feat(bigquery): allow passing schema as a sequence of dicts

bigquery/google/cloud/bigquery/_helpers.py

@@ -224,21 +224,44 @@ def _row_tuple_from_json(row, schema):
 
     Args:
         row (Dict): A JSON response row to be converted.
-        schema (Tuple): A tuple of :class:`~google.cloud.bigquery.schema.SchemaField`.
+        schema (Sequence[Union[ \
+                :class:`~google.cloud.bigquery.schema.SchemaField`, \
+                Mapping[str, Any] \
+        ]]):  Specification of the field types in ``row``.
 
     Returns:
         Tuple: A tuple of data converted to native types.
     """
+    from google.cloud.bigquery.schema import _to_schema_fields
+
+    schema = _to_schema_fields(schema)
+
     row_data = []
     for field, cell in zip(schema, row["f"]):
         row_data.append(_field_from_json(cell["v"], field))
     return tuple(row_data)
 
 
 def _rows_from_json(values, schema):
-    """Convert JSON row data to rows with appropriate types."""
+    """Convert JSON row data to rows with appropriate types.
+
+    Args:
+        values (Sequence[Dict]): The list of responses (JSON rows) to convert.
+        schema (Sequence[Union[ \
+                :class:`~google.cloud.bigquery.schema.SchemaField`, \
+                Mapping[str, Any] \
+        ]]):
+            The table's schema. If any item is a mapping, its content must be
+            compatible with
+            :meth:`~google.cloud.bigquery.schema.SchemaField.from_api_repr`.
+
+    Returns:
+        List[:class:`~google.cloud.bigquery.Row`]
+    """
     from google.cloud.bigquery import Row
+    from google.cloud.bigquery.schema import _to_schema_fields
 
+    schema = _to_schema_fields(schema)
     field_to_index = _field_to_index_mapping(schema)
     return [Row(_row_tuple_from_json(r, schema), field_to_index) for r in values]
 

bigquery/google/cloud/bigquery/_pandas_helpers.py

@@ -239,7 +239,10 @@ def dataframe_to_bq_schema(dataframe, bq_schema):
     Args:
         dataframe (pandas.DataFrame):
             DataFrame for which the client determines the BigQuery schema.
-        bq_schema (Sequence[google.cloud.bigquery.schema.SchemaField]):
+        bq_schema (Sequence[Union[ \
+            :class:`~google.cloud.bigquery.schema.SchemaField`, \
+            Mapping[str, Any] \
+        ]]):
             A BigQuery schema. Use this argument to override the autodetected
             type for some or all of the DataFrame columns.
 
@@ -249,6 +252,7 @@ def dataframe_to_bq_schema(dataframe, bq_schema):
             any column cannot be determined.
     """
     if bq_schema:
+        bq_schema = schema._to_schema_fields(bq_schema)
         for field in bq_schema:
             if field.field_type in schema._STRUCT_TYPES:
                 raise ValueError(
@@ -297,9 +301,12 @@ def dataframe_to_arrow(dataframe, bq_schema):
     Args:
         dataframe (pandas.DataFrame):
             DataFrame to convert to Arrow table.
-        bq_schema (Sequence[google.cloud.bigquery.schema.SchemaField]):
-            Desired BigQuery schema. Number of columns must match number of
-            columns in the DataFrame.
+        bq_schema (Sequence[Union[ \
+            :class:`~google.cloud.bigquery.schema.SchemaField`, \
+            Mapping[str, Any] \
+        ]]):
+            Desired BigQuery schema. The number of columns must match the
+            number of columns in the DataFrame.
 
     Returns:
         pyarrow.Table:
@@ -310,6 +317,8 @@ def dataframe_to_arrow(dataframe, bq_schema):
     column_and_index_names = set(
         name for name, _ in list_columns_and_indexes(dataframe)
     )
+
+    bq_schema = schema._to_schema_fields(bq_schema)
     bq_field_names = set(field.name for field in bq_schema)
 
     extra_fields = bq_field_names - column_and_index_names
@@ -354,7 +363,10 @@ def dataframe_to_parquet(dataframe, bq_schema, filepath, parquet_compression="SN
     Args:
         dataframe (pandas.DataFrame):
             DataFrame to convert to Parquet file.
-        bq_schema (Sequence[google.cloud.bigquery.schema.SchemaField]):
+        bq_schema (Sequence[Union[ \
+            :class:`~google.cloud.bigquery.schema.SchemaField`, \
+            Mapping[str, Any] \
+        ]]):
             Desired BigQuery schema. Number of columns must match number of
             columns in the DataFrame.
         filepath (str):
@@ -368,6 +380,7 @@ def dataframe_to_parquet(dataframe, bq_schema, filepath, parquet_compression="SN
     if pyarrow is None:
         raise ValueError("pyarrow is required for BigQuery schema conversion.")
 
+    bq_schema = schema._to_schema_fields(bq_schema)
     arrow_table = dataframe_to_arrow(dataframe, bq_schema)
     pyarrow.parquet.write_table(arrow_table, filepath, compression=parquet_compression)
 
@@ -388,20 +401,24 @@ def _tabledata_list_page_to_arrow(page, column_names, arrow_types):
     return pyarrow.RecordBatch.from_arrays(arrays, names=column_names)
 
 
-def download_arrow_tabledata_list(pages, schema):
+def download_arrow_tabledata_list(pages, bq_schema):
     """Use tabledata.list to construct an iterable of RecordBatches.
 
     Args:
         pages (Iterator[:class:`google.api_core.page_iterator.Page`]):
             An iterator over the result pages.
-        schema (Sequence[google.cloud.bigquery.schema.SchemaField]):
+        bq_schema (Sequence[Union[ \
+            :class:`~google.cloud.bigquery.schema.SchemaField`, \
+            Mapping[str, Any] \
+        ]]):
             A decription of the fields in result pages.
     Yields:
         :class:`pyarrow.RecordBatch`
         The next page of records as a ``pyarrow`` record batch.
     """
-    column_names = bq_to_arrow_schema(schema) or [field.name for field in schema]
-    arrow_types = [bq_to_arrow_data_type(field) for field in schema]
+    bq_schema = schema._to_schema_fields(bq_schema)
+    column_names = bq_to_arrow_schema(bq_schema) or [field.name for field in bq_schema]
+    arrow_types = [bq_to_arrow_data_type(field) for field in bq_schema]
 
     for page in pages:
         yield _tabledata_list_page_to_arrow(page, column_names, arrow_types)
@@ -422,9 +439,26 @@ def _tabledata_list_page_to_dataframe(page, column_names, dtypes):
     return pandas.DataFrame(columns, columns=column_names)
 
 
-def download_dataframe_tabledata_list(pages, schema, dtypes):
-    """Use (slower, but free) tabledata.list to construct a DataFrame."""
-    column_names = [field.name for field in schema]
+def download_dataframe_tabledata_list(pages, bq_schema, dtypes):
+    """Use (slower, but free) tabledata.list to construct a DataFrame.
+
+    Args:
+        pages (Iterator[:class:`google.api_core.page_iterator.Page`]):
+            An iterator over the result pages.
+        bq_schema (Sequence[Union[ \
+            :class:`~google.cloud.bigquery.schema.SchemaField`, \
+            Mapping[str, Any] \
+        ]]):
+            A decription of the fields in result pages.
+        dtypes(Mapping[str, numpy.dtype]):
+            The types of columns in result data to hint construction of the
+            resulting DataFrame. Not all column types have to be specified.
+    Yields:
+        :class:`pandas.DataFrame`
+        The next page of records as a ``pandas.DataFrame`` record batch.
+    """
+    bq_schema = schema._to_schema_fields(bq_schema)
+    column_names = [field.name for field in bq_schema]
     for page in pages:
         yield _tabledata_list_page_to_dataframe(page, column_names, dtypes)
 

bigquery/google/cloud/bigquery/job.py

@@ -38,6 +38,7 @@
 from google.cloud.bigquery.retry import DEFAULT_RETRY
 from google.cloud.bigquery.routine import RoutineReference
 from google.cloud.bigquery.schema import SchemaField
+from google.cloud.bigquery.schema import _to_schema_fields
 from google.cloud.bigquery.table import _EmptyRowIterator
 from google.cloud.bigquery.table import RangePartitioning
 from google.cloud.bigquery.table import _table_arg_to_table_ref
@@ -1225,8 +1226,10 @@ def range_partitioning(self, value):
 
     @property
     def schema(self):
-        """List[google.cloud.bigquery.schema.SchemaField]: Schema of the
-        destination table.
+        """Sequence[Union[ \
+            :class:`~google.cloud.bigquery.schema.SchemaField`, \
+            Mapping[str, Any] \
+        ]]: Schema of the destination table.
 
         See
         https://cloud.google.com/bigquery/docs/reference/rest/v2/Job#JobConfigurationLoad.FIELDS.schema
@@ -1242,8 +1245,8 @@ def schema(self, value):
             self._del_sub_prop("schema")
             return
 
-        if not all(hasattr(field, "to_api_repr") for field in value):
-            raise ValueError("Schema items must be fields")
+        value = _to_schema_fields(value)
+
         _helpers._set_sub_prop(
             self._properties,
             ["load", "schema", "fields"],

bigquery/google/cloud/bigquery/schema.py

@@ -14,6 +14,8 @@
 
 """Schemas for BigQuery tables / queries."""
 
+import collections
+
 from google.cloud.bigquery_v2 import types
 
 
@@ -256,3 +258,36 @@ def _build_schema_resource(fields):
         Sequence[Dict]: Mappings describing the schema of the supplied fields.
     """
     return [field.to_api_repr() for field in fields]
+
+
+def _to_schema_fields(schema):
+    """Coerce `schema` to a list of schema field instances.
+
+    Args:
+        schema(Sequence[Union[ \
+            :class:`~google.cloud.bigquery.schema.SchemaField`, \
+            Mapping[str, Any] \
+        ]]):
+            Table schema to convert. If some items are passed as mappings,
+            their content must be compatible with
+            :meth:`~google.cloud.bigquery.schema.SchemaField.from_api_repr`.
+
+    Returns:
+        Sequence[:class:`~google.cloud.bigquery.schema.SchemaField`]
+
+    Raises:
+        Exception: If ``schema`` is not a sequence, or if any item in the
+        sequence is not a :class:`~google.cloud.bigquery.schema.SchemaField`
+        instance or a compatible mapping representation of the field.
+    """
+    for field in schema:
+        if not isinstance(field, (SchemaField, collections.Mapping)):
+            raise ValueError(
+                "Schema items must either be fields or compatible "
+                "mapping representations."
+            )
+
+    return [
+        field if isinstance(field, SchemaField) else SchemaField.from_api_repr(field)
+        for field in schema
+    ]

bigquery/google/cloud/bigquery/table.py

@@ -51,9 +51,9 @@
 import google.cloud._helpers
 from google.cloud.bigquery import _helpers
 from google.cloud.bigquery import _pandas_helpers
-from google.cloud.bigquery.schema import SchemaField
 from google.cloud.bigquery.schema import _build_schema_resource
 from google.cloud.bigquery.schema import _parse_schema_resource
+from google.cloud.bigquery.schema import _to_schema_fields
 from google.cloud.bigquery.external_config import ExternalConfig
 from google.cloud.bigquery.encryption_configuration import EncryptionConfiguration
 
@@ -305,8 +305,13 @@ class Table(object):
             A pointer to a table. If ``table_ref`` is a string, it must
             included a project ID, dataset ID, and table ID, each separated
             by ``.``.
-        schema (List[google.cloud.bigquery.schema.SchemaField]):
-            The table's schema
+        schema (Optional[Sequence[Union[ \
+                :class:`~google.cloud.bigquery.schema.SchemaField`, \
+                Mapping[str, Any] \
+        ]]]):
+            The table's schema. If any item is a mapping, its content must be
+            compatible with
+            :meth:`~google.cloud.bigquery.schema.SchemaField.from_api_repr`.
     """
 
     _PROPERTY_TO_API_FIELD = {
@@ -369,13 +374,17 @@ def require_partition_filter(self, value):
 
     @property
     def schema(self):
-        """List[google.cloud.bigquery.schema.SchemaField]: Table's schema.
+        """Sequence[Union[ \
+                :class:`~google.cloud.bigquery.schema.SchemaField`, \
+                Mapping[str, Any] \
+        ]]:
+            Table's schema.
 
         Raises:
-            TypeError: If 'value' is not a sequence
-            ValueError:
-                If any item in the sequence is not a
-                :class:`~google.cloud.bigquery.schema.SchemaField`
+            Exception:
+                If ``schema`` is not a sequence, or if any item in the sequence
+                is not a :class:`~google.cloud.bigquery.schema.SchemaField`
+                instance or a compatible mapping representation of the field.
         """
         prop = self._properties.get("schema")
         if not prop:
@@ -387,9 +396,8 @@ def schema(self):
     def schema(self, value):
         if value is None:
             self._properties["schema"] = None
-        elif not all(isinstance(field, SchemaField) for field in value):
-            raise ValueError("Schema items must be fields")
         else:
+            value = _to_schema_fields(value)
             self._properties["schema"] = {"fields": _build_schema_resource(value)}
 
     @property
@@ -1284,6 +1292,13 @@ class RowIterator(HTTPIterator):
         api_request (Callable[google.cloud._http.JSONConnection.api_request]):
             The function to use to make API requests.
         path (str): The method path to query for the list of items.
+        schema (Sequence[Union[ \
+                :class:`~google.cloud.bigquery.schema.SchemaField`, \
+                Mapping[str, Any] \
+        ]]):
+            The table's schema. If any item is a mapping, its content must be
+            compatible with
+            :meth:`~google.cloud.bigquery.schema.SchemaField.from_api_repr`.
         page_token (str): A token identifying a page in a result set to start
             fetching results from.
         max_results (int, optional): The maximum number of results to fetch.
@@ -1328,6 +1343,7 @@ def __init__(
             page_start=_rows_page_start,
             next_token="pageToken",
         )
+        schema = _to_schema_fields(schema)
         self._field_to_index = _helpers._field_to_index_mapping(schema)
         self._page_size = page_size
         self._preserve_order = False

bigquery/samples/query_external_sheets_permanent_table.py

@@ -52,8 +52,8 @@ def query_external_sheets_permanent_table(dataset_id):
     external_config.source_uris = [sheet_url]
     external_config.options.skip_leading_rows = 1  # Optionally skip header row.
     external_config.options.range = (
-        "us-states!A20:B49"
-    )  # Optionally set range of the sheet to query from.
+        "us-states!A20:B49"  # Optionally set range of the sheet to query from.
+    )
     table.external_data_configuration = external_config
 
     # Create a permanent table linked to the Sheets file.

bigquery/samples/query_external_sheets_temporary_table.py

@@ -49,8 +49,8 @@ def query_external_sheets_temporary_table():
     ]
     external_config.options.skip_leading_rows = 1  # Optionally skip header row.
     external_config.options.range = (
-        "us-states!A20:B49"
-    )  # Optionally set range of the sheet to query from.
+        "us-states!A20:B49"  # Optionally set range of the sheet to query from.
+    )
     table_id = "us_states"
     job_config = bigquery.QueryJobConfig()
     job_config.table_definitions = {table_id: external_config}