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<issue_title>Upgrade Roadiz to Doctrine ORM 3.x</issue_title>
<issue_description># 🚀 Migration Plan: Upgrade Roadiz to Doctrine ORM 3.x

Context

Roadiz currently relies on Doctrine ORM 2.x, which has reached end-of-life. Doctrine ORM 3.x introduces significant internal refactoring, removal of deprecated APIs, and ecosystem alignment (DoctrineBundle 3, DBAL 3+, etc.).

This issue tracks the full migration of Roadiz to Doctrine ORM 3.6.x (stable minor target), ensuring:

• Forward compatibility
• Removal of deprecated APIs
• Improved performance and maintainability
• Alignment with the current Symfony/Doctrine ecosystem

🎯 Target Stack

🧭 Migration Strategy (Phased Approach)

We will not attempt a big-bang upgrade. Migration will be done in controlled phases.

Phase 1 — Stabilize on Latest ORM 2.x (Pre-Upgrade Cleanup)

Goal

Eliminate all deprecations under ORM 2.21 before moving to 3.x.

Tasks

• Upgrade to doctrine/orm:^2.21
• Upgrade to doctrine/dbal:^3
• Enable deprecation reporting in CI
• Fix all deprecations
• Ensure full test suite passes
• Validate schema: bin/console doctrine:schema:validate

Why?

Doctrine officially recommends upgrading to the latest 2.x and clearing deprecations before jumping to 3.x.

Phase 2 — DoctrineBundle 3 Upgrade

DoctrineBundle 3 removed legacy support (annotations, YAML mapping, legacy config options).

Tasks

• Upgrade to doctrine/doctrine-bundle:^3
• Update Symfony config to remove deprecated options
• Ensure cache pools are properly configured
• Remove any legacy Doctrine\ORM\Tools\Setup usage
• Verify event listeners and subscribers still register properly
• Ensure compatibility with current Symfony version

Phase 3 — Mapping Migration (Critical)

DoctrineBundle 3 removes support for:

• ❌ Annotations
• ❌ YAML mapping

If Roadiz uses annotations:

@ORM\Entity

They must be converted to PHP Attributes:

#[ORM\Entity]

If YAML mappings exist:

They must be converted to:

• PHP Attributes (preferred)
• OR XML mapping

Tasks

• Scan repository for @ORM\
• Scan for .orm.yml files
• Convert annotations to PHP attributes
• Remove YAML mapping definitions
• Validate metadata mapping with doctrine:schema:validate
• Clear metadata and proxy cache

Phase 4 — Removed APIs & Breaking Changes (ORM 3)

This is the most critical phase.

1️⃣ EntityManager::merge() Removed

Find

->merge(

Required Refactor

Replace merge usage with explicit load + patch pattern:

$entity = $repository->find($id);
$entity->setFoo($dto->foo);
$em->flush();

No automatic graph reattachment exists in ORM 3.

2️⃣ Cascade "merge" Removed

Find

cascade={"merge"}

Action

Remove merge from cascade definitions.

Allowed cascade options:

• persist
• remove
• refresh
• detach

3️⃣ Flush Behavior Review

Audit usage of:

$em->flush($entity);

Ensure no reliance on legacy partial flush semantics.

Prefer full flush unless explicitly safe.

4️⃣ Proxy & Lazy Loading Changes

ORM 3 introduces internal improvements and optional Native Lazy Objects.

Tasks

• Verify lazy loading works in Twig templates
• Verify serialization (API responses)
• Test backoffice entity forms
• Benchmark homepage and node listing performance
• Detect potential N+1 regressions

Phase 5 — Query & Hydration Review

Audit advanced ORM usage:

• ResultSetMapping
• Custom hydrators
• iterate()
• toIterable()
• Scalar hydration
• DQL PARTIAL objects
• Custom query hints

Tasks

• Identify custom hydrators
• Run regression tests on heavy queries
• Validate pagination logic
• Validate DQL compatibility

Phase 6 — Migrations & Tooling

• Verify doctrine/migrations compatibility
• Test schema diff generation
• Test database migrations execution
• Validate fixtures loading
• Validate custom Roadiz CLI commands
• Ensure test database setup works correctly

🔎 Repository Audit Commands

Run these before starting Phase 4:

rg -n "->merge\s*\(" .
rg -n "cascade\s*=\s*\{[^}]*merge|cascade:\s*\[[^\]]*merge|cascade:\s*\{[^}]*merge" .
rg -n "@ORM\\\\" .
rg -n "type:\s*yml|\\.orm\\.yml" .
rg -n "Doctrine\\\\Common\\\\Persistence" .
rg -n "Doctrine\\\\ORM\\\\Tools\\\\Setup" .

Attach results to this issue for tracking.

🧪 Testing Requirements

Minimum validation checklist before merge:

• All PHPUnit tests pass
• No deprecations remain
• Admin CRU...