Create database models

Create models for storing data in the database.

In this section

• Create the Django models for storing data in the database

We're going to create a Work model and an Expression model. Both models are uniquely identified by their respective FRBR URIs.

See Introductory concepts for background on Works, Expressions and FRBR URIs.

We'll store all the raw metadata in a single metadata JSON field. We'll also extract certain fields from that metadata and store that information separately, so we can query it more easily.

models.py

from django.db import models


class Work(models.Model):
    frbr_uri = models.CharField(max_length=512, unique=True)
    title = models.CharField(max_length=512)
    metadata = models.JSONField()
        
    class Meta:
        ordering = ['title']

    def __str__(self):
        return f'{self.title} ({self.frbr_uri})'


class Expression(models.Model):
    # the expression inherits most of its metadata from its work
    work = models.ForeignKey(Work, related_name='expressions', on_delete=models.PROTECT)
    # the expression's FRBR URI is more specific than its work's
    frbr_uri = models.CharField(max_length=512, unique=True)
    # the expression's title may differ from its work's
    title = models.CharField(max_length=512)
    # the expression has a language, date, and content, which its work doesn't have
    language_code = models.CharField(max_length=3)
    date = models.DateField()
    content = models.TextField(null=True, blank=True)
    toc_json = models.JSONField()

    class Meta:
        # latest first
        ordering = ['-date']

    def __str__(self):
        return f'{self.title} ({self.frbr_uri})'

Note:

• The frbr_uri on both Work and Expression must be unique.

• One work can have multiple expressions, hence the ForeignKey from Expression to Work.

• Expressions require a work, so PROTECT any expressions if a work is deleted.

• Only key pieces of metadata needed for the legislation reader app have been specified on the Work model. The metadata field is used for storing the rest.

You'll need to make and run migrations after adding these models.

python manage.py makemigrations
python manage.py migrate