db_composition.py

import abc
import unittest

import six

### base stuff ###
@six.add_metaclass(abc.ABCMeta)
class API(object):
    @abc.abstractproperty
    def backend(self):
        """Backend to use for common ops"""

    @abc.abstractmethod
    def create_transaction(self):
        """Create transaction"""

    def db_add(self, *args, **kwargs):
        return self.backend.db_add(*args, **kwargs)

### Backend-specific, schema-agnostic impl stuff ###
class IdlDb(object):
    def db_add(self, *args, **kwargs):
        return IdlDb

class CliDb(object):
    def db_add(self, *args, **kwargs):
        return CliDb

### Open_vSwitch schema stuff ###
@six.add_metaclass(abc.ABCMeta)
class VsctlAPI(API):
    @abc.abstractmethod
    def add_bridge(self, br):
        """Add a bridge"""

# We could use composition to avoid multiple-inheritance
class VsctlIdlImpl(VsctlAPI):
    backend = IdlDb()

    def create_transaction(self):
        return True

    def add_bridge(self, br):
        return True

class VsctlCliImpl(VsctlAPI):
    backend = CliDb()

    def create_transaction(self):
        return True

    def add_bridge(self, br):
        return True

### OVN_Northbound schema stuff ###
@six.add_metaclass(abc.ABCMeta)
class OVNNbAPI(API):
    @abc.abstractmethod
    def acl_add(self, **acl_args):
        """Add an ACL"""

class OvnNbIdlImpl(OVNNbAPI):
    backend = IdlDb()

    def create_transaction(self):
        return True

    def acl_add(self, **acl_args):
        return True

class OvnNbCliImpl(OVNNbAPI):
    backend = CliDb()

    def create_transaction(self):
        return True

    def acl_add(self, **acl_args):
        return True

class ApiTest(unittest.TestCase):
    impl_map = {
        VsctlIdlImpl: IdlDb,
        VsctlCliImpl: CliDb,
        OvnNbIdlImpl: IdlDb,
        OvnNbCliImpl: CliDb,
    }

    def test_impl_db_usage(self):
        for impl, db in self.impl_map.items():
            i = impl()
            self.assertEqual(i.db_add(), db)

db_mixins.py

import abc
import unittest

import six

### base stuff ###
@six.add_metaclass(abc.ABCMeta)
class API(object):
    @abc.abstractmethod
    def create_transaction(self):
        """Create transaction"""

    @abc.abstractmethod
    def db_add(self, *args, **kwargs):
        """Add object to db"""

### Backend-specific, schema-agnostic impl stuff ###
class IdlDb(API):
    def db_add(self, *args, **kwargs):
        return IdlDb

class CliDb(API):
    def db_add(self, *args, **kwargs):
        return CliDb

### Open_vSwitch schema stuff ###
@six.add_metaclass(abc.ABCMeta)
class VsctlAPI(API):
    @abc.abstractmethod
    def add_bridge(self, br):
        """Add a bridge"""

# how would we do this with single-inheritance?
# we need the schema-specific API and the schema-agnostic Db ops
# we can't add the schema-agnostic stuff to the VsctlAPI
class VsctlIdlImpl(VsctlAPI, IdlDb):
    def create_transaction(self):
        return True

    def add_bridge(self, br):
        return True

class VsctlCliImpl(VsctlAPI, CliDb):
    def create_transaction(self):
        return True

    def add_bridge(self, br):
        return True

### OVN_Northbound schema stuff ###
@six.add_metaclass(abc.ABCMeta)
class OVNNbAPI(API):
    @abc.abstractmethod
    def acl_add(self, **acl_args):
        """Add an ACL"""

class OvnNbIdlImpl(OVNNbAPI, IdlDb):
    def create_transaction(self):
        return True

    def acl_add(self, **acl_args):
        return True

class OvnNbCliImpl(OVNNbAPI, CliDb):
    def create_transaction(self):
        return True

    def acl_add(self, **acl_args):
        return True

class ApiTest(unittest.TestCase):
    impl_map = {
        VsctlIdlImpl: IdlDb,
        VsctlCliImpl: CliDb,
        OvnNbIdlImpl: IdlDb,
        OvnNbCliImpl: CliDb,
    }

    def test_impl_db_usage(self):
        for impl, db in self.impl_map.items():
            i = impl()
            self.assertEqual(i.db_add(), db)