Add records.search RPC function

[mathemancer]

Fixes #3707

This adds a records.search RPC function.

Technical details

The function is documented as usual, and it should be possible to review this with no further explanation. If not, request a documentation improvement.

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[mathemancer]

@Anish9901 This is ready for review, but I'm marking it as a draft to keep us from merging until #3700 is merged.

[Anish9901]

This looks great logic wise @mathemancer, there are some unhandled edge cases that break the function. Please see my specific comments.

[Anish9901]

I think we could avoid this function call when the search list is empty. Assuming frontend already has the records from records.list.

[mathemancer]

We could, but I'd rather have the front end do that. I.e., if they want to avoid the call, they should just not send the request until there are letters in the array. For the completeness of this function I'd really rather treat it as a kind of "narrowing filter" concept. And for that, we should return unfiltered results whenever we get an empty search definition.

[Anish9901]

For some reason having NULL for limit_ here doesn't return anything, But works perfectly in list_records_from_table.

[mathemancer]

Now it returns all matching records.

[Anish9901]

SELECT msar.search_records_from_table(2254321, '[]'::jsonb, 4);
ERROR:  syntax error at or near ">"

Passing an empty json for search_ and a non null value for limit_ also breaks the function and results in a syntax error.

[mathemancer]

Empty or null values for the search def now return unfiltered results.

[Anish9901]

Can we consider storing the result for this function into a variable instead of calling it twice?

[mathemancer]

I did a quick experiment. The variable idea had no noticeable effect, but setting the get_score_expr function to STABLE did. So, I went with that.