Bigquery: Add page_size parameter to QueryJob.result.

[AzemaBaptiste]

Makes the user control page size for a bigquery job.

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and have the pull request author add another comment and the bot will run again. If the bot doesn't comment, it means it doesn't think anything has changed.

ℹ️ Googlers: Go here for more info.

[AzemaBaptiste]

I signed it!

[googlebot]

CLAs look good, thanks!

ℹ️ Googlers: Go here for more info.

[tswast]

Coverage failure

tests/unit/test_magics.py                     327      0      4      1    99%   242->exit

is unrelated to this change and was fixed in #8179

[tswast]

Let's assert that tabledata.list is called with the right page size (maxResults) as a parameter.

See:

google-cloud-python/bigquery/tests/unit/test_client.py

Line 4197 in 0975724

def test_list_rows(self):

Specifically, I'd like to see something like:

tabledata_path = "/projects/%s/datasets/%s/tables/%s/data" % (
    self.PROJECT,
    self.DS_ID,
    self.TABLE_ID,
)
conn.api_request.assert_called_once_with(
    method="GET", path=tabledata_path, query_params={"maxResults": 3}
)

[AzemaBaptiste]

Hello Tim,
Thanks for the feedback but I think I need a hand.
Do you mean that the maxResults should be directly linked to the page_size ? The api documentation seems to say it link but the code don't

google-cloud-python/bigquery/google/cloud/bigquery/client.py

Lines 1949 to 1963 in 0975724

	row_iterator = RowIterator(
	client=self,
	api_request=functools.partial(self._call_api, retry),
	path="%s/data" % (table.path,),
	schema=schema,
	page_token=page_token,
	max_results=max_results,
	page_size=page_size,
	extra_params=params,
	table=table,
	# Pass in selected_fields separately from schema so that full
	# tables can be fetched without a column filter.
	selected_fields=selected_fields,
	)
	return row_iterator

[tswast]

Confusingly, page_size in Python is used to set maxResults in the API request, since that's what BigQuery calls its page size parameter.

I've updated your PR to test for this.

[AzemaBaptiste]

Okay I see...
Many thanks for the help on the unit test !

[tswast]

Thanks for the contribution @AzemaBaptiste. This is a great addition.

I like the system test. I'd just like to also verify in a unit test that the parameter is actually sent.

[bokub]

Great job, thanks 🎉