Fix cascade issue for GracePeriod (#775)

* Fix cascade issue for GracePeriod

* Rebase on HEAD

* Make GracePeriod immutable

* Add javadoc and use nullToEmptyImmutableCopy

core/src/main/java/google/registry/model/domain/DomainBase.java

@@ -14,7 +14,6 @@
 
 package google.registry.model.domain;
 
-
 import com.googlecode.objectify.Key;
 import google.registry.model.EppResource;
 import google.registry.model.EppResource.ForeignKeyedEppResource;
@@ -82,12 +81,26 @@ public class DomainBase extends DomainContent
     return super.nsHosts;
   }
 
+  /**
+   * Returns the set of {@link GracePeriod} associated with the domain.
+   *
+   * <p>This is the getter method specific for Hibernate to access the field so it is set to
+   * private. The caller can use the public {@link #getGracePeriods()} to get the grace periods.
+   *
+   * <p>Note that we need to set `insertable = false, updatable = false` for @JoinColumn, otherwise
+   * Hibernate would try to set the foreign key to null(through an UPDATE TABLE sql) instead of
+   * deleting the whole entry from the table when the {@link GracePeriod} is removed from the set.
+   */
   @Access(AccessType.PROPERTY)
   @OneToMany(
       cascade = {CascadeType.ALL},
       fetch = FetchType.EAGER,
       orphanRemoval = true)
-  @JoinColumn(name = "domainRepoId", referencedColumnName = "repoId")
+  @JoinColumn(
+      name = "domainRepoId",
+      referencedColumnName = "repoId",
+      insertable = false,
+      updatable = false)
   @SuppressWarnings("UnusedMethod")
   private Set<GracePeriod> getInternalGracePeriods() {
     return gracePeriods;

core/src/main/java/google/registry/model/domain/DomainContent.java

@@ -280,12 +280,10 @@ public class DomainContent extends EppResource
     // object will have a null hashcode so that it can get a recalculated hashcode
     // when its hashCode() is invoked.
     // TODO(b/162739503): Remove this after fully migrating to Cloud SQL.
-    if (gracePeriods != null) {
-      gracePeriods =
-          gracePeriods.stream()
-              .map(gracePeriod -> gracePeriod.cloneWithDomainRepoId(getRepoId()))
-              .collect(toImmutableSet());
-    }
+    gracePeriods =
+        nullToEmptyImmutableCopy(gracePeriods).stream()
+            .map(gracePeriod -> gracePeriod.cloneWithDomainRepoId(getRepoId()))
+            .collect(toImmutableSet());
   }
 
   @PostLoad
@@ -698,7 +696,13 @@ public class DomainContent extends EppResource
       }
       checkArgumentNotNull(instance.getRegistrant(), "Missing registrant");
       instance.tld = getTldFromDomainName(instance.fullyQualifiedDomainName);
-      return super.build();
+
+      T newDomain = super.build();
+      // Hibernate throws exception if gracePeriods is null because we enabled all cascadable
+      // operations and orphan removal.
+      newDomain.gracePeriods =
+          newDomain.gracePeriods == null ? ImmutableSet.of() : newDomain.gracePeriods;
+      return newDomain;
     }
 
     public B setDomainName(String domainName) {