django-mongo-backend 0.17

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Django backend for MongoDB (PoC Stage)

Django backend for MongoDB.

Supports:

• Column mappings to MongoDB documents
• Single table (collection) inheritance and single table OneToOne relationships
• Filters (filter/exclude)

Setup / Configuration

Not supported as primary database, as Django contrib apps rely on Integer primary keys in built in migrations (and because it is a use case that is not a priority at the moment).

# settings.py
DATABASES = {
    # or any other primary databse
    "default": {
        "ENGINE": "django.db.backends.sqlite3",
        "NAME": BASE_DIR / "db.sqlite3",
    },
    # mongodb database, Client constructor options are passe in 'CLIENT', the database name in 'NAME'
    "mongodb": {
        "ENGINE": "django_mongodb",
        "NAME": "django_mongodb",
        "CONN_MAX_AGE": 120,
        "CLIENT": {
            "host": os.environ.get("MONGODB_URL"),
        },
    },
}
# A database is required
DATABASE_ROUTERS = ["testproject.router.DatabaseRouter"]

Using the database in models requires a DatabaseRouter, which could look like this

class DatabaseRouter:
    def db_for_read(self, model, **hints):
        if model._meta.app_label == "mymongoapp":
            return "default"
        return "default"

    def db_for_write(self, model, **hints):
        if model._meta.app_label == "mymongoapp":
            return "default"
        return "default"

    def allow_relation(self, obj1, obj2, **hints):
        if obj1._meta.app_label == obj2._meta.app_label:
            return True
        return None

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        if app_label == "mymongoapp":
            # we are disabling migrations, as MongoDB is schema-less. Alerts, such as renaming fields, etc. are not supported
            return False
        return None

Finally we are going to change the default primary key of the app using MongoDB (if that is the case, otherwise add ObjectIdAutoField to the models, where you need it).

# apps.py
class TestappConfig(AppConfig):
    default_auto_field = "django_mongodb.models.ObjectIdAutoField"
    name = "mymongoapp"

Defining Models

A simple model, in an app, which has ObjectIdAutoField as default_auto_field

class MyModel(models.Model):
    json_field = JSONField()
    name = models.CharField(max_length=100)
    datetime_field = models.DateTimeField(auto_now_add=True)
    time_field = models.TimeField(auto_now_add=True)
    date_field = models.DateField(auto_now_add=True)

Single table inheritance

class SameTableChild(MyModel):
    my_model_ptr = models.OneToOneField(
        MyModel,
        on_delete=models.CASCADE,
        parent_link=True,
        related_name="same_table_child",
        # pointer to the primary key of the parent model
        db_column="_id",
    )
    extended = models.CharField(max_length=100)

    class Meta:
        # We are using the parent collection as db_table
        db_table = "mymongoapp_mymodel"

Single table OneToOne relationships