ViewedModels

Viewed Models is a simple way to add PostGres “views” which look to Django just like Models. This lets us go outside the Django ORM to create views or materialized views to harness the power of PostGreSQL without losing the power to access that data using the ORM. It is very probably compatible with other DBMS but tested only with PG.

Installation

For production:

pip install django-viewedmodels

For development:

pip install -e git+https://github.com/joshbrooks/django_viewedmodels#egg=viewedmodels

Usage

• A model which uses this framework should inherit from ViewedModel

• The model requires an “sql” method which returns the sql required to create view

• The model also requires a “dependencies” attribute. These are useful in generating table names within the SQL statement as well as dependency resolution.

• The model also requires fields specified in the standard Django way. Foreign keys should work fine.

• Foreign Keys: For ForeignKey(myApp.MyModel') we need to have a field mymodel_id returned from the SQL.

• Every Django model (including these ViewedModels) requires an ‘id’ field. We can fake this by including row_number() OVER () AS id somewhere (usually as the first item) in our SELECT statement.

Example

from django.db import models
from django.contrib.postgres.fields import JSONField
from viewedmodels.models import ViewedModel
from viewedmodels.helpers import dependency_lookup


class ActivityCommitment(ViewedModel):
    # Declaring dependencies for table lookup in the query and orderly build/ teardown of the views structure if
    # there is inheritance between ViewedModel instances
    dependencies = (
        ('aims', 'Activity'),
        ('aims', 'AidTypeCategory'),
        ('iati', 'Transaction'),
        ('aims', 'AidType'),
        ('aims', 'TransactionValueUSD')
    )

    @classmethod
    def sql(cls):
        tables = dependency_lookup(
            cls.dependencies)  # This returns a lookup for 'app_model' string to the true table name
        return '''
        SELECT
            -- Columns { id, activity_id, aidtypecategory_id, dollars } reflect our field definition for the model
            ROW_NUMBER() OVER () id, --Note how an id field is autogenerated for Django's sake
            {aims_activity}.remote_data_id activity_id, -- This will be used as a ForeignKeyField, Django requires _id by default
            {aims_aidtypecategory}.code aidtypecategory_id, -- Another fk field
            {aims_transactionvalueusd}.dollars dollars
        FROM
            {aims_activity},
            {aims_transactionvalueusd},
            {iati_transaction},
            {aims_aidtype},
            {aims_aidtypecategory}
        WHERE
            --... --truncated for brevity
    '''.format(**tables)

    # id = models.AutoField(primary_key=True)
    activity = models.ForeignKey('aims.Activity')  # Represented as 'activity_id' in the query above
    aidtypecategory = models.ForeignKey(
        'aims.AidTypeCategory')  # Represented as 'aidtypecategory_id' in the query above
    dollars = models.FloatField()