SQLAlchemy 2: Fix failing mypy checks from development (#257)

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

Author: Jesse

src/databricks/sqlalchemy/_parse.py

@@ -12,6 +12,10 @@
 """
 
 
+class DatabricksSqlAlchemyParseException(Exception):
+    pass
+
+
 def _match_table_not_found_string(message: str) -> bool:
     """Return True if the message contains a substring indicating that a table was not found"""
 
@@ -31,7 +35,7 @@ def _describe_table_extended_result_to_dict_list(
     """Transform the CursorResult of DESCRIBE TABLE EXTENDED into a list of Dictionaries"""
 
     rows_to_return = []
-    for row in result:
+    for row in result.all():
         this_row = {"col_name": row.col_name, "data_type": row.data_type}
         rows_to_return.append(this_row)
 
@@ -69,24 +73,33 @@ def extract_three_level_identifier_from_constraint_string(input_str: str) -> dic
             "schema": "pysql_dialect_compliance",
             "table": "users"
         }
+
+    Raise a DatabricksSqlAlchemyParseException if a 3L namespace isn't found
     """
     pat = re.compile(r"REFERENCES\s+(.*?)\s*\(")
     matches = pat.findall(input_str)
 
     if not matches:
-        return None
+        raise DatabricksSqlAlchemyParseException(
+            "3L namespace not found in constraint string"
+        )
 
     first_match = matches[0]
     parts = first_match.split(".")
 
     def strip_backticks(input: str):
         return input.replace("`", "")
 
-    return {
-        "catalog": strip_backticks(parts[0]),
-        "schema": strip_backticks(parts[1]),
-        "table": strip_backticks(parts[2]),
-    }
+    try:
+        return {
+            "catalog": strip_backticks(parts[0]),
+            "schema": strip_backticks(parts[1]),
+            "table": strip_backticks(parts[2]),
+        }
+    except IndexError:
+        raise DatabricksSqlAlchemyParseException(
+            "Incomplete 3L namespace found in constraint string: " + ".".join(parts)
+        )
 
 
 def _parse_fk_from_constraint_string(constraint_str: str) -> dict:
@@ -170,10 +183,12 @@ def build_fk_dict(
     else:
         schema_override_dict = {}
 
+    # mypy doesn't like this method of conditionally adding a key to a dictionary
+    # while keeping everything immutable
     complete_foreign_key_dict = {
         "name": fk_name,
         **base_fk_dict,
-        **schema_override_dict,
+        **schema_override_dict,  # type: ignore
     }
 
     return complete_foreign_key_dict
@@ -234,7 +249,7 @@ def match_dte_rows_by_value(dte_output: List[Dict[str, str]], match: str) -> Lis
     return output_rows
 
 
-def get_fk_strings_from_dte_output(dte_output: List[List]) -> List[dict]:
+def get_fk_strings_from_dte_output(dte_output: List[Dict[str, str]]) -> List[dict]:
     """If the DESCRIBE TABLE EXTENDED output contains foreign key constraints, return a list of dictionaries,
     one dictionary per defined constraint
     """
@@ -307,7 +322,11 @@ def parse_column_info_from_tgetcolumnsresponse(thrift_resp_row) -> ReflectedColu
     """
 
     pat = re.compile(r"^\w+")
-    _raw_col_type = re.search(pat, thrift_resp_row.TYPE_NAME).group(0).lower()
+
+    # This method assumes a valid TYPE_NAME field in the response.
+    # TODO: add error handling in case TGetColumnsResponse format changes
+
+    _raw_col_type = re.search(pat, thrift_resp_row.TYPE_NAME).group(0).lower()  # type: ignore
     _col_type = GET_COLUMNS_TYPE_MAP[_raw_col_type]
 
     if _raw_col_type == "decimal":
@@ -334,4 +353,5 @@ def parse_column_info_from_tgetcolumnsresponse(thrift_resp_row) -> ReflectedColu
         "default": thrift_resp_row.COLUMN_DEF,
     }
 
-    return this_column
+    # TODO: figure out how to return sqlalchemy.interfaces in a way that mypy respects
+    return this_column  # type: ignore

src/databricks/sqlalchemy/base.py

@@ -1,5 +1,5 @@
 import re
-from typing import Any, List, Optional, Dict, Collection, Iterable, Tuple
+from typing import Any, List, Optional, Dict, Union, Collection, Iterable, Tuple
 
 import databricks.sqlalchemy._ddl as dialect_ddl_impl
 import databricks.sqlalchemy._types as dialect_type_impl
@@ -73,10 +73,12 @@ class DatabricksDialect(default.DefaultDialect):
 
     # SQLAlchemy requires that a table with no primary key
     # constraint return a dictionary that looks like this.
-    EMPTY_PK = {"constrained_columns": [], "name": None}
+    EMPTY_PK: Dict[str, Any] = {"constrained_columns": [], "name": None}
 
     # SQLAlchemy requires that a table with no foreign keys
     # defined return an empty list. Same for indexes.
+    EMPTY_FK: List
+    EMPTY_INDEX: List
     EMPTY_FK = EMPTY_INDEX = []
 
     @classmethod
@@ -139,7 +141,7 @@ def _describe_table_extended(
         catalog_name: Optional[str] = None,
         schema_name: Optional[str] = None,
         expect_result=True,
-    ) -> List[Dict[str, str]]:
+    ) -> Union[List[Dict[str, str]], None]:
         """Run DESCRIBE TABLE EXTENDED on a table and return a list of dictionaries of the result.
 
         This method is the fastest way to check for the presence of a table in a schema.
@@ -158,7 +160,7 @@ def _describe_table_extended(
         stmt = DDL(f"DESCRIBE TABLE EXTENDED {_target}")
 
         try:
-            result = connection.execute(stmt).all()
+            result = connection.execute(stmt)
         except DatabaseError as e:
             if _match_table_not_found_string(str(e)):
                 raise sqlalchemy.exc.NoSuchTableError(
@@ -197,9 +199,11 @@ def get_pk_constraint(
             schema_name=schema,
         )
 
-        raw_pk_constraints: List = get_pk_strings_from_dte_output(result)
+        # Type ignore is because mypy knows that self._describe_table_extended *can*
+        # return None (even though it never will since expect_result defaults to True)
+        raw_pk_constraints: List = get_pk_strings_from_dte_output(result)  # type: ignore
         if not any(raw_pk_constraints):
-            return self.EMPTY_PK
+            return self.EMPTY_PK  # type: ignore
 
         if len(raw_pk_constraints) > 1:
             logger.warning(
@@ -212,11 +216,12 @@ def get_pk_constraint(
         pk_name = first_pk_constraint.get("col_name")
         pk_constraint_string = first_pk_constraint.get("data_type")
 
-        return build_pk_dict(pk_name, pk_constraint_string)
+        # TODO: figure out how to return sqlalchemy.interfaces in a way that mypy respects
+        return build_pk_dict(pk_name, pk_constraint_string)  # type: ignore
 
     def get_foreign_keys(
         self, connection, table_name, schema=None, **kw
-    ) -> ReflectedForeignKeyConstraint:
+    ) -> List[ReflectedForeignKeyConstraint]:
         """Return information about foreign_keys in `table_name`."""
 
         result = self._describe_table_extended(
@@ -225,7 +230,9 @@ def get_foreign_keys(
             schema_name=schema,
         )
 
-        raw_fk_constraints: List = get_fk_strings_from_dte_output(result)
+        # Type ignore is because mypy knows that self._describe_table_extended *can*
+        # return None (even though it never will since expect_result defaults to True)
+        raw_fk_constraints: List = get_fk_strings_from_dte_output(result)  # type: ignore
 
         if not any(raw_fk_constraints):
             return self.EMPTY_FK
@@ -239,7 +246,8 @@ def get_foreign_keys(
             )
             fk_constraints.append(this_constraint_dict)
 
-        return fk_constraints
+        # TODO: figure out how to return sqlalchemy.interfaces in a way that mypy respects
+        return fk_constraints  # type: ignore
 
     def get_indexes(self, connection, table_name, schema=None, **kw):
         """SQLAlchemy requires this method. Databricks doesn't support indexes."""

src/databricks/sqlalchemy/test/_future.py

@@ -1,3 +1,5 @@
+# type: ignore
+
 from enum import Enum
 
 import pytest

src/databricks/sqlalchemy/test/_regression.py

@@ -1,3 +1,5 @@
+# type: ignore
+
 import pytest
 from sqlalchemy.testing.suite import (
     ArgSignatureTest,

src/databricks/sqlalchemy/test/_unsupported.py

@@ -1,3 +1,5 @@
+# type: ignore
+
 from enum import Enum
 
 import pytest

src/databricks/sqlalchemy/test_local/test_parsing.py

@@ -6,6 +6,7 @@
     build_fk_dict,
     build_pk_dict,
     match_dte_rows_by_value,
+    DatabricksSqlAlchemyParseException,
 )
 
 
@@ -55,6 +56,13 @@ def test_extract_3l_namespace_from_constraint_string():
     ), "Failed to extract 3L namespace from constraint string"
 
 
+def test_extract_3l_namespace_from_bad_constraint_string():
+    input = "FOREIGN KEY (`parent_user_id`) REFERENCES `pysql_dialect_compliance`.`users` (`user_id`)"
+
+    with pytest.raises(DatabricksSqlAlchemyParseException):
+        extract_three_level_identifier_from_constraint_string(input)
+
+
 @pytest.mark.parametrize("schema", [None, "some_schema"])
 def test_build_fk_dict(schema):
     fk_constraint_string = "FOREIGN KEY (`parent_user_id`) REFERENCES `main`.`some_schema`.`users` (`user_id`)"