Django Models

Use the following guidelines when working in models.py files.

Best Practices

Important Patters

• Models are where we pull and organize information about our data structures.
• Methods on the model do NOT save the data! Any logic that processes or performs actions on the database lives in the service layer.
• Methods on the model can aggregate and display information related to the model.
• Breadcrumb classes are on the model.
• Model names follow the hierarchy of the directory structure. For example, inventory_batch would have a batch module inside of the inventory module.

Example

class InventoryBatch(HistoryModelMixin, ActivityMixin):
    product = models.ForeignKey(
        'product.Product',
       
        related_name='batches',
        related_query_name='batch'
    )
    
    location = models.ForeignKey(
        'inventory_location.InventoryLocation', # note here how the patter is app_name.ModelName. 
       
        related_name='inventory',
        related_query_name='inventory',
        null=True,
        blank=True
    ) 

    name = models.CharField(max_length=255)

    unit_of_measure = models.CharField(
        max_length=3,
        choices=ProductUnitOfMeasureChoices.choices,
        default=ProductUnitOfMeasureChoices.LB
    )

Model Fields

Model Foreign Keys

• Foreign key relationships are always the first fields at the top of the model file sorted alphabetically.
• The relationship is aways a string that is of format 'app_name.ModelName'.
  • Review the related model apps.py file to find the app_label
• Do not import the related model.
• Foreign key relationships are always at the top of the model and formatted with line breaks.
• related_name It should read like English with the related model. Typically, it is the plural version but doesn't have to be.
  • readability is most important
  • eg. product.batches.all()
• related_query_name is the singular version of the word.
  • eg. Inventory.objects.filter(batch__name='Bin 4')

Example

class InventoryBatch(HistoryModelMixin, ActivityMixin):
    product = models.ForeignKey(
        'product.Product',
       
        related_name='batches',
        related_query_name='batch'
    )
    
    location = models.ForeignKey(
        'inventory_location.InventoryLocation', # note here how the patter is app_name.ModelName. 
       
        related_name='inventory',
        related_query_name='inventory',
        null=True,
        blank=True
    )

Choice Fields

• Label is all capital letters and snakecase
• The tuple is (code, verbose_name). Code is always 3 characters.

Example

# app/product/choices.py
from django.db.models import TextChoices

class ProductTypeChoices(TextChoices):    
    RAW = 'raw', 'Raw'
    WORK_IN_PROGRESS = 'wip', 'Work in Progress'
    FINISHED_GOOD = 'fin', 'Finished Good'

# app/product/models.py
from django.db import models
from app.product import choices


class Product(models.Model):

    unit_of_measure = models.CharField(
      max_length=3,
      choices=choices.ProductUnitOfMeasureChoices.choices,
      default=choices.ProductUnitOfMeasureChoices.LB
  )

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