Raise with extra or missing columns in load_table_from_dataframe sc…

…hema. (googleapis#9096)

I found it to be difficult to debug typos in column/index names in the
schema, so I have hardened the error messages to indicate when unknown
field values are found.

bigquery/google/cloud/bigquery/_pandas_helpers.py

@@ -211,15 +211,18 @@ def dataframe_to_bq_schema(dataframe, bq_schema):
                     "https://github.com/googleapis/google-cloud-python/issues/8191"
                 )
         bq_schema_index = {field.name: field for field in bq_schema}
+        bq_schema_unused = set(bq_schema_index.keys())
     else:
         bq_schema_index = {}
+        bq_schema_unused = set()
 
     bq_schema_out = []
     for column, dtype in zip(dataframe.columns, dataframe.dtypes):
         # Use provided type from schema, if present.
         bq_field = bq_schema_index.get(column)
         if bq_field:
             bq_schema_out.append(bq_field)
+            bq_schema_unused.discard(bq_field.name)
             continue
 
         # Otherwise, try to automatically determine the type based on the
@@ -230,6 +233,15 @@ def dataframe_to_bq_schema(dataframe, bq_schema):
             return None
         bq_field = schema.SchemaField(column, bq_type)
         bq_schema_out.append(bq_field)
+
+    # Catch any schema mismatch. The developer explicitly asked to serialize a
+    # column, but it was not found.
+    if bq_schema_unused:
+        raise ValueError(
+            "bq_schema contains fields not present in dataframe: {}".format(
+                bq_schema_unused
+            )
+        )
     return tuple(bq_schema_out)
 
 
@@ -248,9 +260,21 @@ def dataframe_to_arrow(dataframe, bq_schema):
             Table containing dataframe data, with schema derived from
             BigQuery schema.
     """
-    if len(bq_schema) != len(dataframe.columns):
+    column_names = set(dataframe.columns)
+    bq_field_names = set(field.name for field in bq_schema)
+
+    extra_fields = bq_field_names - column_names
+    if extra_fields:
+        raise ValueError(
+            "bq_schema contains fields not present in dataframe: {}".format(
+                extra_fields
+            )
+        )
+
+    missing_fields = column_names - bq_field_names
+    if missing_fields:
         raise ValueError(
-            "Number of columns in schema must match number of columns in dataframe."
+            "bq_schema is missing fields from dataframe: {}".format(missing_fields)
         )
 
     arrow_arrays = []

bigquery/tests/unit/test__pandas_helpers.py

@@ -609,12 +609,26 @@ def test_dataframe_to_parquet_without_pyarrow(module_under_test, monkeypatch):
 
 @pytest.mark.skipif(pandas is None, reason="Requires `pandas`")
 @pytest.mark.skipif(pyarrow is None, reason="Requires `pyarrow`")
-def test_dataframe_to_parquet_w_missing_columns(module_under_test, monkeypatch):
+def test_dataframe_to_parquet_w_extra_fields(module_under_test, monkeypatch):
     with pytest.raises(ValueError) as exc_context:
         module_under_test.dataframe_to_parquet(
-            pandas.DataFrame(), (schema.SchemaField("not_found", "STRING"),), None
+            pandas.DataFrame(), (schema.SchemaField("not_in_df", "STRING"),), None
         )
-    assert "columns in schema must match" in str(exc_context.value)
+    message = str(exc_context.value)
+    assert "bq_schema contains fields not present in dataframe" in message
+    assert "not_in_df" in message
+
+
+@pytest.mark.skipif(pandas is None, reason="Requires `pandas`")
+@pytest.mark.skipif(pyarrow is None, reason="Requires `pyarrow`")
+def test_dataframe_to_parquet_w_missing_fields(module_under_test, monkeypatch):
+    with pytest.raises(ValueError) as exc_context:
+        module_under_test.dataframe_to_parquet(
+            pandas.DataFrame({"not_in_bq": [1, 2, 3]}), (), None
+        )
+    message = str(exc_context.value)
+    assert "bq_schema is missing fields from dataframe" in message
+    assert "not_in_bq" in message
 
 
 @pytest.mark.skipif(pandas is None, reason="Requires `pandas`")

bigquery/tests/unit/test_client.py

@@ -5517,7 +5517,6 @@ def test_load_table_from_dataframe_w_partial_schema(self):
     @unittest.skipIf(pandas is None, "Requires `pandas`")
     @unittest.skipIf(pyarrow is None, "Requires `pyarrow`")
     def test_load_table_from_dataframe_w_partial_schema_extra_types(self):
-        from google.cloud.bigquery.client import _DEFAULT_NUM_RETRIES
         from google.cloud.bigquery import job
         from google.cloud.bigquery.schema import SchemaField
 
@@ -5540,31 +5539,17 @@ def test_load_table_from_dataframe_w_partial_schema_extra_types(self):
             SchemaField("unknown_col", "BYTES"),
         )
         job_config = job.LoadJobConfig(schema=schema)
-        with load_patch as load_table_from_file:
+        with load_patch as load_table_from_file, pytest.raises(
+            ValueError
+        ) as exc_context:
             client.load_table_from_dataframe(
                 dataframe, self.TABLE_REF, job_config=job_config, location=self.LOCATION
             )
 
-        load_table_from_file.assert_called_once_with(
-            client,
-            mock.ANY,
-            self.TABLE_REF,
-            num_retries=_DEFAULT_NUM_RETRIES,
-            rewind=True,
-            job_id=mock.ANY,
-            job_id_prefix=None,
-            location=self.LOCATION,
-            project=None,
-            job_config=mock.ANY,
-        )
-
-        sent_config = load_table_from_file.mock_calls[0][2]["job_config"]
-        assert sent_config.source_format == job.SourceFormat.PARQUET
-        assert tuple(sent_config.schema) == (
-            SchemaField("int_col", "INTEGER"),
-            SchemaField("int_as_float_col", "INTEGER"),
-            SchemaField("string_col", "STRING"),
-        )
+        load_table_from_file.assert_not_called()
+        message = str(exc_context.value)
+        assert "bq_schema contains fields not present in dataframe" in message
+        assert "unknown_col" in message
 
     @unittest.skipIf(pandas is None, "Requires `pandas`")
     @unittest.skipIf(pyarrow is None, "Requires `pyarrow`")