Database: Add patches and polyfills from application adapters

Sources: MLflow, LangChain, Singer/Meltano, rdflib-sqlalchemy

src/sqlalchemy_cratedb/support/__init__.py

@@ -1,5 +1,9 @@
 from sqlalchemy_cratedb.support.pandas import insert_bulk
+from sqlalchemy_cratedb.support.polyfill import check_uniqueness_factory
+from sqlalchemy_cratedb.support.util import refresh_table
 
 __all__ = [
+    check_uniqueness_factory,
     insert_bulk,
+    refresh_table,
 ]

src/sqlalchemy_cratedb/support/polyfill.py

@@ -0,0 +1,117 @@
+import sqlalchemy as sa
+from sqlalchemy.event import listen
+
+from sqlalchemy_cratedb.support.util import do_flush
+
+
+def polyfill_autoincrement_timestamp():
+    """
+    Configure SQLAlchemy model columns with an alternative to `autoincrement=True`.
+    Use the current timestamp instead.
+
+    This is used by CrateDB's MLflow adapter.
+
+    TODO: Maybe enable through a dialect parameter `crate_polyfill_autoincrement` or such.
+    """
+    import sqlalchemy.sql.schema as schema
+    from sqlalchemy import func
+
+    init_dist = schema.Column.__init__
+
+    def __init__(self, *args, **kwargs):
+        if "autoincrement" in kwargs:
+            del kwargs["autoincrement"]
+            if "default" not in kwargs:
+                kwargs["default"] = func.now()
+        init_dist(self, *args, **kwargs)
+
+    schema.Column.__init__ = __init__  # type: ignore[method-assign]
+
+
+def check_uniqueness_factory(sa_entity, *attribute_names):
+    """
+    Run a manual column value uniqueness check on a table, and raise an IntegrityError if applicable.
+
+    CrateDB does not support the UNIQUE constraint on columns. This attempts to emulate it.
+
+    https://github.com/crate/sqlalchemy-cratedb/issues/76
+
+    This is used by CrateDB's MLflow adapter.
+
+    TODO: Maybe enable through a dialect parameter `crate_polyfill_unique` or such.
+    """
+
+    # Synthesize a canonical "name" for the constraint,
+    # composed of all column names involved.
+    constraint_name: str = "-".join(attribute_names)
+
+    def check_uniqueness(mapper, connection, target):
+        from sqlalchemy.exc import IntegrityError
+
+        if isinstance(target, sa_entity):
+            # TODO: How to use `session.query(SqlExperiment)` here?
+            stmt = mapper.selectable.select()
+            for attribute_name in attribute_names:
+                stmt = stmt.filter(getattr(sa_entity, attribute_name) == getattr(target, attribute_name))
+            stmt = stmt.compile(bind=connection.engine)
+            results = connection.execute(stmt)
+            if results.rowcount > 0:
+                raise IntegrityError(
+                    statement=stmt,
+                    params=[],
+                    orig=Exception(
+                        f"DuplicateKeyException in table '{target.__tablename__}' " f"on constraint '{constraint_name}'"
+                    ),
+                )
+
+    return check_uniqueness
+
+
+def polyfill_refresh_after_dml_session(session: sa.orm.Session):
+    """
+    Run `REFRESH TABLE <tablename>` after each INSERT, UPDATE, and DELETE operation.
+
+    CrateDB is eventually consistent, i.e. write operations are not flushed to
+    disk immediately, so readers may see stale data. In a traditional OLTP-like
+    application, this is not applicable.
+
+    This SQLAlchemy extension makes sure that data is synchronized after each
+    operation manipulating data.
+
+    > `after_{insert,update,delete}` events only apply to the session flush operation
+    > and do not apply to the ORM DML operations described at ORM-Enabled INSERT,
+    > UPDATE, and DELETE statements. To intercept ORM DML events, use
+    > `SessionEvents.do_orm_execute().`
+    > -- https://docs.sqlalchemy.org/en/20/orm/events.html#sqlalchemy.orm.MapperEvents.after_insert
+
+    > Intercept statement executions that occur on behalf of an ORM Session object.
+    > -- https://docs.sqlalchemy.org/en/20/orm/events.html#sqlalchemy.orm.SessionEvents.do_orm_execute
+
+    > Execute after flush has completed, but before commit has been called.
+    > -- https://docs.sqlalchemy.org/en/20/orm/events.html#sqlalchemy.orm.SessionEvents.after_flush
+
+    This is used by CrateDB's LangChain adapter.
+
+    TODO: Maybe enable through a dialect parameter `crate_dml_refresh` or such.
+    """  # noqa: E501
+    listen(session, "after_flush", do_flush)
+
+
+def polyfill_refresh_after_dml_engine(engine: sa.engine.Engine):
+    def receive_after_execute(
+        conn: sa.engine.Connection, clauseelement, multiparams, params, execution_options, result
+    ):
+        """
+        Run a `REFRESH TABLE ...` command after each DML operation (INSERT, UPDATE, DELETE).
+
+        This is used by CrateDB's Singer/Meltano and `rdflib-sqlalchemy` adapters.
+        """
+
+        if isinstance(clauseelement, (sa.sql.Insert, sa.sql.Update, sa.sql.Delete)):
+            if not isinstance(clauseelement.table, sa.sql.Join):
+                full_table_name = f'"{clauseelement.table.name}"'
+                if clauseelement.table.schema is not None:
+                    full_table_name = f'"{clauseelement.table.schema}".' + full_table_name
+                conn.execute(sa.text(f'REFRESH TABLE {full_table_name};'))
+
+    sa.event.listen(engine, "after_execute", receive_after_execute)

src/sqlalchemy_cratedb/support/util.py

@@ -0,0 +1,29 @@
+import itertools
+import typing as t
+
+import sqlalchemy as sa
+from sqlalchemy.orm import DeclarativeBase
+
+
+def refresh_table(connection, target: t.Union[str, DeclarativeBase]):
+    """
+    Invoke a `REFRESH TABLE` statement.
+    """
+    if isinstance(target, DeclarativeBase):
+        sql = f"REFRESH TABLE {target.__tablename__}"
+    else:
+        sql = f"REFRESH TABLE {target}"
+    connection.execute(sa.text(sql))
+
+
+def do_flush(session, flush_context):
+    """
+    Invoke a `REFRESH TABLE` statement on each table entity flagged as "dirty".
+
+    SQLAlchemy event handler for the 'after_flush' event,
+    invoking `REFRESH TABLE` on each table which has been modified.
+    """
+    dirty_entities = itertools.chain(session.new, session.dirty, session.deleted)
+    dirty_classes = {entity.__class__ for entity in dirty_entities}
+    for class_ in dirty_classes:
+        refresh_table(session, class_)

tests/integration.py

@@ -124,6 +124,7 @@ def drop_tables():
         "DROP TABLE IF EXISTS archived_tasks",
         "DROP TABLE IF EXISTS characters",
         "DROP TABLE IF EXISTS cities",
+        "DROP TABLE IF EXISTS foobar",
         "DROP TABLE IF EXISTS locations",
         "DROP BLOB TABLE IF EXISTS myfiles",
         "DROP TABLE IF EXISTS search",

tests/test_support_polyfill.py

@@ -0,0 +1,49 @@
+import pytest
+import sqlalchemy as sa
+from sqlalchemy.event import listen
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.orm import sessionmaker
+
+try:
+    from sqlalchemy.orm import declarative_base
+except ImportError:
+    from sqlalchemy.ext.declarative import declarative_base
+
+from sqlalchemy_cratedb.support import check_uniqueness_factory
+
+
+def test_check_uniqueness_factory(cratedb_service):
+    """
+    An integration test validating basic synthetic UNIQUE constraints.
+
+    https://github.com/crate/sqlalchemy-cratedb/issues/76
+    """
+
+    engine = cratedb_service.database.engine
+    session = sessionmaker(bind=engine)()
+    Base = declarative_base()
+
+    # Define DDL.
+    class FooBar(Base):
+        __tablename__ = 'foobar'
+        id = sa.Column(sa.String, primary_key=True)
+        name = sa.Column(sa.String)
+
+    # Add synthetic UNIQUE constraint on `name` column.
+    listen(FooBar, "before_insert", check_uniqueness_factory(FooBar, "name"))
+
+    Base.metadata.drop_all(engine, checkfirst=True)
+    Base.metadata.create_all(engine, checkfirst=True)
+
+    # Insert baseline record.
+    foo_item = FooBar(id="foo", name="foo")
+    session.add(foo_item)
+    session.commit()
+    session.execute(sa.text("REFRESH TABLE foobar"))
+
+    # Insert second record, violating the uniqueness constraint.
+    bar_item = FooBar(id="bar", name="foo")
+    session.add(bar_item)
+    with pytest.raises(IntegrityError) as ex:
+        session.commit()
+    assert ex.match("DuplicateKeyException in table 'foobar' on constraint 'name'")