fix: skip unnecessary String cast on already-string search columns

src/fastapi_toolsets/crud/search.py

@@ -159,8 +159,11 @@ def build_search_filters(
         else:
             column = field
 
-        # Build the filter (cast to String for non-text columns)
-        column_as_string = column.cast(String)
+        # Build the filter (cast to String only when needed, to preserve
+        # pg_trgm GIN index usability on already-String columns)
+        column_as_string = (
+            column if isinstance(column.type, String) else column.cast(String)
+        )
         if config.case_sensitive:
             filters.append(column_as_string.like(f"%{query}%"))
         else:

tests/test_crud_search.py

@@ -372,6 +372,22 @@ class TestBuildSearchFilters:
 
         assert len(joins) == 1
 
+    def test_skips_cast_on_string_column(self):
+        """String columns are filtered directly, without a CAST (keeps pg_trgm indexable)."""
+        from fastapi_toolsets.crud.search import build_search_filters
+
+        filters, _ = build_search_filters(User, "john", search_fields=[User.username])
+
+        assert "CAST" not in str(filters[0])
+
+    def test_casts_non_string_column(self):
+        """Non-string columns (e.g. UUID) still get cast to String so ilike works."""
+        from fastapi_toolsets.crud.search import build_search_filters
+
+        filters, _ = build_search_filters(User, "123", search_fields=[User.id])
+
+        assert "CAST" in str(filters[0])
+
 
 class TestSearchConfig:
     """Tests for SearchConfig options."""