Process record summaries in DB layer

[seancolsen]

Before reviewing this PR, make sure you're familiar with the Propose changes to record summaries for beta.

Examples

These examples use the Library Management data, with the following id values:

• "Books" (oid: 36147)

  • "Title"(attnum: 2)
  • "Author" (attnum:10)

• "Authors"

  • "First Name" (attnum: 2)
  • "Last Name" (attnum: 3)

Auto-generated Books summaries

select * from msar.get_record_summaries(36147, array[4,9,15,21,35]);

id	record_summary
4	Abhorsen
15	A Civil Contract
21	A Darkness at Sethanon
9	Academ's Fury
35	Alexander Hamilton

Manually-templated Books summaries

select * from msar.get_record_summaries(
  36147,
  array[4,9,15,21,35],
  '[[2], ", by ", [10, 2], " ", [10, 3]]'::jsonb
);

id	record_summary
4	Abhorsen, by Garth Nix
15	A Civil Contract, by Georgette Heyer
21	A Darkness at Sethanon, by Raymond E Feist
9	Academ's Fury, by Jim Butcher
35	Alexander Hamilton, by Ron Chernow

Thoughts

• I feel the least confident about the implementation within get_record_summaries_via_query. Very much open to different approaches there, including changing the approach of passing id values in via array.

• On a similar note, I wrote a test __SKIP__test_record_summary_performance. This is skipped because it's failing. The intent of this test is to verify that we're only generating record summaries for the records passed in via the array. But... (sad trombone)... it doesn't actually work like I thought it would. My next step here is to dig into EXPLAIN to get a better sense of the query plan. I thought Postgres would be smarter here, but oh well.

  This empirical evidence does make me question my original premise with this design. I was hoping that we'd be able to define a bespoke record summary query for a specific table — devoid of any filtering — and then use that at the inner layer to compose the filtered query using application-defined logic. Alas, it may be that the bespoke queries actually need to be aware of the filtering. I'd like to experiment with this more and bounce some ideas around with you.

  For the time being, this works. But I'd like to eventually make it faster. In theory we could potentially kick that can down the road.

• Are there some types which wouldn't be able to cast to TEXT via cast( v AS text )? I don't understand enough about how this works in Postgres. It seems like there is a difference between implicit casting and explict casting, or something like that. I did a little research but didn't find the answers I was looking for. I did write a test test_record_summary_with_no_text_columns, which asserts that we can auto generate record summaries for a table having only uuid and point column types. This actually led me to make the fix in 9cca125. I'm hoping this will cover all possible types, but I think you would know better.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

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[seancolsen]

@mathemancer this is ready for a proper review now.

[seancolsen]

Oh I also meant to mention that I rebased this on top of #3556 — but only for the sake of convenience during development (so that I could see/run/copy your tests in that PR). I can rebase this back on another branch if you prefer.