Add support for save_table(..., mode="overwrite") to StatementExecutionBackend

src/databricks/labs/lsql/backends.py

@@ -146,15 +146,14 @@ def fetch(self, sql: str) -> Iterator[Row]:
         return self._sql.fetch_all(sql)
 
     def save_table(self, full_name: str, rows: Sequence[DataclassInstance], klass: Dataclass, mode="append"):
-        if mode == "overwrite":
-            msg = "Overwrite mode is not yet supported"
-            raise NotImplementedError(msg)
         rows = self._filter_none_rows(rows, klass)
         self.create_table(full_name, klass)
         if len(rows) == 0:
             return
         fields = dataclasses.fields(klass)
         field_names = [f.name for f in fields]
+        if mode == "overwrite":
+            self.execute(f"TRUNCATE TABLE {full_name}")
         for i in range(0, len(rows), self._max_records_per_batch):
             batch = rows[i : i + self._max_records_per_batch]
             vals = "), (".join(self._row_to_sql(r, fields) for r in batch)
@@ -283,10 +282,9 @@ def fetch(self, sql) -> Iterator[Row]:
         return iter(rows)
 
     def save_table(self, full_name: str, rows: Sequence[DataclassInstance], klass: Dataclass, mode: str = "append"):
-        if mode == "overwrite":
-            msg = "Overwrite mode is not yet supported"
-            raise NotImplementedError(msg)
         rows = self._filter_none_rows(rows, klass)
+        if mode == "overwrite":
+            self._save_table = []
         if klass.__class__ == type:
             row_factory = self._row_factory(klass)
             rows = [row_factory(*dataclasses.astuple(r)) for r in rows]

tests/integration/test_deployment.py

@@ -22,3 +22,14 @@ def test_deploys_database(ws, env_or_skip, make_random):
     rows = list(sql_backend.fetch(f"SELECT * FROM {schema}.some"))
 
     assert rows == [Row(name="abc", id=1)]
+
+
+def test_overwrite(ws, env_or_skip, make_random):
+    schema = "default"
+    sql_backend = StatementExecutionBackend(ws, env_or_skip("TEST_DEFAULT_WAREHOUSE_ID"))
+
+    sql_backend.save_table(f"{schema}.foo", [views.Foo("abc", True)], views.Foo, "append")
+    sql_backend.save_table(f"{schema}.foo", [views.Foo("xyz", True)], views.Foo, "overwrite")
+    rows = list(sql_backend.fetch(f"SELECT * FROM {schema}.some"))
+
+    assert rows == [Row(name="xyz", id=1)]

tests/unit/test_backends.py

@@ -93,10 +93,47 @@ def test_statement_execution_backend_fetch_happy():
     assert [Row(id=1), Row(id=2), Row(id=3)] == result
 
 
-def test_statement_execution_backend_save_table_overwrite(mocker):
-    seb = StatementExecutionBackend(mocker.Mock(), "abc")
-    with pytest.raises(NotImplementedError):
-        seb.save_table("a.b.c", [1, 2, 3], Bar, mode="overwrite")
+def test_statement_execution_backend_save_table_overwrite_empty_table():
+    ws = create_autospec(WorkspaceClient)
+    ws.statement_execution.execute_statement.return_value = ExecuteStatementResponse(
+        status=StatementStatus(state=StatementState.SUCCEEDED)
+    )
+    seb = StatementExecutionBackend(ws, "abc")
+    seb.save_table("a.b.c", [Baz("1")], Baz, mode="overwrite")
+    ws.statement_execution.execute_statement.assert_has_calls(
+        [
+            mock.call(
+                warehouse_id="abc",
+                statement="CREATE TABLE IF NOT EXISTS a.b.c (first STRING NOT NULL, second STRING) USING DELTA",
+                catalog=None,
+                schema=None,
+                disposition=None,
+                format=Format.JSON_ARRAY,
+                byte_limit=None,
+                wait_timeout=None,
+            ),
+            mock.call(
+                warehouse_id="abc",
+                statement="TRUNCATE TABLE a.b.c",
+                catalog=None,
+                schema=None,
+                disposition=None,
+                format=Format.JSON_ARRAY,
+                byte_limit=None,
+                wait_timeout=None,
+            ),
+            mock.call(
+                warehouse_id="abc",
+                statement="INSERT INTO a.b.c (first, second) VALUES ('1', NULL)",
+                catalog=None,
+                schema=None,
+                disposition=None,
+                format=Format.JSON_ARRAY,
+                byte_limit=None,
+                wait_timeout=None,
+            ),
+        ]
+    )
 
 
 def test_statement_execution_backend_save_table_empty_records():
@@ -357,3 +394,16 @@ def test_mock_backend_rows_dsl():
         Row(foo=1, bar=2),
         Row(foo=3, bar=4),
     ]
+
+
+def test_mock_backend_overwrite():
+    mock_backend = MockBackend()
+    mock_backend.save_table("a.b.c", [Foo("a1", True), Foo("c2", False)], Foo, "append")
+    mock_backend.save_table("a.b.c", [Foo("aa", True), Foo("bb", False)], Foo, "overwrite")
+    mock_backend.save_table("a.b.c", [Foo("aaa", True), Foo("bbb", False)], Foo, "overwrite")
+
+    assert mock_backend.rows_written_for("a.b.c", "append") == []
+    assert mock_backend.rows_written_for("a.b.c", "overwrite") == [
+        Row(first="aaa", second=True),
+        Row(first="bbb", second=False),
+    ]