SQLAlchemy: fix has_table so it honours schema= argument (databricks#174

)

---------
Signed-off-by: Jesse Whitehouse <jesse.whitehouse@databricks.com>

CHANGELOG.md

@@ -3,10 +3,12 @@
 ## 2.7.x (Unreleased)
 
 - Add support for Cloud Fetch (#146, #151, #154)
+- SQLAlchemy has_table function now honours schema= argument and adds catalog= argument (#174)
 - Fix: Revised SQLAlchemy dialect and examples for compatibility with SQLAlchemy==1.3.x (#173)
 - Fix: oauth would fail if expired credentials appeared in ~/.netrc (#122)
 - Fix: Python HTTP proxies were broken after switch to urllib3 (#158)
 - Other: Connector now logs operation handle guids as hexadecimal instead of bytes (#170)
+- Add support for Cloud Fetch
 
 ## 2.7.0 (2023-06-26)
 

src/databricks/sqlalchemy/dialect/__init__.py

@@ -267,17 +267,22 @@ def do_rollback(self, dbapi_connection):
         # Databricks SQL Does not support transactions
         pass
 
-    def has_table(self, connection, table_name, schema=None, **kwargs) -> bool:
+    def has_table(
+        self, connection, table_name, schema=None, catalog=None, **kwargs
+    ) -> bool:
         """SQLAlchemy docstrings say dialect providers must implement this method"""
 
-        schema = schema or "default"
+        _schema = schema or self.schema
+        _catalog = catalog or self.catalog
 
         # DBR >12.x uses underscores in error messages
         DBR_LTE_12_NOT_FOUND_STRING = "Table or view not found"
         DBR_GT_12_NOT_FOUND_STRING = "TABLE_OR_VIEW_NOT_FOUND"
 
         try:
-            res = connection.execute(f"DESCRIBE TABLE {table_name}")
+            res = connection.execute(
+                f"DESCRIBE TABLE {_catalog}.{_schema}.{table_name}"
+            )
             return True
         except DatabaseError as e:
             if DBR_GT_12_NOT_FOUND_STRING in str(

tests/e2e/sqlalchemy/test_basic.py

@@ -340,3 +340,44 @@ def test_get_table_names_smoke_test(samples_engine: Engine):
     with samples_engine.connect() as conn:
         _names = samples_engine.table_names(schema="nyctaxi", connection=conn)
         _names is not None, "get_table_names did not succeed"
+
+
+def test_has_table_across_schemas(db_engine: Engine, samples_engine: Engine):
+    """For this test to pass these conditions must be met:
+        - Table samples.nyctaxi.trips must exist
+        - Table samples.tpch.customer must exist
+        - The `catalog` and `schema` environment variables must be set and valid
+    """
+
+    with samples_engine.connect() as conn:
+
+        # 1) Check for table within schema declared at engine creation time
+        assert samples_engine.dialect.has_table(connection=conn, table_name="trips")
+
+        # 2) Check for table within another schema in the same catalog
+        assert samples_engine.dialect.has_table(
+            connection=conn, table_name="customer", schema="tpch"
+        )
+
+        # 3) Check for a table within a different catalog
+        other_catalog = os.environ.get("catalog")
+        other_schema = os.environ.get("schema")
+
+        # Create a table in a different catalog
+        with db_engine.connect() as conn:
+            conn.execute("CREATE TABLE test_has_table (numbers_are_cool INT);")
+
+            try:
+                # Verify that this table is not found in the samples catalog
+                assert not samples_engine.dialect.has_table(
+                    connection=conn, table_name="test_has_table"
+                )
+                # Verify that this table is found in a separate catalog
+                assert samples_engine.dialect.has_table(
+                    connection=conn,
+                    table_name="test_has_table",
+                    schema=other_schema,
+                    catalog=other_catalog,
+                )
+            finally:
+                conn.execute("DROP TABLE test_has_table;")