fix(migrations): eliminate duplicate SQL file loading

sqlspec/migrations/loaders.py

@@ -93,7 +93,6 @@ async def get_up_sql(self, path: Path) -> list[str]:
         Raises:
             MigrationLoadError: If migration file is invalid or missing up query.
         """
-        self.sql_loader.clear_cache()
         self.sql_loader.load_sql(path)
 
         version = self._extract_version(path.name)
@@ -115,7 +114,6 @@ async def get_down_sql(self, path: Path) -> list[str]:
         Returns:
             List containing single SQL statement for downgrade, or empty list.
         """
-        self.sql_loader.clear_cache()
         self.sql_loader.load_sql(path)
 
         version = self._extract_version(path.name)
@@ -141,7 +139,6 @@ def validate_migration_file(self, path: Path) -> None:
             msg = f"Invalid migration filename: {path.name}"
             raise MigrationLoadError(msg)
 
-        self.sql_loader.clear_cache()
         self.sql_loader.load_sql(path)
         up_query = f"migrate-{version}-up"
         if not self.sql_loader.has_query(up_query):

sqlspec/migrations/runner.py

@@ -228,7 +228,6 @@ def load_migration(self, file_path: Path, version: "str | None" = None) -> "dict
         if file_path.suffix == ".sql":
             version = metadata["version"]
             up_query, down_query = f"migrate-{version}-up", f"migrate-{version}-down"
-            self.loader.clear_cache()
             self.loader.load_sql(file_path)
             has_upgrade, has_downgrade = self.loader.has_query(up_query), self.loader.has_query(down_query)
         else:
@@ -394,7 +393,6 @@ async def load_migration(self, file_path: Path, version: "str | None" = None) ->
         if file_path.suffix == ".sql":
             version = metadata["version"]
             up_query, down_query = f"migrate-{version}-up", f"migrate-{version}-down"
-            self.loader.clear_cache()
             await async_(self.loader.load_sql)(file_path)
             has_upgrade, has_downgrade = self.loader.has_query(up_query), self.loader.has_query(down_query)
         else:

tests/unit/test_migrations/test_migration_runner.py

@@ -538,3 +538,41 @@ def test_many_migration_files_performance() -> None:
         for i, (version, _) in enumerate(files):
             expected_version = f"{i + 1:04d}"
             assert version == expected_version
+
+
+def test_sql_loader_caches_files() -> None:
+    """Test that SQL migration files leverage CoreSQLFileLoader caching.
+
+    Verifies fix for bug #118 - duplicate SQL loading during migrations.
+    The SQLFileLoader should NOT call clear_cache() before operations,
+    allowing CoreSQLFileLoader's internal caching to work properly.
+    """
+    import asyncio
+
+    from sqlspec.migrations.loaders import SQLFileLoader
+
+    with tempfile.TemporaryDirectory() as temp_dir:
+        migrations_path = Path(temp_dir)
+
+        migration_file = migrations_path / "0001_test_migration.sql"
+        migration_content = """
+-- name: migrate-0001-up
+CREATE TABLE test (id INTEGER PRIMARY KEY);
+
+-- name: migrate-0001-down
+DROP TABLE test;
+"""
+        migration_file.write_text(migration_content)
+
+        sql_loader = SQLFileLoader()
+
+        async def test_operations() -> None:
+            await sql_loader.get_up_sql(migration_file)
+            path_str = str(migration_file)
+            assert path_str in sql_loader.sql_loader._files
+            assert sql_loader.sql_loader.has_query("migrate-0001-up")
+            assert sql_loader.sql_loader.has_query("migrate-0001-down")
+            await sql_loader.get_down_sql(migration_file)
+            assert path_str in sql_loader.sql_loader._files
+
+        asyncio.run(test_operations())