BigQuery: Allow cross-project queries

[tswast]

It would be great if there was a way to submit query jobs to one project, but allow querying jobs in another project.

I tried querying the StackOverflow public dataset like this:

con = ibis.bigquery.connect(
    project_id='swast-scratch',
    dataset_id='bigquery-public-data.stackoverflow')
table = con.table('posts_questions')
expr = table[table.tags.contains('ibis')][['title', 'tags']]
print(expr)

and got the following error:

$ python ibis_bigquery.py
Traceback (most recent call last):
  File "ibis_bigquery.py", line 20, in <module>
    table = con.table('posts_questions')
  File "/Users/swast/.pyenv/versions/3.6.4/envs/ibis-stable/lib/python3.6/site-packages/ibis/bigquery/client.py", line 281, in table
    t = super(BigQueryClient, self).table(*args, **kwargs)
  File "/Users/swast/.pyenv/versions/3.6.4/envs/ibis-stable/lib/python3.6/site-packages/ibis/client.py", line 119, in table
    schema = self._get_table_schema(qualified_name)
  File "/Users/swast/.pyenv/versions/3.6.4/envs/ibis-stable/lib/python3.6/site-packages/ibis/bigquery/client.py", line 304, in _get_table_schema
    return self.get_schema(qualified_name)
  File "/Users/swast/.pyenv/versions/3.6.4/envs/ibis-stable/lib/python3.6/site-packages/ibis/bigquery/client.py", line 363, in get_schema
    (table_id, dataset_id) = _ensure_split(name, database)
  File "/Users/swast/.pyenv/versions/3.6.4/envs/ibis-stable/lib/python3.6/site-packages/ibis/bigquery/client.py", line 32, in _ensure_split
    assert len(split) == 2
AssertionError

Note: I also tried:

con = ibis.bigquery.connect(project_id='bigquery-public-data', dataset_id='stackoverflow')
table = con.table('posts_questions')
expr = table[table.tags.contains('ibis')][['title', 'tags']]
print(expr)

but I got this error:

google.api.core.exceptions.Forbidden: 403 POST https://www.googleapis.com/bigquery/v2/projects/bigquery-public-data/queries: Access Denied: Project bigquery-public-data: The user macbook@swast-scratch.iam.gserviceaccount.com does not have bigquery.jobs.create permission in project bigquery-public-data.

I'd actually expect this second one as I do not have permission to charge queries to the bigquery-public-data project, but I should have permission to run queries against those tables (charging to my own project).

[cpcloud]

This is up next after the 1.0.0 merge

[tswast]

I wonder if project_id in the ibis.bigquery.connect becomes ambiguous if we do this? One way to disambiguate might be to have folks pass in a google.cloud.bigquery.Client object in the cases when they want the project_id of the tables they query to be different from the project they want to charge queries to.