refactor(catalog): tighten object_type typing and mssql sampleable set

Address review feedback on MR !547:
- Narrow mssql sampleable_object_types to {TABLE} — SQL Server has no materialized
  views, so the MATERIALIZED_VIEW entry never matched.
- Annotate object_type as ObjectType (not str) on ColumnChars and the DataTable
  model/overview, per the StrEnum-everywhere convention.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: aarthy-dk

testgen/common/database/column_chars.py

@@ -20,7 +20,7 @@ class ColumnChars:
     column_type: str | None = None
     db_data_type: str | None = None
     is_decimal: bool = False
-    object_type: str | None = None # ObjectType values
+    object_type: ObjectType | None = None
     approx_record_ct: int | None = None
     # This should not default to 0 since we don't always retrieve actual row counts
     # UI relies on the null value to know that the approx_record_ct should be displayed instead

testgen/common/database/flavor/mssql_flavor_service.py

@@ -11,8 +11,8 @@ class MssqlFlavorService(FlavorService):
     escaped_underscore = "[_]"
     row_limiting_clause = "top"
     url_scheme = "mssql+pyodbc"
-    # TABLESAMPLE applies only to tables and materialized views
-    sampleable_object_types = frozenset({ObjectType.TABLE, ObjectType.MATERIALIZED_VIEW})
+    # TABLESAMPLE is rejected on views; SQL Server has no materialized views, so only base tables.
+    sampleable_object_types = frozenset({ObjectType.TABLE})
 
     def get_connection_string_from_fields(self, params: ResolvedConnectionParams) -> str:
         connection_url = URL.create(

testgen/common/models/data_table.py

@@ -17,6 +17,7 @@
 )
 from sqlalchemy.dialects import postgresql
 
+from testgen.common.database.column_chars import ObjectType
 from testgen.common.models import get_current_session
 from testgen.common.models.data_column import DataColumnChars
 from testgen.common.models.entity import Entity
@@ -42,7 +43,7 @@ class TableProfilingOverview:
     table_groups_id: UUID
     schema_name: str | None
     table_name: str
-    object_type: str | None
+    object_type: ObjectType | None
     record_ct: int | None
     column_ct: int | None
     dq_score_profiling: float | None
@@ -62,7 +63,7 @@ class DataTable(Entity):
     table_groups_id: UUID = Column(postgresql.UUID(as_uuid=True), ForeignKey("table_groups.id"))
     schema_name: str | None = Column(String)
     table_name: str = Column(String)
-    object_type: str | None = Column(String)
+    object_type: ObjectType | None = Column(String)
     column_ct: int | None = Column(BigInteger)
     record_ct: int | None = Column(BigInteger)
     approx_record_ct: int | None = Column(BigInteger)

tests/unit/common/test_flavor_sampling.py

@@ -12,11 +12,15 @@
 pytestmark = pytest.mark.unit
 
 
-@pytest.mark.parametrize("flavor", ["mssql", "postgresql"])
-def test_sampleable_restricted_to_physical_where_clause_rejects_views(flavor):
-    # Verified live: TABLESAMPLE errors on a view for these flavors, so only physical
-    # relations are sampleable; views/external/other are profiled in full.
-    assert get_flavor_service(flavor).sampleable_object_types == {
+# Verified live: TABLESAMPLE errors on a view for these flavors, so only physical relations
+# are sampleable; views/external/other are profiled in full.
+def test_mssql_samples_only_base_tables():
+    # SQL Server has no materialized views, so the sampleable set is just base tables.
+    assert get_flavor_service("mssql").sampleable_object_types == {ObjectType.TABLE}
+
+
+def test_postgresql_samples_tables_and_materialized_views():
+    assert get_flavor_service("postgresql").sampleable_object_types == {
         ObjectType.TABLE,
         ObjectType.MATERIALIZED_VIEW,
     }