from django.db import DEFAULT_DB_ALIAS

class TestRouter:

    """

    Vaguely behave like primary/replica, but the databases aren't assumed to

    propagate changes.

    """

    def db_for_read(self, model, instance=None, **hints):

        if instance:

            return instance._state.db or "other"

        return "other"

    def db_for_write(self, model, **hints):

        return DEFAULT_DB_ALIAS

    def allow_relation(self, obj1, obj2, **hints):

        return obj1._state.db in ("default", "other") and obj2._state.db in (

            "default",

            "other",

        )

    def allow_migrate(self, db, app_label, **hints):

        return True

class AuthRouter:

    """

    Control all database operations on models in the contrib.auth application.

    """

    def db_for_read(self, model, **hints):

        "Point all read operations on auth models to 'default'"

        if model._meta.app_label == "auth":

            # We use default here to ensure we can tell the difference

            # between a read request and a write request for Auth objects

            return "default"

        return None

    def db_for_write(self, model, **hints):

        "Point all operations on auth models to 'other'"

        if model._meta.app_label == "auth":

            return "other"

        return None

    def allow_relation(self, obj1, obj2, **hints):

        "Allow any relation if a model in Auth is involved"

        return obj1._meta.app_label == "auth" or obj2._meta.app_label == "auth" or None

    def allow_migrate(self, db, app_label, **hints):

        "Make sure the auth app only appears on the 'other' db"

        if app_label == "auth":

            return db == "other"

        return None

class WriteRouter:

    # A router that only expresses an opinion on writes

    def db_for_write(self, model, **hints):

        return "writer"