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
• Optimized: Only call table.delete() to update indices when primary key or unique keys exist

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.

Test Quality Improvements:

• All assertions use assert.deepEqual() for complete object comparison
• Unique table names for tests to prevent schema conflicts
• DROP TABLE IF EXISTS at test start for clean state
• afterEach cleanup hook to ensure proper cleanup between tests

Original prompt

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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

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[mathiasrw]

Looks like a lot of code. Are you sure this is the best way to solve this problem?

[Copilot]

This is the minimum code needed for SQL-standard CASCADE behavior. The ~90 lines handle all 5 CASCADE actions (CASCADE, SET NULL, SET DEFAULT, RESTRICT, NO ACTION) with recursive support for grandchild rows and NOT NULL validation. The core logic is in the applyCascadeDeletes helper function which is reused for both WHERE and non-WHERE deletes to avoid duplication.

Commit b53bc38

[mathiasrw]

Can we do this only if there are indexes?

[Copilot]

Good catch! Optimized to only call table.delete() when there are primary key or unique key indices that need updating. Added condition: if (table.pk || (table.uk && table.uk.length)) before the index update loop.

Commit b53bc38

[mathiasrw]

This seems like way too much code for this problem. Are you sure this is the best way to do it?

[Copilot]

The ~200 lines in UPDATE handle all CASCADE actions for primary key changes, including pre-validation for RESTRICT, NOT NULL constraint checking, and tracking which columns are being updated to avoid unnecessary cascade operations. This is the minimum needed to properly implement SQL-99 CASCADE standard for UPDATE operations.

Commit b53bc38

[mathiasrw]

Please make sure to assert the whole response object with the expected output.

[Copilot]

Updated all test assertions to use assert.deepEqual() for full object comparison instead of checking individual properties. This provides better test coverage and clearer failure messages. Also added unique table names and proper cleanup between tests.

Commit b53bc38