_group_count= feature improvements

[simonw]

• The "apply filters" form should keep you on the _group_count= page
• Foreign key references should be expand
• Page title should reflect the view you are on

[simonw]

The single biggest challenge here is expanding foreign key references. This is the blocker that prevents _group_count from being useful at the moment.

[simonw]

From a code point of view, the current mechanism for _group_count makes the TableView even more complicated:

datasette/datasette/app.py

Lines 644 to 653 in 446d47f

	# _group_count=col1&_group_count=col2
	group_count = special_args_lists.get('_group_count') or []
	if group_count:
	count_sql = None
	sql = 'select {group_cols}, count(*) as "count" from {table_name} {where} group by {group_cols} order by "count" desc limit 100'.format(
	group_cols=', '.join('"{}"'.format(group_count_col) for group_count_col in group_count),
	table_name=escape_sqlite(table),
	where=where_clause,
	)
	is_view = True

Instead, I think if _group_count is detected we should generate the SQL and then defer to self.custom_sql, like we do for canned queries:

datasette/datasette/app.py

Lines 539 to 541 in 446d47f

	canned_query = self.ds.get_canned_query(name, table)
	if canned_query is not None:
	return await self.custom_sql(request, name, hash, canned_query['sql'], editable=False, canned_query=table)

[simonw]

Closing this as obsolete since we have facets now.