Add support for foreign key constraints and foreign key actions#791
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sheaf wants to merge 1 commit intohaskell-beam:masterfrom
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Add support for foreign key constraints and foreign key actions#791sheaf wants to merge 1 commit intohaskell-beam:masterfrom
sheaf wants to merge 1 commit intohaskell-beam:masterfrom
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I am really swamped right now so I won't be able to review this for some time. Hopefully someone else can take a look |
LaurentRDC
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Thanks for your contribution! This is looking solid.
| :: IsSql92ForeignKeyTableConstraintSyntax (BeamSqlBackendTableConstraintSyntax be) | ||
| => ForeignKeySupport be | ||
| -- | The backend does not support @FOREIGN KEY@ constraints. | ||
| ForeignKeyUnsupported :: ForeignKeySupport be |
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I'm actually curious if there are any SQL DBMs that do not support foreign keys.
I know some backends (e.g. SQLite) may ignore these constraints, but I wouldn't say they're unsupported.
This commit adds support for foreign key constraints and actions to
`beam-migrate`, with support in the Postgres and SQLite backends:
- The `ForeignKeyAction` datatype is used to represent possible
actions to perform when updating or deleting a row with referencing
foreign keys.
- `createTableActionProvider` now takes an additional
`ForeignKeySupport` argument: a witness of evidence for
`IsSql92ForeignKeyTableConstraintSyntax` for backends that
support it.
- Postgres and SQLite support for parsing existing foreign key
constraints.
- Introduce the `addTableForeignKey` function for declaring new
foreign key constraints.
LaurentRDC
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Apr 11, 2026
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| -- Note: this does not support cycles in the foreign key reference graph, | ||
| -- for which we would need ALTER TABLE ADD CONSTRAINT, which we don't | ||
| -- currently support. |
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Does the current design prevent adding this support in a later patch? What would be needed to get it working?
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I don't think the current patch would prevent that enhancement. I believe we would need to:
- add a new typeclass, with an instance for Postgres,
- update this logic to allow declaring foreign key constraints that refer to tables that don't exist yet; it would need to branch on whether ALTER TABLE ADD CONSTRAINT is supported, which seems like it would require another GADT like
ForeignKeySupport - add a provider that generates the appropriate ALTER TABLE syntax for foreign key constraints that remain unfulfilled
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This PR adds support for foreign key constraints and actions to
beam-migrate, with support in the Postgres and SQLite backends.ForeignKeyActiondatatype is used to represent possible actions to perform when updating or deleting a row with referencing foreign keys.createTableActionProvidernow takes an additionalForeignKeySupportargument: a witness of evidence forIsSql92ForeignKeyTableConstraintSyntaxfor backends that support it.addTableForeignKeycan be used to declare new foreign key constraints.