Doing this we're able to load our example model into the admin, view it and all related bits and even save without issue. There are some issues when using foreign keys from separate databases in list views in the admin.
Most of this is documented at https://docs.djangoproject.com/en/3.1/topics/db/multi-db/. We've just modified it a bit so things live in settings.
Names for things might seem weird because we've changed them to protect the innocent...
| # oracle_db1/routers.py (gists don't like slashes) | |
| from django.conf import settings | |
| class OracleDb1Router: | |
| """Oracle db1 schema rules for legacy DB. | |
| Avoid read/write/migrate for apps using db1 schema unless we are also | |
| trying to use the 'db1' DB as defined in settings. | |
| When we leave a method out or return "None" we are allowing the default | |
| routing to take over as defined in django.db.utils.ConnectionRouter. | |
| More: https://docs.djangoproject.com/en/3.0/topics/db/multi-db/ | |
| """ | |
| def _db_for_action(self, model, **hints): | |
| """Route to our database if one of our apps.""" | |
| if model._meta.app_label in settings.ORACLE_DB1_ROUTER_APP_LABELS: | |
| return settings.ORACLE_DB1_ROUTER_DATABASE_NAME | |
| return None | |
| db_for_read = _db_for_action | |
| db_for_write = _db_for_action | |
| def allow_migrate(self, db, app_label, model_name=None, **hints): | |
| """Only allow migration for our apps in the db1 db/schema. | |
| This will only pass with "--database=db1" on your migration | |
| command(s) on the CLI. | |
| """ | |
| # If in our DB/schema, only migrate our apps (block django_* bits) | |
| if db == settings.ORACLE_DB1_ROUTER_DATABASE_NAME: | |
| return app_label in settings.ORACLE_DB1_ROUTER_APP_LABELS | |
| # If one of our apps, only migrate within our DB/schema | |
| if app_label in settings.ORACLE_DB1_ROUTER_APP_LABELS: | |
| return db == settings.ORACLE_DB1_ROUTER_DATABASE_NAME | |
| return None | |
| def allow_relation(self, obj1, obj2, **hints): | |
| db_set = { | |
| settings.ORACLE_DB1_ROUTER_DATABASE_NAME, | |
| *settings.ORACLE_DB1_ROUTER_ALLOWED_RELATIONS, | |
| } | |
| if obj1._state.db in db_set and obj2._state.db in db_set: | |
| return True | |
| return None |
| # oracle_db2/models.py (gists don't like slashes) | |
| from django.db import models | |
| class SomeModel(models.Model): | |
| db1_field = models.ForeignKey('oracle_db2.Directory', models.DO_NOTHING, db_column='db1_field') | |
| class Meta: | |
| db_table = 'some_table' | |
| managed = False |
| # oracle_db2/routers.py (gists don't like slashes) | |
| from django.conf import settings | |
| class OracleDb2Router: | |
| """Oracle db2 schema rules for legacy DB. | |
| Avoid read/write/migrate for apps using db2 schema unless we are also | |
| trying to use the 'db2' DB as defined in settings. | |
| When we leave a method out or return "None" we are allowing the default | |
| routing to take over as defined in django.db.utils.ConnectionRouter. | |
| More: https://docs.djangoproject.com/en/3.0/topics/db/multi-db/ | |
| """ | |
| def _db_for_action(self, model, **hints): | |
| """Route to our database if one of our apps.""" | |
| if model._meta.app_label in settings.ORACLE_DB2_ROUTER_APP_LABELS: | |
| return settings.ORACLE_DB2_ROUTER_DATABASE_NAME | |
| return None | |
| db_for_read = _db_for_action | |
| db_for_write = _db_for_action | |
| def allow_migrate(self, db, app_label, model_name=None, **hints): | |
| """Only allow migration for our apps in the db2 db/schema. | |
| This will only pass with "--database=db2" on your migration | |
| command(s) on the CLI. | |
| """ | |
| # If in our DB/schema, only migrate our apps (block django_* bits) | |
| if db == settings.ORACLE_DB2_ROUTER_DATABASE_NAME: | |
| return app_label in settings.ORACLE_DB2_ROUTER_APP_LABELS | |
| # If one of our apps, only migrate within our DB/schema | |
| if app_label in settings.ORACLE_DB2_ROUTER_APP_LABELS: | |
| return db == settings.ORACLE_DB2_ROUTER_DATABASE_NAME | |
| return None | |
| def allow_relation(self, obj1, obj2, **hints): | |
| db_set = { | |
| settings.ORACLE_DB2_ROUTER_DATABASE_NAME, | |
| *settings.ORACLE_DB2_ROUTER_ALLOWED_RELATIONS, | |
| } | |
| if obj1._state.db in db_set and obj2._state.db in db_set: | |
| return True | |
| return None |
| # DATABASE | |
| # ------------------------------------------------------------------------------ | |
| # Database: OracleDb1Router: Apps using our schema. | |
| ORACLE_DB1_ROUTER_APP_LABELS = {'oracle_db1', } | |
| # Database: OracleDb1Router: Prefix for django_migrations table. | |
| ORACLE_DB1_MIGRATIONS_PREFIX = 'proj_foo_' | |
| # Database: OracleDb1Router: DB name from settings.DATABASES. | |
| ORACLE_DB1_ROUTER_DATABASE_NAME = 'db1' | |
| # Database: OracleDb2Router: Apps using our schema. | |
| ORACLE_DB2_ROUTER_APP_LABELS = {'oracle_db2', } | |
| # Database: OracleDb2Router: Prefix for django_migrations table. | |
| ORACLE_DB2_MIGRATIONS_PREFIX = 'proj_foo' | |
| # Database: OracleDb2Router: DB name from settings.DATABASES. | |
| ORACLE_DB2_ROUTER_DATABASE_NAME = 'db2' | |
| # Database: OracleDb1Router: Allowed relations | |
| ORACLE_DB1_ROUTER_ALLOWED_RELATIONS = {ORACLE_DB2_ROUTER_DATABASE_NAME, } | |
| # Database: OracleDb2Router: Allowed relations | |
| ORACLE_DB2_ROUTER_ALLOWED_RELATIONS = {ORACLE_DB1_ROUTER_DATABASE_NAME, } | |
| # Database: Core | |
| DATABASES = { | |
| 'default': { | |
| 'ENGINE': 'django.db.backends.oracle', | |
| 'HOST': '', | |
| 'NAME': env('ORACLE_DSN'), | |
| 'PASSWORD': env('ORACLE_PROJ_FOO_PASSWORD'), | |
| 'PORT': '', | |
| 'USER': env('ORACLE_PROJ_FOO_USER'), | |
| }, | |
| ORACLE_DB1_ROUTER_DATABASE_NAME: { | |
| 'ENGINE': 'django.db.backends.oracle', | |
| 'HOST': '', | |
| 'NAME': env('ORACLE_DSN'), | |
| 'PASSWORD': env('ORACLE_DB1_PASSWORD'), | |
| 'PORT': '', | |
| 'USER': env('ORACLE_DB1_USER'), | |
| }, | |
| ORACLE_DB2_ROUTER_DATABASE_NAME: { | |
| 'ENGINE': 'django.db.backends.oracle', | |
| 'HOST': '', | |
| 'NAME': env('ORACLE_DSN'), | |
| 'PASSWORD': env('ORACLE_DB2_PASSWORD'), | |
| 'PORT': '', | |
| 'USER': env('ORACLE_DB2_USER'), | |
| }, | |
| } | |
| # Database: Routers for which of our DBs to use for what. | |
| DATABASE_ROUTERS = [ | |
| 'proj_foo.oracle_db1.routers.OracleDb1Router', | |
| 'proj_foo.oracle_db2.routers.OracleDb2Router', | |
| ] |