#3529 - Fix for M2M property is empty in preDelete of BeanPersistAdapter (#3830)

Co-authored-by: robin.bygrave <robin.bygrave@eroad.com>

ebean-core/src/main/java/io/ebeaninternal/server/core/PersistRequestBean.java

@@ -132,6 +132,13 @@ public final class PersistRequestBean<T> extends PersistRequest implements BeanP
    * Cascade to children must be suppressed to avoid FK violations.
    */
   private boolean insertConflictSkipped;
+  /**
+   * Set true once controller.preDelete() has been invoked so that it is
+   * only ever fired once (as it is fired early, prior to cascading the
+   * delete to children/many's rather than as part of executing the delete).
+   */
+  private boolean preDeleteCalled;
+  private boolean preDeleteResult = true;
 
   public PersistRequestBean(SpiEbeanServer server, T bean, Object parentBean, BeanManager<T> mgr, SpiTransaction t,
                             PersistExecute persistExecute, PersistRequest.Type type, int flags) {
@@ -1276,14 +1283,29 @@ public final class PersistRequestBean<T> extends PersistRequest implements BeanP
   }
 
   private int executeDelete() {
-    setTenantId();
-    if (controller == null || controller.preDelete(this)) {
+    if (controllerPreDelete()) {
       return beanManager.getBeanPersister().delete(this);
     }
     // delete handled by the BeanController so return 0
     return 0;
   }
 
+  /**
+   * Invoke controller.preDelete() if not already invoked.
+   * <p>
+   * This is called prior to cascading the delete to children (assoc many's /
+   * many-to-many intersection rows) so that the persist controller can still
+   * see those collections/relationships as they were before the cascade delete.
+   */
+  public boolean controllerPreDelete() {
+    if (!preDeleteCalled) {
+      preDeleteCalled = true;
+      setTenantId();
+      preDeleteResult = controller == null || controller.preDelete(this);
+    }
+    return preDeleteResult;
+  }
+
   /**
    * Persist to the document store now (via buffer, not post commit).
    */

ebean-core/src/main/java/io/ebeaninternal/server/persist/DefaultPersister.java

@@ -907,6 +907,11 @@ public final class DefaultPersister implements Persister {
    * </p>
    */
   private int delete(PersistRequestBean<?> request) {
+    // fire preDelete now, before cascading to children/many's so that the
+    // BeanPersistController/Adapter still sees the bean's collections and
+    // relationships as they are prior to the cascade delete
+    request.controllerPreDelete();
+
     DeleteUnloadedForeignKeys unloadedForeignKeys = null;
     if (request.isPersistCascade()) {
       // delete children first ... register the

ebean-test/src/test/java/io/ebean/xtest/event/BeanPersistControllerTest.java

@@ -9,6 +9,9 @@ import io.ebean.event.BeanPersistRequest;
 import org.junit.jupiter.api.Test;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import org.tests.model.m2m.MnyA;
+import org.tests.model.m2m.MnyB;
+import org.tests.model.m2m.MnyC;
 import org.tests.model.m2m.MnyTopic;
 import org.tests.model.basic.EBasicVer;
 import org.tests.model.basic.UTDetail;
@@ -166,6 +169,56 @@ public class BeanPersistControllerTest {
     db.shutdown();
   }
 
+  @Test
+  public void preDelete_seesManyToManyCollection_beforeCascadeDelete() {
+    List<List<MnyC>> capturedCs = new ArrayList<>();
+    BeanPersistAdapter mnyBAdapter = new BeanPersistAdapter() {
+      @Override
+      public boolean isRegisterFor(Class<?> cls) {
+        return MnyB.class.isAssignableFrom(cls);
+      }
+
+      @Override
+      public boolean preDelete(BeanPersistRequest<?> request) {
+        // the M2M collection should still be intact here, before the
+        // intersection table rows are cascade deleted
+        capturedCs.add(new ArrayList<>(((MnyB) request.bean()).getCs()));
+        return true;
+      }
+    };
+
+    DatabaseBuilder config = Database.builder();
+    config.setName("h2ebasicver");
+    config.setRegister(false);
+    config.setDefaultServer(false);
+    config.loadFromProperties();
+    config.setDdlGenerate(true);
+    config.setDdlRun(true);
+    config.setDdlExtra(false);
+    config.addClass(MnyA.class);
+    config.addClass(MnyB.class);
+    config.addClass(MnyC.class);
+    config.add(mnyBAdapter);
+    Database db = config.build();
+
+    try {
+      MnyB mnyB = new MnyB();
+      MnyC mnyC = new MnyC();
+      mnyB.setCs(new ArrayList<>());
+      mnyB.getCs().add(mnyC);
+      db.save(mnyC);
+      db.save(mnyB);
+
+      MnyB mnyBFromDB = db.find(MnyB.class, mnyB.getId());
+      db.delete(mnyBFromDB);
+
+      assertThat(capturedCs).hasSize(1);
+      assertThat(capturedCs.get(0)).extracting("id").containsExactly(mnyC.getId());
+    } finally {
+      db.shutdown();
+    }
+  }
+
   private Database createDatabase(PersistAdapter persistAdapter) {
     DatabaseBuilder config = Database.builder();
     config.setName("h2ebasicver");