Preserve metadata when merging cubes without bands

CHANGELOG.md

@@ -22,7 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Better error message when passing a bounding box with field typos in `Connection.load_collection()` and alike  ([#910](https://github.com/Open-EO/openeo-python-client/issues/910))
-
+- Preserve available band metadata when merging data cubes if one cube has no band dimension. ([#783](https://github.com/Open-EO/openeo-python-client/issues/783))
 
 ## [0.50.0] - 2026-05-18
 

openeo/rest/datacube.py

@@ -2183,18 +2183,16 @@ def merge_cubes(
         arguments = {"cube1": self, "cube2": other}
         if overlap_resolver:
             arguments["overlap_resolver"] = build_child_callback(overlap_resolver, parent_parameters=["x", "y"])
-        if (
-            self.metadata
-            and self.metadata.has_band_dimension()
-            and isinstance(other, DataCube)
-            and other.metadata
-            and other.metadata.has_band_dimension()
-        ):
-            # Minimal client side metadata merging
+        if self.metadata and isinstance(other, DataCube) and other.metadata:
+            # Minimal client-side metadata merging: preserve metadata when one or
+            # both cubes have no band dimension, and merge bands when both do.
             merged_metadata = self.metadata
-            for b in other.metadata.band_dimension.bands:
-                if b not in merged_metadata.bands:
-                    merged_metadata = merged_metadata.append_band(b)
+            if self.metadata.has_band_dimension() and other.metadata.has_band_dimension():
+                for b in other.metadata.band_dimension.bands:
+                    if b not in merged_metadata.bands:
+                        merged_metadata = merged_metadata.append_band(b)
+            elif other.metadata.has_band_dimension():
+                merged_metadata = other.metadata
         else:
             merged_metadata = None
         # Overlapping bands without overlap resolver will give an error in the backend

tests/rest/datacube/test_datacube100.py

@@ -1185,6 +1185,32 @@ def test_merge_cubes_band_merging_with_overlap(con100, requests_mock, overlap_re
     assert s4_f_m_s3_f.metadata.band_names == ["B6", "B5", "B8"]
 
 
+def test_merge_cubes_band_metadata_one_sided(con100):
+    bands = con100.load_collection("S2")
+    no_bands = bands.ndvi()
+
+    assert bands.metadata.has_band_dimension()
+    assert not no_bands.metadata.has_band_dimension()
+    assert bands.merge_cubes(no_bands).metadata.band_names == ["B02", "B03", "B04", "B08"]
+    assert no_bands.merge_cubes(bands).metadata.band_names == ["B02", "B03", "B04", "B08"]
+
+
+def test_merge_cubes_metadata_without_band_dimensions(con100):
+    no_bands = con100.load_collection("S2").ndvi()
+    merged = no_bands.merge_cubes(no_bands)
+
+    assert merged.metadata is no_bands.metadata
+    assert not merged.metadata.has_band_dimension()
+
+
+def test_merge_cubes_missing_metadata(con100):
+    with_metadata = con100.load_collection("S2")
+    without_metadata = con100.load_collection("S2", fetch_metadata=False)
+
+    assert with_metadata.merge_cubes(without_metadata).metadata is None
+    assert without_metadata.merge_cubes(with_metadata).metadata is None
+
+
 def test_resample_cube_spatial(con100: Connection):
     data = con100.load_collection("S2")
     target = con100.load_collection("MASK")