Remove unintended @ReadOnly from GormService

[codeconsole]

When I originally created GormService, the purpose was to provide CRUD operations implemented using GORM. It was modeled after RestfulController used by the scaffolding plugin. The intent was to have a RestfulServiceController that used a service layer instead of direct datastore access. I mistakenly added @ReadOnly. @ReadOnly should not be there because GORM get does not happen in a transaction so GormService get should not either.

Problem

GormService is annotated @ReadOnly at class level, so the transactional AST transform wraps get/list/count in a GrailsTransactionTemplate. With the default REQUIRED propagation, a read taken outside an existing transaction becomes the outermost transaction — and committing it flushes the session:

// DatastoreTransactionManager.doCommit
if (!status.isReadOnly()) {
    if (session != null) { ... session.flush(); }   // skipped when read-only
}
transaction.commit();                               // ...but this flushes anyway

// MongoTransaction.commit()
session.flush();
commitWithRetry();

So a read can write. @ReadOnly suppresses the transaction manager's own flush, but not the one inside commit().

That becomes a hang when such a read runs during a flush. A referential check in a validator is the ordinary case:

static constraints = {
    principalId validator: { String val -> Principal.get(val) != null ?: 'principal.missing' }
}

If Principal.get(...) reaches GormService, the commit of its read-only transaction flushes the session, the flush re-validates the entity being saved, the validator reads again, and the cycle repeats until the stack is exhausted. It surfaces well away from the cause — as IllegalStateException: Transaction synchronization is not active thrown out of the commit unwind, with the StackOverflowError lost. beforeInsert/beforeUpdate hooks are exposed the same way.

Change

Drop the class-level @ReadOnly from GormService. The write methods keep their own @Transactional.

The annotation is redundant where scaffolded reads are actually served: RestfulServiceController already declares @ReadOnly at class level, so that path keeps its read-only boundary either way. The service annotation only takes effect when the service is called outside one — which is exactly where opening and committing a transaction is unwanted, and where callers reasonably expect get(id) to behave like the GORM static call it delegates to.

Tests

:grails-scaffolding:test plus check on :grails-test-examples-scaffolding, :grails-test-examples-scaffolding-fields, and :grails-test-examples-hibernate7-scaffolding-fields (integration tests included) all pass.

Related

#16214 aligns the behaviour underneath this. @ReadOnly suppresses the flush on Hibernate but not on the DatastoreTransactionManager path, where doCommit's if (!status.isReadOnly()) guard is defeated by transaction.commit() flushing unconditionally in both MongoTransaction and SessionOnlyTransaction.

The two are independent. This one removes a @ReadOnly that a scaffold service should not carry regardless of what read-only ends up meaning; #16214 makes read-only mean the same thing on both paths. Either can land without the other.

(Minor, noticed while tracing it: the // Just set to NEVER in case of a new Session for this transaction. comment in doBegin is inherited from Spring's HibernateTransactionManager, which sets Hibernate's own FlushMode.MANUAL. jakarta.persistence.FlushModeType offers only AUTO and COMMIT, so the code is already as strict as the enum allows and the comment is what is stale. #16214 corrects it.)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.1155%. Comparing base (e40cb27) to head (608b8ea).

Additional details and impacted files

@@                Coverage Diff                 @@
##                8.0.x     #16212        +/-   ##
==================================================
- Coverage     54.1238%   54.1155%   -0.0084%     
+ Complexity      20307      20302         -5     
==================================================
  Files            2107       2107                
  Lines          101144     101143         -1     
  Branches        17921      17921                
==================================================
- Hits            54743      54734         -9     
- Misses          38595      38602         +7     
- Partials         7806       7807         +1     

Files with missing lines	Coverage Δ
...roovy/grails/plugin/scaffolding/GormService.groovy	0.0000% <ø> (ø)

... and 2 files with indirect coverage changes

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[testlens-app]

✅ All tests passed ✅

🏷️ Commit: 608b8ea
▶️ Tests: 69321 executed
⚪️ Checks: 83/83 completed

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