View Source References

To configure the behavior of generated foreign keys on a resource, we use the references section, within the postgres configuration block.

For example:

postgres do
  # other PostgreSQL config here

  references do
    reference :post, on_delete: :delete, on_update: :update, name: "comments_to_posts_fkey"
  end
end

On Delete

This option describes what to do if the referenced row is deleted.

The option is called on_delete, instead of on_destroy, because it is hooking into the database level deletion, not a destroy action in your resource. See the warning above.

The possible values for the option are :nothing, :restrict, :delete, :nilify, {:nilify, columns}.

With :nothing or :restrict the deletion of the referenced row is prevented.

With :delete the row is deleted together with the referenced row.

With :nilify all columns of the foreign-key constraint are nilified.

With {:nilify, columns} a column list can specify which columns should be set to nil. If you intend to use this option to nilify a subset of the columns, note that it cannot be used together with the match: :full option otherwise a mix of nil and non-nil values would fail the constraint and prevent the deletion of the referenced row. In addition, keep into consideration that this option is only supported from Postgres v15.0 onwards.

On Update

This option describes what to do if the referenced row is updated.

The possible values for the option are :nothing, :restrict, :update, :nilify.

With :nothing or :restrict the update of the referenced row is prevented.

With :update the row is updated according to the referenced row.

With :nilify all columns of the foreign-key constraint are nilified.

Nothing vs Restrict

references do
  reference :post, on_delete: :nothing
  # vs
  reference :post, on_delete: :restrict
end

The difference between :nothing and :restrict is subtle and, if you are unsure, choose :nothing (the default behavior). :restrict will immediately check the foreign-key constraint and prevent the update or deletion from happening, whereas :nothing allows the check to be deferred until later in the transaction. This allows for things like updating or deleting the destination row and then updating updating or deleting the reference (as long as you are in a transaction). The reason that :nothing still ultimately prevents the update or deletion is because postgres enforces foreign key referential integrity.