data Based: Generic Models
To allow the admin user to create and add choices to the menu items via the Django Admin, you need to create a model structure that enables specifying choices:
from django.contrib.postgres.fields import ArrayField
from django.db.models import ManyToManyField, CharField, Model
class Ingredient(Model):
name = CharField(max_length=50, unique=True)
class IngredientChoiceGroup(Model):
name = CharField(max_length=50, unique=True)
# simple solution for postgres only:
# ingredients = ArrayField(CharField(max_length=50))
# if not postgres or you need more attributes to ingredient:
ingredients = ManyToManyField(Ingredient)
class MenuItem(models.Model):
menu_category = models.ForeignKey(MenuCategory, to_field='slug', on_delete=models.CASCADE)
name = models.CharField(max_length=30)
image = models.ImageField(upload_to='uploads/menu/')
slug = models.SlugField(null=True, blank=True, unique=True)
price = models.DecimalField(max_digits=9, decimal_places=0)
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
ingredient_choices = ManyToManyField(IngredientChoiceGroup)
def __str__(self):
return self.name
This method would allow to configure multiple choice groups per menu item, e.g. "BREAD" and "MEAT". And you can do that all via the Django Admin.
You might need to work out the details. This is just a draft.
Note about ArrayField: it is a simpler structure in the DB, but for the Admin you will need to add a specific widget via 3rd party library or at least write your own parser. In the end, M2M field might be the better choice.

Django when is concrete inheritance appropriate

Let me start by stating that I have looked at django-polymorphic for this and still have questions. I have item models and many subtypes for items. Currently, my models look like this.
class Item(models.Model):
pass
class Television(Item):
upc = models.CharField(max_length=12, null=True)
title = models.CharField(max_length=255, null=True)
brand = models.ForeignKey(Brand)
screen_size = models.IntegerField()
class Fridge(Item):
upc = models.CharField(max_length=12, null=True)
title = models.CharField(max_length=255, null=True)
brand = models.ForeignKey(Brand)
stuff_about_fridge = models.CharField(max_length=255, null=True)
I did this at first because then I wouldn't worry about all of the left joins when querying different item types that would be caused if my models looked like this:
class Item(models.Model):
upc = models.CharField(max_length=12, null=True)
title = models.CharField(max_length=255, null=True)
brand = models.ForeignKey(Brand)
class Television(Item):
screen_size = models.IntegerField()
class Fridge(Item):
stuff_about_fridge = models.CharField(max_length=255, null=True)
I am now reaching a point where I realize that I very often query all of the Item models together and have to left join information from the subtypes instead, so I am not really saving myself there. My question is, even if I used something like django-polymorphic, would it make sense to A) put everything that is shared in the parent model and just specific things in the child models or to B) have it like I do where everything is in the child model, but they share a parent model PK just so that they can be queried together?

"Abstract base classes are useful when you want to put some common information into a number of other models. This model will then not be used to create any database table. Instead, when it is used as a base class for other models, its fields will be added to those of the child class"
Reference: https://docs.djangoproject.com/en/3.0/topics/db/models/#abstract-base-classes
The point of using inheritance is for sharing common info as mentioned in option (A).
Django-polymorphic makes using inherited models easier, nothing more.
Reference: https://django-polymorphic.readthedocs.io/en/stable/
That means, in conclusion, option (A) is correct even though if you use Django-polymorphic.
Below method is the right approach:
class Item(models.Model):
upc = models.CharField(max_length=12, null=True)
title = models.CharField(max_length=255, null=True)
brand = models.ForeignKey(Brand)
class Television(Item):
screen_size = models.IntegerField()
class Fridge(Item):
stuff_about_fridge = models.CharField(max_length=255, null=True)

Using Model.objects.all() as a blueprint for a secondary table entry

I am having a bit of trouble with the logic of how this should work so I am hoping it is possible.
I figured out 1 possible solution that is written as an answer below, I will accept it in a few days, but if someone comes up with a better solution, I will negate any answer I post.
Overall I am working on an Apartment Move-Out/Move-In Inspection Application in Django, and in both portions I have universal Locations that must be inspected for each report. I have allowed the InspectionLocations objects to be updated/submitted by clients, which is presenting an issue in how submitted reports should be stored in my Database.
What I want is to use the InspectionLocations table as a blueprint to build an Inspection Report for Move-Ins where the form-fields are generated based on the InspectionLocations objects' location, status, and information attributes/fields.
My issue is right at this point, how do I reference those values as a blueprint to build a report submission when the number of fields in the InspectionLocations can change?
from django.db import models
from apps.units.models import Unit
class Inspections(models.Model):
class Meta:
abstract = True
id = models.AutoField(primary_key=True)
inspection_date = models.DateField()
submitted_by = models.ForeignKey(
'users.CustomUser',
default=None,
null=True,
on_delete=models.SET_NULL,
db_column='submitted_by')
last_update = models.DateTimeField(auto_now=True)
date_added = models.DateTimeField(auto_now_add=True, editable=False)
class MoveInInspections(Inspections):
unit = models.ForeignKey(Unit, on_delete=models.CASCADE, db_column='unit_id')
# should have reference to all InspectionLocation items as reference for submission, how?
class MoveOutInspections(Inspections):
unit = models.ForeignKey(Unit, on_delete=models.CASCADE, db_column='unit_id')
date_notice_given = models.DateField(blank=True, null=True, default=None)
date_vacated = models.DateField(blank=True, null=True, default=None)
# should have reference to all InspectionLocation items as reference for submission, how?
class InspectionLocations(models.Model):
'''
Defualt Inspection Locations are created when a
client is created using code like this:
InspectionLocation.objects.get_or_create(location='Living Room')
InspectionLocation.objects.get_or_create(location='Dining Room')
InspectionLocation.objects.get_or_create(location='Kitchen')
InspectionLocation.objects.get_or_create(location='Bedroom')
InspectionLocation.objects.get_or_create(location='Bathroom')
InspectionLocation.objects.get_or_create(location='Other')
'''
id = models.AutoField(primary_key=True)
location = models.CharField(max_length=50)
status = models.BooleanField(default=None)
information = models.TextField(default=None, blank=True)
I have tried ManyToMany fields and FKs but I cannot seem to get the logic working as anytime an object references an InspectionLocations object it is universally changing data for every report, which is leading be to the idea that I somehow need to use it as a blueprint.

I didn't post this in my question because it was getting long, but my best option so far seems to be to use a Django JSONField (as I am using Postgres), like so:
from django.contrib.postgres.fields import JSONField
class MoveInInspections(Inspections):
unit = models.ForeignKey(Unit, on_delete=models.CASCADE, db_column='unit_id')
data = JSONField()
class MoveOutInspections(Inspections):
unit = models.ForeignKey(Unit, on_delete=models.CASCADE, db_column='unit_id')
date_notice_given = models.DateField(blank=True, null=True, default=None)
date_vacated = models.DateField(blank=True, null=True, default=None)
data = JSONField()
To where I store the values of the InspectionLocations object's in a Dictionary

How to filter a one-to-one generic relation with Django?

I have a moderation model :
class ItemModeration(models.Model):
class Meta:
indexes = [
models.Index(fields=['object_id', 'content_type']),
]
unique_together = ('content_type', 'object_id')
content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
object_id = models.PositiveIntegerField()
item = GenericForeignKey('content_type', 'object_id')
published = models.BooleanField(default=False)
...
A descriptor to attach a moderation object on-the-fly :
class ItemModerationDescriptor(object):
def __init__(self, **default_kwargs):
self.default_kwargs = default_kwargs
def __get__(self, instance, owner):
ctype = ContentType.objects.get_for_model(instance.__class__)
try:
moderation = ItemModeration.objects.get(content_type__pk=ctype.id,
object_id=instance.pk)
except ItemModeration.DoesNotExist:
moderation = ItemModeration(item=instance,**self.default_kwargs)
moderation.save()
return moderation
And a model I want to moderate :
class Product(models.Model):
user = models.ForeignKey(
User,
null=True,
on_delete=models.SET_NULL)
created = models.DateTimeField(
auto_now_add=True,
blank=True, null=True,
)
modified = models.DateTimeField(
auto_now=True,
blank=True, null=True,
)
name = models.CharField(
max_length=PRODUCT_NAME_MAX_LENGTH,
blank=True, null=True,
)
moderation = ItemModerationDescriptor()
Now I can see a product 'published' state easily :
p=Product(name='my super product')
p.save()
print(p.moderation.published)
-> False
The generic relation is useful because I will be able to search the objects to moderate whatever the type is : it could be products, images, comments.
to_moderate_qs = ItemModeration.objects.filter(published=False)
Now, how can I get a filtered list of published products ?
I would like to do something like this
published_products_qs = Product.objects.filter(moderation__published=True, name__icontains='sony')
But, of course, it won't work as moderation attribute is not a Django model field.
How can I do that efficiently ? I am thinking a about an appropriate JOIN, but I cannot see how to do that with django without using raw SQL.

Django has a great built in answer for this: the GenericRelation. Instead of your descriptor, just define a generic relation on your Product model and use it as a normal related field:
from django.contrib.contenttypes.fields import GenericRelation
class Product(models.Model):
...
moderation = GenericRelation(ItemModeration)
Then handle creation as you normally would with a related model, and filtering should work exactly as you stipulated. To work as your current system, you'd have to put in a hook or save method to create the related ItemModeration object when creating a new Product, but that's no different from other related django models. If you really want to keep the descriptor class, you can obviously make use of a secondary model field for the GenericRelation.
You can also add related_query_name to allow filtering the ItemModeration objects based only on the Product content type.
WARNING if you do use a GenericRelation note that it has a fixed cascading delete behavior. So if you don't want ItemModeration object to be deleted when you delete the Product, be careful to add a pre_delete hook or equivalent!
Update
I unintentionally ignored the OneToOne aspect of the question because the GenericForeignKey is a one-to-many relation, but similar functionality can be effected via smart use of QuerySets. It's true, you don't have access to product.moderation as a single object. But, for example, the following query iterates over a filtered list of products and extracts their name, the user's username, and the published date of the related ModerationItem:
Product.objects.filter(...).values_list(
'name', 'user__username', 'moderation__published'
)

You'll have to use the content_type to query the table by specific model type.
like this:
product_type = ContentType.objects.get_for_model(Product)
unpublished_products = ItemModeration.objects.filter(content_type__pk=product_type.id, published=False)
For more details on the topic check contenttypes doc