Foreign Keys

Define relational constraints between custom tables using foreign keys.

A foreign key is a database-level constraint that links a column in one table to the primary key of another table. Foreign keys enforce referential integrity: you cannot create a record in the child table that references a non-existent record in the parent table, and you can control what happens when a parent record is deleted or updated.

Foreign keys are configured in Step 4 of the table wizard.

Creating a foreign key

1. Open the table wizard and navigate to Step 4 — Foreign Keys.

2. Click Add foreign key.

3. Fill in the constraint settings:

Field	Description
Constraint name	Unique identifier for this FK constraint (e.g. fk_movies_director).
Local column	The column in this table that holds the reference (e.g. director_id).
Reference table	The parent table (e.g. directors).
Reference column	The column in the parent table being referenced (usually id).
On delete	Action when the parent record is deleted (see actions below).
On update	Action when the parent key value is updated.

Referential actions

Action	Description
CASCADE	Automatically delete or update the child rows when the parent row is deleted/updated.
SET NULL	Set the foreign key column to NULL when the parent row is deleted/updated. Requires the column to be nullable.
RESTRICT	Prevent deletion/update of the parent row while child rows still reference it.
NO ACTION	Same as RESTRICT in MySQL (checked at the end of the statement).

(SET DEFAULT is not offered — InnoDB parses but ignores it.)

Example — Movies and Directors

A movies table references a directors table:

Field	Value
Constraint name	fk_movies_director_id
Local column	director_id
Reference table	directors
Reference column	id
On delete	SET NULL
On update	CASCADE

Step 4 — Foreign keys, showing the fk_movies_director_id constraint.

This means:

• A movie's director_id must match a valid id in directors.

• If a director is deleted, all their movies have director_id set to NULL (the movie is preserved but orphaned).

• If a director's id changes, the director_id in all related movies is updated automatically.

Deleting a foreign key

Click Delete next to the constraint in Step 4. The constraint is dropped from the database the next time the schema is synced.

Foreign key constraints only work with tables using the InnoDB storage engine. ACPT creates all custom tables as InnoDB by default.

See also

• Relational fields — for the UI-level relationship experience (linking records across tables via the admin form)