Draft

src/tribler/core/components/database/database_component.py

@@ -15,7 +15,7 @@ async def run(self):
         if self.session.config.gui_test_mode:
             db_path = ":memory:"
 
-        self.db = TriblerDatabase(str(db_path), create_tables=True)
+        self.db = TriblerDatabase(str(db_path))
 
     async def shutdown(self):
         await super().shutdown()

src/tribler/core/components/database/db/layers/tests/test_knowledge_data_access_layer.py

@@ -14,13 +14,19 @@
 # pylint: disable=protected-access
 class TestKnowledgeAccessLayer(TestKnowledgeAccessLayerBase):
     @patch.object(TrackedDatabase, 'generate_mapping')
+    @patch.object(TriblerDatabase, 'fill_default_data', Mock())
     def test_constructor_create_tables_true(self, mocked_generate_mapping: Mock):
-        TriblerDatabase(':memory:')
+        """ Test that constructor of TriblerDatabase calls TrackedDatabase.generate_mapping with create_tables=True"""
+        TriblerDatabase()
+
         mocked_generate_mapping.assert_called_with(create_tables=True)
 
     @patch.object(TrackedDatabase, 'generate_mapping')
+    @patch.object(TriblerDatabase, 'fill_default_data', Mock())
     def test_constructor_create_tables_false(self, mocked_generate_mapping: Mock):
-        TriblerDatabase(':memory:', create_tables=False)
+        """ Test that constructor of TriblerDatabase calls TrackedDatabase.generate_mapping with create_tables=False"""
+        TriblerDatabase(create_tables=False)
+
         mocked_generate_mapping.assert_called_with(create_tables=False)
 
     @db_session
@@ -245,7 +251,7 @@ def test_get_objects_removed(self):
         )
 
         self.add_operation(self.db, subject='infohash1', predicate=ResourceType.TAG, obj='tag2', peer=b'4',
-                                        operation=Operation.REMOVE)
+                           operation=Operation.REMOVE)
 
         assert self.db.knowledge.get_objects(subject='infohash1', predicate=ResourceType.TAG) == ['tag1']
 

src/tribler/core/components/database/db/tests/test_tribler_database.py

@@ -1,3 +1,4 @@
+import pytest
 from ipv8.test.base import TestBase
 from pony.orm import db_session
 
@@ -37,8 +38,10 @@ def dump_db(self):
     @db_session
     def test_set_misc(self):
         """Test that set_misc works as expected"""
-        self.db.set_misc(key='key', value='value')
-        assert self.db.get_misc(key='key') == 'value'
+        self.db.set_misc(key='string', value='value')
+        self.db.set_misc(key='integer', value=1)
+        assert self.db.get_misc(key='string') == 'value'
+        assert self.db.get_misc(key='integer') == '1'
 
     @db_session
     def test_non_existent_misc(self):
@@ -48,3 +51,20 @@ def test_non_existent_misc(self):
 
         # A value if the key does exist
         assert self.db.get_misc(key='non existent', default=42) == 42
+
+    @db_session
+    def test_default_version(self):
+        """ Test that the default version is equal to `CURRENT_VERSION`"""
+        assert self.db.version == TriblerDatabase.CURRENT_VERSION
+
+    @db_session
+    def test_version_getter_and_setter(self):
+        """ Test that the version getter and setter work as expected"""
+        self.db.version = 42
+        assert self.db.version == 42
+
+    @db_session
+    def test_version_getter_unsupported_type(self):
+        """ Test that the version getter raises a TypeError if the type is not supported"""
+        with pytest.raises(TypeError):
+            self.db.version = 'string'

src/tribler/core/components/database/db/tribler_database.py

@@ -1,14 +1,20 @@
 import logging
+import os
 from typing import Any, Optional
 
 from pony import orm
 
 from tribler.core.components.database.db.layers.health_data_access_layer import HealthDataAccessLayer
 from tribler.core.components.database.db.layers.knowledge_data_access_layer import KnowledgeDataAccessLayer
-from tribler.core.utilities.pony_utils import TrackedDatabase, get_or_create
+from tribler.core.utilities.pony_utils import TrackedDatabase, db_session, get_or_create
+
+MEMORY = ':memory:'
 
 
 class TriblerDatabase:
+    CURRENT_VERSION = 1
+    _SCHEME_VERSION = 'scheme_version'
+
     def __init__(self, filename: Optional[str] = None, *, create_tables: bool = True, **generate_mapping_kwargs):
         self.instance = TrackedDatabase()
 
@@ -25,21 +31,31 @@ def __init__(self, filename: Optional[str] = None, *, create_tables: bool = True
         self.TorrentHealth = self.health.TorrentHealth
         self.Tracker = self.health.Tracker
 
-        self.instance.bind('sqlite', filename or ':memory:', create_db=True)
+        filename = filename or MEMORY
+        db_does_not_exist = filename == MEMORY or not os.path.isfile(filename)
+
+        self.instance.bind('sqlite', filename, create_db=db_does_not_exist)
         generate_mapping_kwargs['create_tables'] = create_tables
         self.instance.generate_mapping(**generate_mapping_kwargs)
         self.logger = logging.getLogger(self.__class__.__name__)
 
+        if db_does_not_exist:
+            self.fill_default_data()
+
     @staticmethod
     def define_binding(db):
         """ Define common bindings"""
-
-        class Misc(db.Entity):  # pylint: disable=unused-variable
+        class Misc(db.Entity):
             name = orm.PrimaryKey(str)
             value = orm.Optional(str)
 
         return Misc
 
+    @db_session
+    def fill_default_data(self):
+        self.logger.info('Filling the DB with the default data')
+        self.set_misc(self._SCHEME_VERSION, self.CURRENT_VERSION)
+
     def get_misc(self, key: str, default: Optional[str] = None) -> Optional[str]:
         data = self.Misc.get(name=key)
         return data.value if data else default
@@ -48,5 +64,18 @@ def set_misc(self, key: str, value: Any):
         key_value = get_or_create(self.Misc, name=key)
         key_value.value = str(value)
 
+    @property
+    def version(self) -> int:
+        """ Get the database version"""
+        return int(self.get_misc(key=self._SCHEME_VERSION, default=0))
+
+    @version.setter
+    def version(self, value: int):
+        """ Set the database version"""
+        if not isinstance(value, int):
+            raise TypeError('DB version should be integer')
+
+        self.set_misc(key=self._SCHEME_VERSION, value=value)
+
     def shutdown(self) -> None:
         self.instance.disconnect()

src/tribler/core/upgrade/tribler_db/conftest.py

@@ -0,0 +1,18 @@
+import pytest
+
+from tribler.core.components.database.db.tribler_database import TriblerDatabase
+from tribler.core.upgrade.tribler_db.migration_chain import TriblerDatabaseMigrationChain
+from tribler.core.utilities.path_util import Path
+from tribler.core.utilities.simpledefs import STATEDIR_DB_DIR
+
+
+# pylint: disable=redefined-outer-name
+
+
+@pytest.fixture
+def migration_chain(tmpdir):
+    """ Create an empty migration chain with an empty database."""
+    db_file_name = Path(tmpdir) / STATEDIR_DB_DIR / 'tribler.db'
+    db_file_name.parent.mkdir()
+    TriblerDatabase(filename=str(db_file_name))
+    return TriblerDatabaseMigrationChain(state_dir=Path(tmpdir), chain=[])

src/tribler/core/upgrade/tribler_db/decorator.py

@@ -0,0 +1,51 @@
+import functools
+import logging
+from typing import Callable, Optional
+
+from tribler.core.components.database.db.tribler_database import TriblerDatabase
+from tribler.core.utilities.pony_utils import db_session
+
+MIGRATION_METADATA = "_tribler_db_migration"
+
+logger = logging.getLogger('Migration (TriblerDB)')
+
+
+def migration(execute_only_if_version: int):
+    """ Decorator for migration functions.
+
+    The migration executes in the single transaction. If the migration fails, the transaction is rolled back.
+    The decorator also sets the metadata attribute to the decorated function. It could be checked by
+    calling the `has_migration_metadata` function.
+
+    After the successful migration, db version is set to the value equal to `execute_only_if_version + 1`.
+
+    Args:
+        execute_only_if_version: Execute the migration only if the current db version is equal to this value.
+    """
+
+    def decorator(func):
+        @functools.wraps(func)
+        @db_session
+        def wrapper(db: TriblerDatabase, **kwargs):
+            target_version = execute_only_if_version
+            if target_version != db.version:
+                logger.info(
+                    f"Function {func.__name__} is not executed because DB version is not equal to {target_version}. "
+                    f"The current db version is {db.version}"
+                )
+                return None
+
+            result = func(db, **kwargs)
+            db.version = target_version + 1
+
+            return result
+
+        setattr(wrapper, MIGRATION_METADATA, {})
+        return wrapper
+
+    return decorator
+
+
+def has_migration_metadata(f: Callable):
+    """ Check if the function has migration metadata."""
+    return hasattr(f, MIGRATION_METADATA)

src/tribler/core/upgrade/tribler_db/migration_chain.py

@@ -0,0 +1,53 @@
+import logging
+from typing import Callable, Iterator, List, Optional
+
+from tribler.core.components.database.db.tribler_database import TriblerDatabase
+from tribler.core.upgrade.tribler_db.decorator import has_migration_metadata
+from tribler.core.upgrade.tribler_db.scheme_migrations.scheme_migration_0 import scheme_migration_0
+from tribler.core.utilities.path_util import Path
+from tribler.core.utilities.simpledefs import STATEDIR_DB_DIR
+
+
+class TriblerDatabaseMigrationChain:
+    """ A chain of migrations that can be executed on a TriblerDatabase.
+
+    To create a new migration, create a new function and decorate it with the `migration` decorator. Then add it to
+    the `DEFAULT_CHAIN` list.
+    """
+
+    DEFAULT_CHAIN = [
+        scheme_migration_0,
+        # add your migration here
+    ]
+
+    def __init__(self, state_dir: Path, chain: Optional[List[Callable]] = None):
+        self.logger = logging.getLogger(self.__class__.__name__)
+        self.state_dir = state_dir
+
+        db_path = self.state_dir / STATEDIR_DB_DIR / 'tribler.db'
+        self.logger.info(f'Tribler DB path: {db_path}')
+        self.db = TriblerDatabase(str(db_path), check_tables=False) if db_path.is_file() else None
+
+        self.migrations = chain or self.DEFAULT_CHAIN
+
+    def execute(self) -> bool:
+        """ Execute all migrations in the chain.
+
+        Returns: True if all migrations were executed successfully, False otherwise.
+        An exception in any of the migrations will halt the execution chain and be re-raised.
+        """
+
+        if not self.db:
+            return False
+
+        for _ in self.steps():
+            ...
+
+        return True
+
+    def steps(self) -> Iterator:
+        """ Execute migrations step by step."""
+        for m in self.migrations:
+            if not has_migration_metadata(m):
+                raise NotImplementedError(f'The migration {m} should have `migration` decorator')
+            yield m(self.db, state_dir=self.state_dir)

src/tribler/core/upgrade/tribler_db/scheme_migrations/scheme_migration_0.py

@@ -0,0 +1,23 @@
+from tribler.core.components.database.db.tribler_database import TriblerDatabase
+from tribler.core.upgrade.tribler_db.decorator import migration
+
+
+@migration(execute_only_if_version=0)
+def scheme_migration_0(db: TriblerDatabase, **kwargs):  # pylint: disable=unused-argument
+    """ "This is initial migration, placed here primarily for demonstration purposes.
+    It doesn't do anything except set the database version to `1`.
+
+    For upcoming migrations, there are some guidelines:
+    1. functions should contain a single parameter, `db: TriblerDatabase`,
+    2. they should apply the `@migration` decorator.
+
+
+    Utilizing plain SQL (as seen in the example below) is considered good practice since it helps prevent potential
+    inconsistencies in DB schemes in the future (model versions preceding the current one may differ from it).
+    For more information see: https://github.com/Tribler/tribler/issues/7382
+
+    The example of a migration:
+
+        db.execute('ALTER TABLE "TorrentState" ADD "has_data" BOOLEAN DEFAULT 0')
+        db.execute('UPDATE "TorrentState" SET "has_data" = 1 WHERE last_check > 0')
+    """

src/tribler/core/upgrade/tribler_db/scheme_migrations/tests/test_scheme_migration_0.py

@@ -0,0 +1,13 @@
+from tribler.core.upgrade.tribler_db.migration_chain import TriblerDatabaseMigrationChain
+from tribler.core.upgrade.tribler_db.scheme_migrations.scheme_migration_0 import scheme_migration_0
+from tribler.core.utilities.pony_utils import db_session
+
+
+@db_session
+def test_scheme_migration_0(migration_chain: TriblerDatabaseMigrationChain):
+    """ Test that the scheme_migration_0 changes the database version to 1. """
+    migration_chain.db.version = 0
+    migration_chain.migrations = [scheme_migration_0]
+
+    assert migration_chain.execute()
+    assert migration_chain.db.version == 1

src/tribler/core/upgrade/tribler_db/tests/test_decorator.py

@@ -0,0 +1,56 @@
+from unittest.mock import Mock
+
+import pytest
+
+from tribler.core.upgrade.tribler_db.decorator import has_migration_metadata, migration
+
+
+def test_migration_execute_only_if_version():
+    """ Test that migration is executed only if the version of the database is equal to the specified one."""
+
+    @migration(execute_only_if_version=1)
+    def test(_: Mock):
+        return True
+
+    assert test(Mock(version=1))
+    assert not test(Mock(version=2))
+
+
+def test_migration_set_next_version():
+    """ Test that the version of the database is set to the next one after the successful migration."""
+
+    @migration(execute_only_if_version=1)
+    def test(_: Mock):
+        return True
+
+    db = Mock(version=1)
+    assert test(db)
+    assert db.version == 2
+
+
+def test_migration_set_next_version_raise_an_exception():
+    """ Test that if an exception is raised during the migration, the version of the database is not changed."""
+
+    @migration(execute_only_if_version=1)
+    def test(_: Mock):
+        raise TypeError
+
+    db = Mock(version=1)
+    with pytest.raises(TypeError):
+        test(db)
+
+    assert db.version == 1
+
+
+def test_set_metadata():
+    """ Test that the metadata flag is set."""
+
+    @migration(execute_only_if_version=1)
+    def simple_migration(_: Mock):
+        ...
+
+    def no_migration(_: Mock):
+        ...
+
+    assert has_migration_metadata(simple_migration)
+    assert not has_migration_metadata(no_migration)