[fm] Introduce SitrepGuardedInsert.#10532
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Add the `SitrepGuardedInsert` Diesel combinator and the
`SitrepGuardedResource` trait: a generic primitive for FM rendezvous to
insert a resource row idempotently and guarded against stale-sitrep
execution.
The combinator wraps a caller-supplied resource INSERT in a single CTE
statement that:
- aborts (StaleSitrep) unless the executor's expected generation still
equals the latest sitrep's generation column;
- short-circuits (AlreadyExists) if a creation marker already exists for
the resource id;
- on a successful insert, atomically writes a creation marker, gated by
`WHERE EXISTS (SELECT 1 FROM new_resource)` so a marker is never
fabricated for a pre-existing row.
All spliced SQL identifiers come from the trait's `&'static str` consts, so
the query is injection-safe. The result is surfaced as a
`SitrepGuardedInsertOutcome` of Created / AlreadyExists / StaleSitrep.
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| /// 5. `new_marker`: the marker INSERT, emitted inline by the | ||
| /// combinator using R's `&'static str` consts. This only runs when | ||
| /// `new_resource` actually produced a row. | ||
| fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, Pg>) -> QueryResult<()> { |
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It would be nice to have an expectorate test (and maybe also an EXPLAIN test) for the kind of queries that this generates.
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I've added an expectorate test in 365af00. I didn't bother with an EXPLAIN test yet, but I'm pondering it...
- generate table and column names from types, rather than hardcoding them as static strings - add expectorate test - use `Generation` type for generation values - style nit - don't tell lies
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| // Column names injected into the CTEs below. | ||
| let marker_id_column = <R::MarkerIdColumn as Column>::NAME; | ||
| let generation_column = <R::GenerationColumn as Column>::NAME; | ||
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what the fuck github |
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Add the
SitrepGuardedInsertDiesel combinator and theSitrepGuardedResourcetrait: a generic primitive for FM rendezvous to insert a resource row idempotently and guarded against stale-sitrep execution.The combinator wraps a caller-supplied resource INSERT in a single CTE statement that:
The result is surfaced as a
SitrepGuardedInsertOutcomeofCreated/AlreadyExists/StaleSitrep.Context: #10248. This is used in #10533 and #10535 which are split out in hopes of making the review somewhat less miserable.