fix: refresh materialized_view when databricks_tags is set (#1419)

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Fix DBR capability cache being permanently poisoned by a transient version-query failure ([#1398](https://github.com/databricks/dbt-databricks/issues/1398))
 - Fix spurious `use_managed_iceberg` behavior-change warning firing on every run for projects that don't use Iceberg ([#1266](https://github.com/databricks/dbt-databricks/issues/1266))
 - Warn when `contract.enforced: true` is set on a `materialized_view` model ([#1279](https://github.com/databricks/dbt-databricks/issues/1279))
+- Fix `materialized_view` models with `databricks_tags` silently going stale on `dbt run`. `MaterializedViewAPI._describe_relation` was not fetching `information_schema.tags`, so existing tags always parsed as empty, producing a spurious tag diff that routed the materialization to `ALTER ... SET TAGS` instead of `REFRESH MATERIALIZED VIEW` ([#1419](https://github.com/databricks/dbt-databricks/issues/1419))
 
 ## dbt-databricks 1.11.7 (Apr 17, 2026)
 

dbt/adapters/databricks/impl.py

@@ -1091,6 +1091,7 @@ def _describe_relation(
         results["information_schema.views"] = get_first_row(
             adapter.execute_macro("get_view_description", kwargs=kwargs)
         )
+        results["information_schema.tags"] = adapter.execute_macro("fetch_tags", kwargs=kwargs)
         results["show_tblproperties"] = adapter.execute_macro("fetch_tbl_properties", kwargs=kwargs)
         return results
 

tests/functional/adapter/materialized_view_tests/test_refresh_with_tags.py

@@ -0,0 +1,65 @@
+import pytest
+from dbt.adapters.base import BaseRelation
+from dbt.tests import util
+
+from dbt.adapters.databricks.relation import DatabricksRelationType
+
+SEED_CSV = """id,value
+1,100
+2,200
+""".lstrip()
+
+MV_WITH_TAGS = """
+{{ config(
+    materialized='materialized_view',
+    on_configuration_change='apply',
+    databricks_tags={'deployment': 'DBT'},
+) }}
+select * from {{ ref('mv_seed') }}
+"""
+
+
+@pytest.mark.dlt
+@pytest.mark.skip_profile("databricks_cluster", "databricks_uc_cluster")
+class TestMaterializedViewRefreshesWithTags:
+    @pytest.fixture(scope="class")
+    def seeds(self):
+        return {"mv_seed.csv": SEED_CSV}
+
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {"mv_with_tags.sql": MV_WITH_TAGS}
+
+    @staticmethod
+    def _row_count(project, relation: BaseRelation) -> int:
+        return project.run_sql(f"select count(*) from {relation}", fetch="one")[0]
+
+    def test_mv_refreshes_on_rerun_when_tags_set(self, project):
+        util.run_dbt(["seed"])
+        util.run_dbt(["run", "--models", "mv_with_tags"])
+
+        mv = project.adapter.Relation.create(
+            identifier="mv_with_tags",
+            schema=project.test_schema,
+            database=project.database,
+            type=DatabricksRelationType.MaterializedView,
+        )
+        seed = project.adapter.Relation.create(
+            identifier="mv_seed",
+            schema=project.test_schema,
+            database=project.database,
+        )
+
+        assert self._row_count(project, mv) == 2
+
+        project.run_sql(f"insert into {seed} values (3, 300)")
+        assert self._row_count(project, mv) == 2
+
+        util.run_dbt(["run", "--models", "mv_with_tags"])
+
+        # get_relation_config goes through DeltaLiveTableAPIBase.get_from_relation,
+        # which polls the DLT pipeline until any in-flight refresh completes.
+        with util.get_connection(project.adapter):
+            project.adapter.get_relation_config(mv)
+
+        assert self._row_count(project, mv) == 3, "MV not refreshed on rerun."

tests/unit/relation_configs/test_materialized_view_config.py

@@ -1,7 +1,8 @@
-from unittest.mock import Mock
+from unittest.mock import MagicMock, Mock
 
 from agate import Row, Table
 
+from dbt.adapters.databricks.impl import MaterializedViewAPI
 from dbt.adapters.databricks.relation_configs.comment import CommentConfig
 from dbt.adapters.databricks.relation_configs.liquid_clustering import LiquidClusteringConfig
 from dbt.adapters.databricks.relation_configs.materialized_view import (
@@ -144,3 +145,17 @@ def test_get_changeset__some_changes(self):
             "refresh": RefreshConfig(cron="*/5 * * * *"),
             "tags": TagsConfig(set_tags={"a": "b", "c": "d"}),
         }
+
+
+class TestMaterializedViewAPIDescribeRelation:
+    def test_describe_relation_fetches_tags(self):
+        # Without fetching tags here, an MV with `databricks_tags` would show a
+        # spurious tag diff on every run, routing to ALTER instead of REFRESH.
+        adapter = MagicMock()
+        adapter.execute_macro.return_value = MagicMock()
+
+        results = MaterializedViewAPI._describe_relation(adapter, MagicMock())
+
+        assert "information_schema.tags" in results
+        macro_names = {call.args[0] for call in adapter.execute_macro.call_args_list}
+        assert "fetch_tags" in macro_names