Implement CASCADE behavior enforcement for FOREIGN KEY constraints

[Copilot]

Description

AlaSQL parsed CASCADE syntax but did not enforce it. Deleting or updating parent rows left child rows orphaned.

Changes

Parser (alasqlparser.jison)

• Added grammar rules for ON DELETE/UPDATE actions: CASCADE, SET NULL, SET DEFAULT, RESTRICT, NO ACTION
• Handle CASCADE/RESTRICT as non-reserved literals with runtime validation

Metadata Storage (23table.js, 60createtable.js)

• Store foreign key relationships in table.foreignKeys[] with action metadata
• Capture both column-level and table-level foreign key constraints

DELETE Handler (72delete.js)

• Recursive applyCascadeDeletes() helper for multi-level cascades
• CASCADE: Delete matching child rows (and grandchildren)
• SET NULL: Set foreign key columns to NULL (validates NOT NULL constraints)
• SET DEFAULT: Set to default values (validates NOT NULL without defaults)
• RESTRICT/NO ACTION: Throw error if child rows exist
• Use row references instead of indices to avoid invalidation during recursion

UPDATE Handler (74update.js)

• Pre-check RESTRICT before modifying data
• CASCADE: Update child foreign keys when parent primary key changes
• SET NULL/SET DEFAULT: Same validation as DELETE
• Only triggers when primary key columns are modified

Example

alasql('CREATE TABLE parent (id INT PRIMARY KEY)');
alasql('CREATE TABLE child (id INT, parent_id INT, ' +
       'FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE CASCADE)');

alasql('INSERT INTO parent VALUES (1), (2)');
alasql('INSERT INTO child VALUES (10, 1), (11, 1), (20, 2)');

alasql('DELETE FROM parent WHERE id = 1');
// child rows 10 and 11 automatically deleted
alasql('SELECT * FROM child'); // Returns [{id: 20, parent_id: 2}]

Testing

Added test/test897.js with 12 test cases covering all CASCADE actions, recursive cascades, and constraint violations.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Implement CASCADE behavior enforcement for FOREIGN KEY constraints</issue_title>
<issue_description>AlaSQL currently parses CASCADE syntax but does not enforce the behavior. When a parent row is deleted or updated, child rows with ON DELETE CASCADE or ON UPDATE CASCADE are not automatically affected.

What needs to be implemented

ON DELETE actions:

• CASCADE: When a row in the parent table is deleted, automatically delete all rows in child tables that reference it
• SET NULL: Set foreign key columns to NULL in child tables when parent is deleted
• SET DEFAULT: Set foreign key columns to their default value when parent is deleted
• RESTRICT: Prevent deletion of parent row if child rows exist
• NO ACTION: Same as RESTRICT per SQL-99 standard

ON UPDATE actions:

• CASCADE: When parent key is updated, update matching foreign keys in child tables
• SET NULL: Set foreign key to NULL when parent key is updated
• SET DEFAULT: Set foreign key to default when parent key is updated
• RESTRICT: Prevent update of parent key if child rows exist
• NO ACTION: Same as RESTRICT per SQL-99 standard

Implementation areas

• Modify DELETE statement handler (src/74delete.js) to check for child tables and apply CASCADE actions
• Modify UPDATE statement handler (src/74update.js) to check for child tables and apply CASCADE actions
• Store foreign key metadata including ondelete/onupdate actions in table definition during CREATE TABLE
• Add validation for RESTRICT actions before allowing delete/update
• Handle circular dependencies and prevent infinite loops

Related

• Fixes parsing: CASCADE not supported (sqlite)  #897
• Parser support added in: PR Add parser support for ON DELETE and ON UPDATE CASCADE in REFERENCES #2311
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Implement CASCADE behavior enforcement for FOREIGN KEY constraints #2336

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.