Add support for identity columns

README.rst

@@ -318,6 +318,22 @@ insert/upsert/merge implementation is available in SQLAlchemy (see https://githu
         statement upsert(stuff).values(id=1, data="some").filter_by(id=1)
         conn.execute(statement)
 
+Identity
+~~~~~~~~
+Identity columns are fully supported but not reflection of those.
+
+Auto-increment
+~~~~~~~~~~~~~~
+SAP HANA only supports auto-increment with identity columns, therefore an identity will be rendered
+if needed. This means that the  the following constructs are equivalent:
+
+* ``Column('some', Integer, autoincrement=True)``
+* ``Column('some', Integer, Identity, autoincrement=True)``
+* ``Column('some', Integer, Identity, autoincrement=True)``
+
+Note, that for ``autoincrement=True`` a post-execute statement execution is needed to fetch the
+inserted identity value which might affect performance.
+
 Alembic
 -------
 The sqlalchemy-hana dialect also contains a dialect for ``alembic``.
@@ -349,32 +365,6 @@ error and raise a more specific exception if possible.
         # if you reach this line, either the wrapped error of DBAPIError was not a hdbcli error
         # of no more specific exception was found
 
-Cookbook
---------
-
-IDENTITY Feature
-~~~~~~~~~~~~~~~~
-SAP HANA also comes with an option to have an ``IDENTITY`` column which can also be used to create
-new primary key values for integer-based primary key columns.
-Built-in support for rendering of ``IDENTITY`` is not available yet, however the following compilation
-hook may be used to make use of
-the IDENTITY feature.
-
-.. code-block:: python
-
-    from sqlalchemy.schema import CreateColumn
-    from sqlalchemy.ext.compiler import compiles
-
-    @compiles(CreateColumn, 'hana')
-    def use_identity(element, compiler, **kw):
-        text = compiler.visit_create_column(element, **kw)
-        text = text.replace('NOT NULL', 'NOT NULL GENERATED BY DEFAULT AS IDENTITY')
-        return text
-
-    t = Table('t', meta, Column('id', Integer, primary_key=True), Column('data', String))
-
-    t.create(engine)
-
 Development Setup
 -----------------
 We recommend the usage of ``pyenv`` to install a proper 3.11 python version for development.

sqlalchemy_hana/dialect.py

@@ -11,6 +11,7 @@
 import sqlalchemy
 from sqlalchemy import (
     Computed,
+    Identity,
     Integer,
     PrimaryKeyConstraint,
     Sequence,
@@ -20,6 +21,7 @@
     util,
 )
 from sqlalchemy.engine import Connection, default, reflection
+from sqlalchemy.schema import CreateColumn
 from sqlalchemy.sql import Select, compiler, sqltypes
 from sqlalchemy.sql.ddl import _DropView as BaseDropView
 from sqlalchemy.sql.elements import (
@@ -436,12 +438,25 @@ def visit_drop_view(self, drop: DropView | BaseDropView, **kw: Any) -> str:
             return f"DROP VIEW {self.preparer.format_table(drop.element)}"
         return f"DROP VIEW {drop.name}"
 
+    def visit_create_column(
+        self, create: CreateColumn, first_pk: bool = False, **kw: Any
+    ) -> str:
+        if create.element.autoincrement is True and not create.element.identity:
+            create.element.identity = Identity()
+        return super().visit_create_column(create, first_pk, **kw)
+
 
 class HANAExecutionContext(default.DefaultExecutionContext):
     def fire_sequence(self, seq: Sequence, type_: Integer) -> int:
         seq = self.identifier_preparer.format_sequence(seq)
         return self._execute_scalar(f"SELECT {seq}.NEXTVAL FROM DUMMY", type_)
 
+    def get_lastrowid(self) -> int:
+        self.cursor.execute("SELECT CURRENT_IDENTITY_VALUE () FROM DUMMY")
+        res = self.cursor.fetchone()
+        assert res, "No lastrowid available"
+        return res[0]
+
 
 class HANAInspector(reflection.Inspector):
     dialect: HANAHDBCLIDialect
@@ -475,14 +490,14 @@ class HANAHDBCLIDialect(default.DefaultDialect):
 
     div_is_floordiv = False
     implicit_returning = False
-    postfetch_lastrowid = False
+    postfetch_lastrowid = True
     requires_name_normalize = True
     returns_native_bytes = False
     supports_comments = True
     supports_default_values = False
     supports_empty_insert = False
     supports_for_update_of = True
-    supports_identity_columns = False
+    supports_identity_columns = True
     supports_is_distinct_from = True
     supports_native_boolean = True
     supports_native_decimal = True

test/requirements.py

@@ -55,8 +55,7 @@ def two_phase_transactions(self) -> compound:
 
     @property
     def autoincrement_without_sequence(self) -> compound:
-        # Not supported yet
-        return exclusions.closed()
+        return exclusions.open()
 
     @property
     def isolation_level(self) -> compound:
@@ -302,16 +301,20 @@ def computed_columns_default_persisted(self) -> compound:
     def computed_columns_reflect_persisted(self) -> compound:
         return exclusions.open()
 
-    # identity columns are not supported yet
-
     @property
     def identity_columns(self) -> compound:
-        return exclusions.closed()
+        return exclusions.open()
 
     @property
     def identity_columns_alter(self) -> compound:
+        # SAP HANA does not return the semantics of an identity column
+        # Therefore, no diff can be calculated
         return exclusions.closed()
 
+    @property
+    def identity_columns_standard(self) -> compound:
+        return exclusions.open()
+
     @property
     def autoincrement_insert(self) -> compound:
-        return exclusions.closed()
+        return exclusions.open()

test/test_select.py

@@ -0,0 +1,25 @@
+"""SQL select tests."""
+
+from __future__ import annotations
+
+from sqlalchemy import Integer, String
+from sqlalchemy.testing.assertions import eq_
+from sqlalchemy.testing.fixtures import TablesTest
+from sqlalchemy.testing.schema import Column, Table
+
+
+class SelectTest(TablesTest):
+
+    @classmethod
+    def define_tables(cls, metadata):
+        Table(
+            "tbl",
+            metadata,
+            Column("id", Integer, primary_key=True, autoincrement=True),
+            Column("desc", String(100)),
+        )
+
+    def test_autoincrement(self, connection):
+        res = connection.execute(self.tables.tbl.insert(), {"desc": "row"})
+        res = connection.execute(self.tables.tbl.select()).first()
+        eq_(res, (1, "row"))

test/test_sqlalchemy_dialect_suite.py

@@ -15,7 +15,8 @@
     inspect,
     testing,
 )
-from sqlalchemy.testing.assertions import eq_
+from sqlalchemy.exc import DBAPIError
+from sqlalchemy.testing.assertions import assert_raises, eq_
 from sqlalchemy.testing.provision import temp_table_keyword_args
 from sqlalchemy.testing.schema import Column, Table
 from sqlalchemy.testing.suite import *  # noqa: F401, F403
@@ -26,6 +27,12 @@
 from sqlalchemy.testing.suite.test_reflection import (
     ComponentReflectionTestExtra as _ComponentReflectionTestExtra,
 )
+from sqlalchemy.testing.suite.test_reflection import (
+    IdentityReflectionTest as _IdentityReflectionTest,
+)
+from sqlalchemy.testing.suite.test_select import (
+    IdentityColumnTest as _IdentityColumnTest,
+)
 
 # Import dialect test suite provided by SQLAlchemy into SQLAlchemy-HANA test collection.
 # Please don't add other tests in this file. Only adjust or overview SQLAlchemy tests
@@ -134,3 +141,22 @@ def test_select_recursive_round_trip(self, connection):
 
     def test_insert_from_select_round_trip(self, connection):
         pytest.skip("Insert CTEs are not supported by SAP HANA")
+
+
+class IdentityReflectionTest(_IdentityReflectionTest):
+    def test_reflect_identity(self, connection):
+        pytest.skip("Identity column reflection is not supported")
+
+    def test_reflect_identity_schema(self, connection):
+        pytest.skip("Identity column reflection is not supported")
+
+
+class IdentityColumnTest(_IdentityColumnTest):
+    def test_insert_always_error(self, connection):
+        def fn():
+            connection.execute(
+                self.tables.tbl_a.insert(),
+                [{"id": 200, "desc": "a"}],
+            )
+
+        assert_raises((DBAPIError,), fn)