Raise error when transform yields no files

servicex/dataset_identifier.py

@@ -56,6 +56,11 @@ def hash(self):
         sha = hashlib.sha256(str([self.dataset]).encode("utf-8"))
         return sha.hexdigest()
 
+    def describe(self) -> str:
+        """Return a human readable description of this dataset."""
+
+        return self.did
+
 
 class RucioDatasetIdentifier(DataSetIdentifier):
     def __init__(self, dataset: str, num_files: Optional[int] = None):
@@ -107,6 +112,17 @@ def populate_transform_request(self, transform_request: TransformRequest) -> Non
     def did(self):
         return None
 
+    def describe(self) -> str:
+        """Return a human readable description of the configured file list."""
+
+        file_count: int = len(self.files)
+        file_word: str = "file" if file_count == 1 else "files"
+        preview_count: int = min(3, file_count)
+        preview: str = ", ".join(self.files[:preview_count])
+        suffix: str = ", ..." if file_count > preview_count else ""
+
+        return f"{file_count} {file_word}: {preview}{suffix}"
+
     yaml_tag = "!FileList"
 
     @classmethod

servicex/query_core.py

@@ -131,6 +131,11 @@ def generate_selection_string(self) -> str:
             raise RuntimeError("query string generator not set")
         return self.query_string_generator.generate_selection_string()
 
+    def _describe_dataset(self) -> str:
+        """Return a human-readable description of the dataset for error messages."""
+
+        return self.dataset_identifier.describe()
+
     @property
     def transform_request(self):
         if not self.result_format:
@@ -355,6 +360,17 @@ def transform_complete(task: Task):
             downloaded_files = []
 
             download_result = await download_files_task
+            if (
+                not download_result
+                and self.current_status
+                and self.current_status.status == Status.complete
+                and self.current_status.files_completed == 0
+                and self.current_status.files_failed == 0
+            ):
+                dataset_description = self._describe_dataset()
+                raise ServiceXException(
+                    f"Dataset {dataset_description} does not exist or has zero files."
+                )
             if signed_urls_only:
                 signed_urls = download_result
                 if cached_record:

tests/test_dataset.py

@@ -31,7 +31,7 @@
 import datetime
 
 from unittest.mock import AsyncMock, Mock, patch
-from servicex.dataset_identifier import FileListDataset
+from servicex.dataset_identifier import FileListDataset, RucioDatasetIdentifier
 from servicex.configuration import Configuration
 from servicex.minio_adapter import MinioAdapter
 from servicex.query_core import Query
@@ -320,7 +320,7 @@ async def test_submit_and_download_cache_miss(python_dataset, completed_status):
         python_dataset.servicex.get_transform_status.return_value = completed_status
         python_dataset.servicex.submit_transform = AsyncMock()
         python_dataset.download_files = AsyncMock()
-        python_dataset.download_files.return_value = []
+        python_dataset.download_files.return_value = ["1.parquet"]
         python_dataset.cache.update_transform_request_id = Mock()
 
         signed_urls_only = False
@@ -353,7 +353,7 @@ async def test_submit_and_download_cache_miss_overall_progress(
         python_dataset.servicex.get_transform_status.return_value = completed_status
         python_dataset.servicex.submit_transform = AsyncMock()
         python_dataset.download_files = AsyncMock()
-        python_dataset.download_files.return_value = []
+        python_dataset.download_files.return_value = ["1.parquet"]
         python_dataset.cache.update_transform_request_id = Mock()
 
         signed_urls_only = False
@@ -390,7 +390,7 @@ async def test_submit_and_download_no_result_format(python_dataset, completed_st
             python_dataset.servicex.get_transform_status.return_value = completed_status
             python_dataset.servicex.submit_transform = AsyncMock()
             python_dataset.download_files = AsyncMock()
-            python_dataset.download_files.return_value = []
+            python_dataset.download_files.return_value = ["1.parquet"]
             signed_urls_only = False
             expandable_progress = ExpandableProgress()
             await python_dataset.submit_and_download(
@@ -422,7 +422,7 @@ async def test_submit_and_download_cache_miss_signed_urls_only(
         python_dataset.servicex.get_transform_status.return_value = completed_status
         python_dataset.servicex.submit_transform = AsyncMock()
         python_dataset.download_files = AsyncMock()
-        python_dataset.download_files.return_value = []
+        python_dataset.download_files.return_value = ["signed://url"]
         python_dataset.cache.update_transform_request_id = Mock()
 
         signed_urls_only = True
@@ -436,6 +436,48 @@ async def test_submit_and_download_cache_miss_signed_urls_only(
         cache.close()
 
 
+@pytest.mark.asyncio
+async def test_submit_and_download_raises_for_empty_results(
+    python_dataset, completed_status
+):
+    with tempfile.TemporaryDirectory() as temp_dir:
+        python_dataset.dataset_identifier = RucioDatasetIdentifier(
+            "scope:missing_dataset"
+        )
+        python_dataset.current_status = None
+        python_dataset.servicex = AsyncMock()
+        config = Configuration(cache_path=temp_dir, api_endpoints=[])
+        cache = QueryCache(config)
+        python_dataset.cache = cache
+        python_dataset.configuration = config
+        python_dataset.cache.get_transform_by_hash = Mock(return_value=None)
+        python_dataset.servicex.get_transform_status = AsyncMock(id="12345")
+        complete_status = completed_status.model_copy(deep=True)
+        complete_status.status = Status.complete
+        complete_status.files = 0
+        complete_status.files_completed = 0
+        complete_status.files_failed = 0
+        python_dataset.servicex.get_transform_status.return_value = complete_status
+        python_dataset.servicex.submit_transform = AsyncMock()
+        python_dataset.download_files = AsyncMock(return_value=[])
+        python_dataset.cache.update_transform_request_id = Mock()
+
+        signed_urls_only = False
+        expandable_progress = ExpandableProgress()
+
+        with pytest.raises(
+            ServiceXException,
+            match=(
+                r"Dataset rucio://scope:missing_dataset "
+                r"does not exist or has zero files."
+            ),
+        ):
+            await python_dataset.submit_and_download(
+                signed_urls_only, expandable_progress
+            )
+        cache.close()
+
+
 @pytest.mark.asyncio
 async def test_submit_and_download_cache_files_request_urls(
     python_dataset, transformed_result
@@ -525,7 +567,7 @@ async def test_network_loss(python_dataset, transformed_result):
         python_dataset.servicex.get_transform_status.return_value = status
         python_dataset.servicex.submit_transform = AsyncMock()
         python_dataset.download_files = AsyncMock()
-        python_dataset.download_files.return_value = []
+        python_dataset.download_files.return_value = ["1.parquet"]
 
         signed_urls_only = False
         expandable_progress = ExpandableProgress()
@@ -556,7 +598,7 @@ async def test_submit_and_download_get_request_id_from_previous_submitted_reques
         python_dataset.servicex.get_transform_status.return_value = completed_status
         python_dataset.servicex.submit_transform = AsyncMock()
         python_dataset.download_files = AsyncMock()
-        python_dataset.download_files.return_value = []
+        python_dataset.download_files.return_value = ["signed://url"]
         python_dataset.cache.is_transform_request_submitted = Mock(return_value=True)
         python_dataset.cache.get_transform_request_id = Mock(
             return_value="b8c508d0-ccf2-4deb-a1f7-65c839eebabf"

tests/test_dataset_identifier.py

@@ -26,9 +26,11 @@
 # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 from servicex.dataset_identifier import (
+    CERNOpenDataDatasetIdentifier,
     DataSetIdentifier,
-    RucioDatasetIdentifier,
     FileListDataset,
+    RucioDatasetIdentifier,
+    XRootDDatasetIdentifier,
 )
 import pytest
 
@@ -41,6 +43,12 @@ def test_did():
 def test_rucio():
     did = RucioDatasetIdentifier("abc:123-456")
     assert did.did == "rucio://abc:123-456"
+    assert did.describe() == "rucio://abc:123-456"
+
+
+def test_rucio_with_file_limit():
+    did = RucioDatasetIdentifier("abc:123-456", num_files=10)
+    assert did.describe() == "rucio://abc:123-456?files=10"
 
 
 def test_rucio_no_namespace():
@@ -51,11 +59,26 @@ def test_rucio_no_namespace():
 def test_file_list():
     did = FileListDataset(["c:/foo.bar"])
     assert did.files == ["c:/foo.bar"]
+    assert did.describe() == "1 file: c:/foo.bar"
 
 
 def test_single_file():
     did = FileListDataset("c:/foo.bar")
     assert did.files == ["c:/foo.bar"]
+    assert did.describe() == "1 file: c:/foo.bar"
+
+
+def test_file_list_multiple_preview():
+    did = FileListDataset(["file1.root", "file2.root", "file3.root"])
+
+    assert did.describe() == "3 files: file1.root, file2.root, file3.root"
+
+
+def test_file_list_ellipsis_for_many_files():
+    files = ["file1.root", "file2.root", "file3.root", "file4.root"]
+    did = FileListDataset(files)
+
+    assert did.describe() == "4 files: file1.root, file2.root, file3.root, ..."
 
 
 def test_populate_transform_request(transform_request):
@@ -66,3 +89,23 @@ def test_populate_transform_request(transform_request):
     did2 = RucioDatasetIdentifier("abc:123-456")
     did2.populate_transform_request(transform_request)
     assert transform_request.did == "rucio://abc:123-456"
+
+
+def test_cern_open_data_description():
+    did = CERNOpenDataDatasetIdentifier(12345)
+    assert did.describe() == "cernopendata://12345"
+
+
+def test_cern_open_data_description_with_file_limit():
+    did = CERNOpenDataDatasetIdentifier(12345, num_files=2)
+    assert did.describe() == "cernopendata://12345?files=2"
+
+
+def test_xrootd_description():
+    did = XRootDDatasetIdentifier("root://server//data/*.root")
+    assert did.describe() == "xrootd://root://server//data/*.root"
+
+
+def test_xrootd_description_with_file_limit():
+    did = XRootDDatasetIdentifier("root://server//data/*.root", num_files=1)
+    assert did.describe() == "xrootd://root://server//data/*.root?files=1"