[EDM] Refactor Extension Entity for Parent-Child Entity Inheritance

[ThuF]

Goal

Introduce a standardized Extension Entity pattern to allow common entities to be extended efficiently, supporting multiple inheritance, internationalization, and performant queries.

Scope

• Enable Extension Entities to extend common entities, e.g.:
  • Address → CustomerAddress, SupplierAddress, ManufacturerAddress, EmployeeAddress
  • Contact → CustomerContact, SupplierContact, etc.
• CRUD operations (get, save, update, delete) should use the parent repository for single record.
• list / filter operations should generate custom SQL/HSQL/store queries for performance.
• Support multiple inheritance chains, e.g.:
  • ParentA → ChildB → ChildC → ChildD
• Handle internationalization with language tables where relevant.

Description

Currently, there is no standardized way to extend entities in Eclipse Dirigible EDM.
This issue introduces a parent-child pattern for extension entities, inspired by Mendix’s Parent → Child model:

• Parent entity: contains all common properties, manages persistence.
• Child entity: contains only child-specific properties and has reference to parent.
• CRUD operations (get, save, update, delete) are handled through parent repositories to ensure consistency.
• Listing and filtering operations generate optimized queries capable of handling:
  • Multiple inheritance chains
  • Internationalized data via language tables

This refactor improves modularity, reduces duplication, and enables consistent handling of shared properties across entities like Address and Contact.

Acceptance Criteria

• Extension entities can inherit from parent entities (e.g., Address → CustomerAddress).
• Parent repository handles CRUD operations for children.
• Custom queries generated for list/filter operations are performant.
• Multiple inheritance chains supported.
• Internationalization supported via language tables.
• Templates are updated to support the new behaviour.