Error when using multiple Bds in Django

Question

Hello

I’m studying how to add two databases in Django and am finding a problem.

When I use the using in the list method, it can use the database chosen and lists the clients in the template.

def listar_clientes():
    clientes = Cliente.objects.using('leitura').all()
    return clientes

But when using the router find next problem:

raise ImproperlyConfigured("settings.DATABASES is improperly configured. 
"
django.core.exceptions.ImproperlyConfigured: settings.DATABASES is improperly configured. Please supply the ENGINE value. Check settings doc
umentation for more details.

Code of the Router:

class Router(object):
    def db_for_read(self, models, **hints):
        return 'leitura'

    def db_for_write(self, models, **hints):
        return 'escrita'

py Settings.:

....


DATABASES = {
    'default': {},
    'escrita': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'tw_django_orm_escrita',
        'USER': 'root',
        'PASSWORD': '1234',
        'HOST': 'localhost',
        'PORT': '3306'
    },
    'leitura': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'tw_django_orm_leitura',
        'USER': 'root',
        'PASSWORD': '1234',
        'HOST': 'localhost',
        'PORT': '3306'
    },
}

DATABASES_ROUTERS = ['clientes.router.Router']

....

I need some help to solve this problem!!

Answer 1

You need to remove the 'default': {},. He’s trying to find the configuration of "ENGINE" in that dictionary and can’t.

I suggest you leave the default as your writing database and create one with the replica name where the replica is the read.

I like working with the following configuration for production:

DATABASES = {
    "default": {
        "ENGINE": os.getenv("DB_ENGINE", "django.db.backends.sqlite3"),
        "NAME": os.getenv("DB_DATABASE", os.path.join(BASE_DIR, "db.sqlite3")),
        "USER": os.environ.get("DB_USER"),
        "HOST": os.environ.get("DB_HOST"),
        "PORT": os.environ.get("DB_PORT"),
        "PASSWORD": os.environ.get("DB_PASSWORD"),
    }
}

DATABASES["default"]["CONN_MAX_AGE"] = int(os.getenv("DB_CONN_MAX_AGE", 0))  # type: ignore

if os.getenv("USE_REPLICA"):
    DATABASES["replica"] = {
        "ENGINE": os.getenv("DB_ENGINE_REPLICA"),
        "NAME": os.getenv("DB_DATABASE_REPLICA"),
        "USER": os.getenv("DB_USER_REPLICA"),
        "HOST": os.getenv("DB_HOST_REPLICA"),
        "PORT": os.getenv("DB_PORT_REPLICA"),
        "PASSWORD": os.getenv("DB_PASSWORD_REPLICA"),
    }
    DATABASES["replica"]["CONN_MAX_AGE"] = int(os.getenv("DB_CONN_MAX_AGE_REPLICA", 0))  # type: ignore
    DATABASE_ROUTERS = ["MY_PROJECT.support.db_routing.DatabaseRouter"]

My router is:

class DatabaseRouter:
    """
    A router to control all database operations on models in the
    auth application.
    """

    def db_for_read(self, model, **hints):
        """
        Always read from REPLICA database
        """
        return "replica"

    def db_for_write(self, model, **hints):
        """
        Always write to DEFAULT database
        """
        return "default"

    def allow_relation(self, obj1, obj2, **hints):
        """
        Objects from REPLICA and DEFAULT are de same, then True always
        """
        return True

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        """
        Only DEFAULT database
        """
        return db == "default"

If you want to keep your setup without the default, you must configure all class methods DatabaseRouter default return by default. Like def allow_migrate(self, db, app_label, model_name=None, **hints):

The official documentation for consultation is: Multiple Databases