_facet_array should work against views

[simonw]

I created this view: https://json-view-facet-bug-demo-j7hipcg4aq-uc.a.run.app/russian-ads-8dbda00/ads_with_targets

CREATE VIEW ads_with_targets as select ads.*, json_group_array(targets.name) as target_names from ads
  join ad_targets on ad_targets.ad_id = ads.id
  join targets on ad_targets.target_id = targets.id
  group by ad_targets.ad_id

When I try to apply faceting by array it appears to work at first: https://json-view-facet-bug-demo-j7hipcg4aq-uc.a.run.app/russian-ads/ads_with_targets?_facet_array=target_names

But actually it's doing the wrong thing - the SQL for the facets uses rowid, but rowid is not present on views at all! These results are incorrect, and clicking to select a facet will fail to produce any rows: https://json-view-facet-bug-demo-j7hipcg4aq-uc.a.run.app/russian-ads/ads_with_targets?_facet_array=target_names&target_names__arraycontains=people_who_match%3Ainterests%3AAfrican-American+Civil+Rights+Movement+%281954%E2%80%9468%29

Here's the SQL it should be using when you select a facet (note that it does not use a rowid):

https://json-view-facet-bug-demo-j7hipcg4aq-uc.a.run.app/russian-ads?sql=select+*+from+ads_with_targets+where+id+in+%28%0D%0A++++++++++++select+ads_with_targets.id+from+ads_with_targets%2C+json_each%28ads_with_targets.target_names%29+j%0D%0A++++++++++++where+j.value+%3D+%3Ap0%0D%0A++++++++%29+limit+101&p0=people_who_match%3Ainterests%3ABlack+%28Color%29

So we need to do something a lot smarter here. I'm not sure what the fix will look like, or even if it's feasible given that views don't have a rowid to hook into so the JSON faceting SQL may have to be completely rewritten.

datasette publish cloudrun \
    russian-ads.db \
    --name json-view-facet-bug-demo \
    --branch master \
    --extra-options "--config sql_time_limit_ms:5000 --config facet_time_limit_ms:5000"

[simonw]

It may be that some facet implementations (ArrayFacet in this case) need a way to detect if they are supported by the thing they are running against (must be a rowid table in this case) and avoid suggesting themselves if they are not compatible. This may require a change to the information we make available to the suggest() method (information passed to the Facet class constructor).

[simonw]

I think this SQL recipe may work instead:

select
  *
from
  ads_with_targets
where
  'people_who_match:interests:African-American Civil Rights Movement (1954—68)' in (
    select
      value
    from
      json_each(target_names)
  )
  and 'interests:Martin Luther King III' in (
    select
      value
    from
      json_each(target_names)
  )

https://json-view-facet-bug-demo-j7hipcg4aq-uc.a.run.app/russian-ads?sql=select%0D%0A++*%0D%0Afrom%0D%0A++ads_with_targets%0D%0Awhere%0D%0A++%27people_who_match%3Ainterests%3AAfrican-American+Civil+Rights+Movement+%281954%E2%80%9468%29%27+in+%28%0D%0A++++select%0D%0A++++++value%0D%0A++++from%0D%0A++++++json_each%28target_names%29%0D%0A++%29%0D%0A++and+%27interests%3AMartin+Luther+King+III%27+in+%28%0D%0A++++select%0D%0A++++++value%0D%0A++++from%0D%0A++++++json_each%28target_names%29%0D%0A++%29&interests=&African=&Martin=

[simonw]

Applied that fix to the arraycontains filter but I'm still getting bad results for the faceting:

Should never get 182 results on a page that faceting against only 172 items.

[simonw]

I think this code is wrong in the ArrayFacet class:

datasette/datasette/facets.py

Lines 357 to 364 in 502c02f

	facet_sql = """
	select j.value as value, count(*) as count from (
	{sql}
	) join json_each({col}) j
	group by j.value order by count desc, value limit {limit}
	""".format(
	col=escape_sqlite(column), sql=self.sql, limit=facet_size + 1
	)

[simonw]

It looks like the problem here is that some of the tags occur more than once in the documents:

So they get counted more than once, hence the 182 count for something that couldn't possibly return more than 172 documents.

[simonw]

Given this query: https://json-view-facet-bug-demo-j7hipcg4aq-uc.a.run.app/russian-ads?sql=select%0D%0A++j.value+as+value%2C%0D%0A++count%28*%29+as+count%0D%0Afrom%0D%0A++%28%0D%0A++++select%0D%0A++++++id%2C%0D%0A++++++file%2C%0D%0A++++++clicks%2C%0D%0A++++++impressions%2C%0D%0A++++++text%2C%0D%0A++++++url%2C%0D%0A++++++spend_amount%2C%0D%0A++++++spend_currency%2C%0D%0A++++++created%2C%0D%0A++++++ended%2C%0D%0A++++++target_names%0D%0A++++from%0D%0A++++++ads_with_targets%0D%0A++++where%0D%0A++++++%3Ap0+in+%28%0D%0A++++++++select%0D%0A++++++++++value%0D%0A++++++++from%0D%0A++++++++++json_each%28%5Bads_with_targets%5D.%5Btarget_names%5D%29%0D%0A++++++%29%0D%0A++%29%0D%0A++join+json_each%28target_names%29+j%0D%0Agroup+by%0D%0A++j.value%0D%0Aorder+by%0D%0A++count+desc%2C%0D%0A++value%0D%0Alimit%0D%0A++31&p0=people_who_match%3Ainterests%3AAfrican-American+culture

select
  j.value as value,
  count(*) as count
from
  (
    select
      id,
      file,
      clicks,
      impressions,
      text,
      url,
      spend_amount,
      spend_currency,
      created,
      ended,
      target_names
    from
      ads_with_targets
    where
      :p0 in (
        select
          value
        from
          json_each([ads_with_targets].[target_names])
      )
  )
  join json_each(target_names) j
group by
  j.value
order by
  count desc,
  value
limit
  31

How can I return a count of the number of documents containing each tag, but not the number of total tags that match including duplicates?

[simonw]

This looks like it might work:

with inner as (
  select
    *
  from
    ads_with_targets
  where
    :p0 in (
      select
        value
      from
        json_each([ads_with_targets].[target_names])
    )
),
deduped_array_items as (
  select
    distinct j.value,
    inner.*
  from
    json_each([inner].[target_names]) j
    join inner
)
select
  value,
  count(*)
from
  deduped_array_items
group by
  value
order by
  count(*) desc

[simonw]

It uses a CTE which were introduced in SQLite 3.8 - and AWS Lambda Python 3.9 still provides 3.7 - but I've checked and I can use pysqlite3-binary to work around that there so I'm OK relying on CTEs for this.

[simonw]

I tried this and it seems to work correctly:

        for source_and_config in self.get_configs():
            config = source_and_config["config"]
            source = source_and_config["source"]
            column = config.get("column") or config["simple"]
            facet_sql = """
                with inner as ({sql}),
                deduped_array_items as (
                    select
                        distinct j.value,
                        inner.*
                    from
                        json_each([inner].{col}) j
                        join inner
                )
                select
                    value as value,
                    count(*) as count
                from
                    deduped_array_items
                group by
                    value
                order by
                    count(*) desc limit {limit}
            """.format(
                col=escape_sqlite(column), sql=self.sql, limit=facet_size + 1
            )

The queries are very slow though - I had to bump up to 2s time limit even against only a view returning 3,499 rows.

[simonw]

Actually with the cache warmed up it looks like the facet query is taking 150ms which is good enough.