Read replica support

Issue

I had a simple DB router:

class ReadReplicaRouter:
    def db_for_read(self, model, **hints):
        """
        Return one of the replicas
        """
        return random.choice(["replica1", "replica2"])

    def db_for_write(self, model, **hints):
        # Always return the default database
        return "default"

This caused errors because the search_path for the read replica was never set, only the default database.

I saw #179 which allowed you to select which database you would like to operate on, but I believe this still only allows for 1 database

Related to: #243

My solution

For my project, I have subclassed TenantMainMiddleware and made a slight alteration to the process_request function, replacing

from django.db import connection
#...
connection.set_schema_to_public()
#...
connection.set_tenant(request.tenant)

With

from django.db import connections
#...
for con in connections:
    connections[con].set_schema_to_public()
#...
for con in connections:
    connections[con].set_tenant(request.tenant)

Suggestion

Is this something that is safe for all users? I’m happy to create a pull request, maybe with a setting with a list of names of database connections that would have their connections set?

Solution full code

from django.db import connections
from django_tenants.middleware import TenantMainMiddleware
from django_tenants.utils import get_tenant_domain_model


class ReadReplicaTenantMiddleware(TenantMainMiddleware):
    def process_request(self, request):
        # Connection needs first to be at the public schema, as this is where
        # the tenant metadata is stored.

        for con in connections:
            connections[con].set_schema_to_public()
        hostname = self.hostname_from_request(request)

        domain_model = get_tenant_domain_model()
        try:
            tenant = self.get_tenant(domain_model, hostname)
        except domain_model.DoesNotExist:
            return self.no_tenant_found(request, hostname)

        tenant.domain_url = hostname
        request.tenant = tenant
        for con in connections:
            connections[con].set_tenant(request.tenant)
        self.setup_url_routing(request)

[adnathanail]

@mmcclelland1002 great work on that PR! Are you able to show the code you’ve written to work with the EXTRA_SET_TENANT_METHOD_PATH feature?

[mmcclelland1002]

@adnathanail @dendrochronology I made a PR for this feature: https://github.com/django-tenants/django-tenants/pull/760 Please feel free to contribute and/or support this change to get merged in!