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[GH-ISSUE #8867] MySQL inserted id #19849

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opened 2026-04-15 19:12:05 -05:00 by GiteaMirror · 1 comment
GiteaMirror commented 2026-04-15 19:12:05 -05:00
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Originally created by @howlettt on GitHub (Mar 31, 2026).
Original GitHub issue: https://github.com/better-auth/better-auth/issues/8867

Originally assigned to: @ping-maxwell on GitHub.

Noticed the following code that relies on finding the inserted row based on the largest id, which could fail in a high load scenario when another new row is inserted before the select finishes. I believe the inserted id is returned when using MySQL via the insertId member on the response, so this could be improved.

https://github.com/better-auth/better-auth/blob/85e37693a2766c7560c50d7ab675adfba8c681a2/packages/kysely-adapter/src/kysely-adapter.ts#L113-L144

Originally created by @howlettt on GitHub (Mar 31, 2026). Original GitHub issue: https://github.com/better-auth/better-auth/issues/8867 Originally assigned to: @ping-maxwell on GitHub. Noticed the following code that relies on finding the inserted row based on the largest id, which could fail in a high load scenario when another new row is inserted before the select finishes. I believe the inserted id is returned when using MySQL via the `insertId` member on the response, so this could be improved. https://github.com/better-auth/better-auth/blob/85e37693a2766c7560c50d7ab675adfba8c681a2/packages/kysely-adapter/src/kysely-adapter.ts#L113-L144
GiteaMirror added the databasebug labels 2026-04-15 19:12:05 -05:00
GiteaMirror commented 2026-04-15 19:12:07 -05:00
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@dosubot[bot] commented on GitHub (Mar 31, 2026):

Hi @howlettt! I'm Dosu and I’m helping the better-auth team.

Good catch — you're right that this is a real race condition, and you're also right that Kysely already exposes insertId on its QueryResult interface (as a bigint) for MySQL auto-increment inserts [1]. The current code simply discards the result of await builder.execute() instead of capturing it [2].

A fix for the auto-increment case could be as straightforward as:

const result = await builder.execute();
const insertId = result[0]?.insertId;
if (insertId) {
  res = await db
    .selectFrom(model)
    .selectAll()
    .where(getFieldName({ model, field: "id" }), "=", Number(insertId))
    .executeTakeFirst();
  return res;
}

For context, PR #6634 previously proposed a fix for this (including LAST_INSERT_ID() usage and race condition tests), but it was closed without merging. The current recommended workaround is to provide a custom generateId function so the ID is known before the insert, making the follow-up SELECT reliable [3].

Worth noting this insertId approach only helps with auto-increment integer PKs — UUID/CUID keys generated at the DB level would still need a different strategy.

To reply, just mention @dosu.

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<!-- gh-comment-id:4166210384 --> @dosubot[bot] commented on GitHub (Mar 31, 2026): <!-- Greeting --> Hi @howlettt! I'm [Dosu](https://go.dosu.dev/dosubot) and I’m helping the better-auth team. <!-- Answer --> Good catch — you're right that this is a real race condition, and you're also right that Kysely already exposes `insertId` on its `QueryResult` interface (as a `bigint`) for MySQL auto-increment inserts [[1]](https://raw.githubusercontent.com/kysely-org/kysely/master/src/driver/database-connection.ts). The current code simply discards the result of `await builder.execute()` instead of capturing it [[2]](https://github.com/better-auth/better-auth/blob/df7f8dda9f884a486f05d6cc91dfe53b8f34e7a9/packages/kysely-adapter/src/kysely-adapter.ts#L113-L114). A fix for the auto-increment case could be as straightforward as: ```typescript const result = await builder.execute(); const insertId = result[0]?.insertId; if (insertId) { res = await db .selectFrom(model) .selectAll() .where(getFieldName({ model, field: "id" }), "=", Number(insertId)) .executeTakeFirst(); return res; } ``` For context, [PR #6634](https://github.com/better-auth/better-auth/pull/6634) previously proposed a fix for this (including `LAST_INSERT_ID()` usage and race condition tests), but it was closed without merging. The current recommended workaround is to provide a custom `generateId` function so the ID is known *before* the insert, making the follow-up SELECT reliable [[3]](https://github.com/better-auth/better-auth/issues/1480#issuecomment-2744359832). Worth noting this `insertId` approach only helps with auto-increment integer PKs — UUID/CUID keys generated at the DB level would still need a different strategy. <!-- Dosu Comment Footer --> *To reply, just mention [@dosu](https://go.dosu.dev/dosubot?utm_source=github&utm_medium=bot-comment&utm_campaign=github-assistant&utm_content=brand-link).* --- <sup>How did I do? 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Reference: github-starred/better-auth#19849