Updating Bigquery inserted timestamps to use seconds.

As stated in the docs
> BigQuery stores TIMESTAMP data internally as a
> UNIX timestamp with microsecond precision
> ...Specifies the number of seconds since the epoch.

Author: dhermes

gcloud/bigquery/table.py

@@ -19,6 +19,7 @@
 import six
 
 from gcloud._helpers import _datetime_from_microseconds
+from gcloud._helpers import _microseconds_from_datetime
 from gcloud._helpers import _millis_from_datetime
 from gcloud.exceptions import NotFound
 from gcloud.bigquery._helpers import _rows_from_json
@@ -654,8 +655,11 @@ def insert_data(self,
             row_info = {}
 
             for field, value in zip(self._schema, row):
-                if field.field_type == 'TIMESTAMP':
-                    value = _millis_from_datetime(value)
+                if field.field_type == 'TIMESTAMP' and value is not None:
+                    # BigQuery stores TIMESTAMP data internally as a
+                    # UNIX timestamp with microsecond precision.
+                    # Specifies the number of seconds since the epoch.
+                    value = _microseconds_from_datetime(value) * 1e-6
                 row_info[field.name] = value
 
             info = {'json': row_info}

gcloud/bigquery/test_table.py

@@ -1060,7 +1060,7 @@ def test_fetch_data_w_record_schema(self):
     def test_insert_data_w_bound_client(self):
         import datetime
         from gcloud._helpers import UTC
-        from gcloud._helpers import _millis_from_datetime
+        from gcloud._helpers import _microseconds_from_datetime
         from gcloud.bigquery.table import SchemaField
 
         WHEN_TS = 1437767599.006
@@ -1084,9 +1084,12 @@ def test_insert_data_w_bound_client(self):
         ]
 
         def _row_data(row):
+            joined = None
+            if row[2] is not None:
+                joined = _microseconds_from_datetime(row[2]) * 1e-6
             return {'full_name': row[0],
                     'age': row[1],
-                    'joined': _millis_from_datetime(row[2])}
+                    'joined': joined}
 
         SENT = {
             'rows': [{'json': _row_data(row)} for row in ROWS],