feat: impl many to many deletion strategy

[Sammster10]

No description provided.

[Copilot]

Pull request overview

This PR adds first-class deletion strategy support for @ManyToMany relationships by configuring join-table foreign keys appropriately and generating database triggers to enforce @Delete behavior consistently across PostgreSQL and H2, with accompanying documentation and test coverage.

Changes:

• Implement many-to-many deletion behavior via new SQL trigger generation (PostgreSQL PL/pgSQL + H2 Trigger class) driven by @Delete(DeleteStrategy).
• Update many-to-many foreign key ON DELETE behavior to align with CASCADE/SET_NULL/NO_ACTION semantics.
• Add comprehensive tests validating join cleanup, child deletion behavior, composite links, and operation without foreign keys; update docs/javadocs to reflect semantics.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
README.md	Documents updated many-to-many deletion semantics for @Delete.
core/src/test/java/net/staticstudios/data/mock/user/MockUser.java	Removes now-obsolete TODO comment about unimplemented many-to-many delete strategy.
core/src/test/java/net/staticstudios/data/DeletionTest.java	Adds extensive tests for many-to-many deletion strategies, triggers, FKs, and composite links.
core/src/main/java/net/staticstudios/data/parse/SQLManyToManyDeleteStrategyTrigger.java	Introduces SQL trigger DDL generation for many-to-many delete strategy behavior.
core/src/main/java/net/staticstudios/data/parse/SQLBuilder.java	Wires many-to-many delete strategy into FK ON DELETE rules and trigger creation.
core/src/main/java/net/staticstudios/data/impl/h2/trigger/H2ManyToManyDeleteStrategyTrigger.java	Adds H2 trigger implementation to enforce many-to-many deletion behavior.
annotations/src/main/java/net/staticstudios/data/ManyToMany.java	Clarifies that delete strategies are still applied via triggers when fkey=false.
annotations/src/main/java/net/staticstudios/data/DeleteStrategy.java	Updates enum documentation to reflect many-to-many behavior for each strategy.
annotations/src/main/java/net/staticstudios/data/Delete.java	Adds/clarifies javadoc for @Delete.

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