Support changing of transaction's isolation level via aspect (#126)

Authored-by: Alexander Trunin <alextrunin@nebius.com>

Author: jorki02

aspect/src/main/java/tech/ydb/yoj/aspect/tx/YojTransactionAspect.java

@@ -48,12 +48,28 @@ private Object doInTransaction(ProceedingJoinPoint pjp, YojTransactional transac
             if (transactional.maxRetries() != YojTransactional.UNDEFINED) {
                 localTx = tx.withMaxRetries(transactional.maxRetries());
             }
-            return transactional.readOnly() ? localTx.readOnly().run(() -> safeCall(pjp)) : localTx.tx(() -> safeCall(pjp));
+
+            validateIsolationLevel(transactional);
+
+            if (transactional.readOnly()) {
+                return localTx
+                    .readOnly()
+                    .withStatementIsolationLevel(transactional.isolation())
+                    .run(() -> safeCall(pjp));
+            } else {
+                return localTx.tx(() -> safeCall(pjp));
+            }
         } catch (CallRetryableException | CallException e) {
             throw e.getCause();
         }
     }
 
+    private void validateIsolationLevel(YojTransactional transactional) {
+        if (transactional.isolation().isReadWrite() && transactional.readOnly()) {
+            throw new IllegalStateException("Unsupported isolation level for read-only transaction: " + transactional.isolation());
+        }
+    }
+
     private static String getSimpleMethod(Signature signature) {
         return signature.getDeclaringType().getSimpleName() + "." + signature.getName();
     }

aspect/src/main/java/tech/ydb/yoj/aspect/tx/YojTransactional.java

@@ -1,5 +1,7 @@
 package tech.ydb.yoj.aspect.tx;
 
+import tech.ydb.yoj.repository.db.IsolationLevel;
+
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Inherited;
 import java.lang.annotation.Retention;
@@ -23,6 +25,17 @@
      */
     boolean readOnly() default false;
 
+    /**
+     * Indicates isolation level of transaction.
+     * If transaction marked as read only, then following isolation levels are supported:
+     * ONLINE_CONSISTENT_READ_ONLY
+     * ONLINE_INCONSISTENT_READ_ONLY
+     * STALE_CONSISTENT_READ_ONLY
+     * SNAPSHOT
+     * If transaction marked as not read only, isolation level is ignored.
+     */
+    IsolationLevel isolation() default IsolationLevel.ONLINE_CONSISTENT_READ_ONLY;
+
     /**
      * Set transaction name otherwise method name will be used as transaction name
      */