# 10. Rollback: auto-generated vs explicit

[← 9. Liquibase: anatomy of an update](09-liquibase-anatomy-of-an-update.md) · [Index](../README.md) · Next: [11. Liquibase locking →](11-liquibase-locking.md)

Chapter [7](07-why-there-is-no-undo.md) showed Flyway Community has no working `undo` at all.
Liquibase's answer is `rollback()` — and whether it works depends entirely on the change type.

## When Liquibase can invert a change on its own

`createTable` is one of the change types Liquibase knows how to invert without being told how —
it just runs `DROP TABLE`.
[`LiquibaseRollbackAutoTest`](../src/test/java/com/ankurm/dbmigrations/liquibase/LiquibaseRollbackAutoTest.java)
writes no `rollback:` block anywhere in its changelog, calls `update()`, confirms the `session`
table exists, then calls `rollback(1, ...)`:

```
after update(): session table exists = true
after rollback(1): session table exists = false
```

(from [`docs/output/10-liquibase-rollback-auto.txt`](output/10-liquibase-rollback-auto.txt))

## When it can't

`insert` is not in that list.
[`LiquibaseRollbackFailTest`](../src/test/java/com/ankurm/dbmigrations/liquibase/LiquibaseRollbackFailTest.java)
applies a `createTable` changeset followed by an `insert` changeset, then calls `rollback(1, ...)`
— which only asks to roll back the *most recent* changeset, the insert. It fails for real:

```
after update(): both changesets applied
rollback(1) threw: liquibase.exception.CommandExecutionException
message: liquibase.exception.LiquibaseException: liquibase.exception.RollbackFailedException: liquibase.exception.RollbackImpossibleException: No inverse to liquibase.change.core.InsertDataChange created
```

(from [`docs/output/11-liquibase-rollback-no-inverse.txt`](output/11-liquibase-rollback-no-inverse.txt))

## The fix: write the inverse yourself

[`LiquibaseRollbackExplicitTest`](../src/test/java/com/ankurm/dbmigrations/liquibase/LiquibaseRollbackExplicitTest.java)
is the same `insert` changeset, this time carrying its own `rollback:` block:

```yaml
- insert:
    tableName: audit_log
    columns:
      - {column: {name: event, value: 'system-start'}}
  rollback:
    - delete:
        tableName: audit_log
        where: event='system-start'
```

`rollback(1, ...)` now succeeds — the table stays, the row is gone:

```
audit_log after rollback(1) — table still exists, the row is gone:
ID | EVENT
---+------
(0 rows)
```

(from [`docs/output/12-liquibase-rollback-explicit.txt`](output/12-liquibase-rollback-explicit.txt))

<svg viewBox="0 0 700 160" xmlns="http://www.w3.org/2000/svg" font-family="monospace" font-size="13">
  <rect x="20" y="20" width="200" height="50" rx="6" fill="#dcfce7" stroke="#16a34a"/>
  <text x="120" y="42" text-anchor="middle">createTable</text>
  <text x="120" y="58" text-anchor="middle" font-size="11">auto-invertible → DROP TABLE</text>
  <rect x="250" y="20" width="200" height="50" rx="6" fill="#fee2e2" stroke="#dc2626"/>
  <text x="350" y="42" text-anchor="middle">insert, no rollback:</text>
  <text x="350" y="58" text-anchor="middle" font-size="11">RollbackImpossibleException</text>
  <rect x="480" y="20" width="200" height="50" rx="6" fill="#dcfce7" stroke="#16a34a"/>
  <text x="580" y="42" text-anchor="middle">insert + rollback:</text>
  <text x="580" y="58" text-anchor="middle" font-size="11">works, runs the delete</text>
  <text x="20" y="110" font-size="12" fill="#475569">Whether rollback() works is a property of the CHANGE TYPE and whether you wrote a</text>
  <text x="20" y="128" font-size="12" fill="#475569">rollback: block — not a global Liquibase capability you can rely on by default.</text>
</svg>

## Going deeper

- [Which change types Liquibase can auto-generate a rollback for](https://docs.liquibase.com/workflows/liquibase-community/how-to-apply-or-revert-changes.html) (`rel="nofollow"`) — `createTable`, `addColumn`, and a handful of other structural changes; almost anything involving data (`insert`, `update`, `delete`, most `sql:` changes) needs an explicit `rollback:` block.
- **A team relying on rollback in production is really relying on discipline**: every changeset that touches data needs its rollback written and tested *at the time the changeset is written*, not discovered missing during an actual incident — `rollback(1, ...)` failing is the worst possible moment to learn `insert` has no inverse.
- Liquibase also supports `rollbackCount`, `rollbackToDate` and rolling back by tag — this module exercises only the single-changeset `rollback(int, ...)` overload.