Add columns for TransferData in Domain and Contact (#577)

* Add columns for TransferData in Domain and Contact

* Rename flyway file and foreign key

* Rebase on master and address comment

* Compileable commit

* Fix unit test

* Refactor TransferServerApproveEntity

* Use tm().delete(vkeys)

* Rename transfer_period fields

* Rename client_id to registrar_id

* Rebase on master

* Resolve comment

* Rebase on master

core/src/main/java/google/registry/flows/contact/ContactTransferApproveFlow.java

@@ -97,7 +97,7 @@ public final class ContactTransferApproveFlow implements TransactionalFlow {
     ofy().save().<Object>entities(newContact, historyEntry, gainingPollMessage);
     // Delete the billing event and poll messages that were written in case the transfer would have
     // been implicitly server approved.
-    ofy().delete().keys(existingContact.getTransferData().getServerApproveEntities());
+    tm().delete(existingContact.getTransferData().getServerApproveEntities());
     return responseBuilder
         .setResData(createTransferResponse(targetId, newContact.getTransferData()))
         .build();

core/src/main/java/google/registry/flows/contact/ContactTransferCancelFlow.java

@@ -93,7 +93,7 @@ public final class ContactTransferCancelFlow implements TransactionalFlow {
     ofy().save().<Object>entities(newContact, historyEntry, losingPollMessage);
     // Delete the billing event and poll messages that were written in case the transfer would have
     // been implicitly server approved.
-    ofy().delete().keys(existingContact.getTransferData().getServerApproveEntities());
+    tm().delete(existingContact.getTransferData().getServerApproveEntities());
     return responseBuilder
         .setResData(createTransferResponse(targetId, newContact.getTransferData()))
         .build();

core/src/main/java/google/registry/flows/contact/ContactTransferRejectFlow.java

@@ -90,7 +90,7 @@ public final class ContactTransferRejectFlow implements TransactionalFlow {
     ofy().save().<Object>entities(newContact, historyEntry, gainingPollMessage);
     // Delete the billing event and poll messages that were written in case the transfer would have
     // been implicitly server approved.
-    ofy().delete().keys(existingContact.getTransferData().getServerApproveEntities());
+    tm().delete(existingContact.getTransferData().getServerApproveEntities());
     return responseBuilder
         .setResData(createTransferResponse(targetId, newContact.getTransferData()))
         .build();

core/src/main/java/google/registry/flows/contact/ContactTransferRequestFlow.java

@@ -126,13 +126,15 @@ public final class ContactTransferRequestFlow implements TransactionalFlow {
     // If the transfer is server approved, this message will be sent to the gaining registrar. */
     PollMessage serverApproveGainingPollMessage =
         createGainingTransferPollMessage(targetId, serverApproveTransferData, historyEntry);
-    TransferData pendingTransferData = serverApproveTransferData.asBuilder()
-        .setTransferStatus(TransferStatus.PENDING)
-        .setServerApproveEntities(
-            ImmutableSet.of(
-                Key.create(serverApproveGainingPollMessage),
-                Key.create(serverApproveLosingPollMessage)))
-        .build();
+    TransferData pendingTransferData =
+        serverApproveTransferData
+            .asBuilder()
+            .setTransferStatus(TransferStatus.PENDING)
+            .setServerApproveEntities(
+                ImmutableSet.of(
+                    serverApproveGainingPollMessage.createVKey(),
+                    serverApproveLosingPollMessage.createVKey()))
+            .build();
     // When a transfer is requested, a poll message is created to notify the losing registrar.
     PollMessage requestPollMessage =
         createLosingTransferPollMessage(targetId, pendingTransferData, historyEntry).asBuilder()

core/src/main/java/google/registry/flows/domain/DomainTransferApproveFlow.java

@@ -214,7 +214,7 @@ public final class DomainTransferApproveFlow implements TransactionalFlow {
     ofy().save().entities(entitiesToSave.build());
     // Delete the billing event and poll messages that were written in case the transfer would have
     // been implicitly server approved.
-    ofy().delete().keys(existingDomain.getTransferData().getServerApproveEntities());
+    tm().delete(existingDomain.getTransferData().getServerApproveEntities());
     return responseBuilder
         .setResData(createTransferResponse(
             targetId, newDomain.getTransferData(), newDomain.getRegistrationExpirationTime()))

core/src/main/java/google/registry/flows/domain/DomainTransferCancelFlow.java

@@ -110,7 +110,7 @@ public final class DomainTransferCancelFlow implements TransactionalFlow {
     updateAutorenewRecurrenceEndTime(existingDomain, END_OF_TIME);
     // Delete the billing event and poll messages that were written in case the transfer would have
     // been implicitly server approved.
-    ofy().delete().keys(existingDomain.getTransferData().getServerApproveEntities());
+    tm().delete(existingDomain.getTransferData().getServerApproveEntities());
     return responseBuilder
         .setResData(createTransferResponse(targetId, newDomain.getTransferData(), null))
         .build();

core/src/main/java/google/registry/flows/domain/DomainTransferRejectFlow.java

@@ -112,7 +112,7 @@ public final class DomainTransferRejectFlow implements TransactionalFlow {
     updateAutorenewRecurrenceEndTime(existingDomain, END_OF_TIME);
     // Delete the billing event and poll messages that were written in case the transfer would have
     // been implicitly server approved.
-    ofy().delete().keys(existingDomain.getTransferData().getServerApproveEntities());
+    tm().delete(existingDomain.getTransferData().getServerApproveEntities());
     return responseBuilder
         .setResData(createTransferResponse(targetId, newDomain.getTransferData(), null))
         .build();

core/src/main/java/google/registry/flows/domain/DomainTransferUtils.java

@@ -20,7 +20,6 @@ import static google.registry.util.DateTimeUtils.END_OF_TIME;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
-import com.googlecode.objectify.Key;
 import google.registry.model.billing.BillingEvent;
 import google.registry.model.billing.BillingEvent.Flag;
 import google.registry.model.billing.BillingEvent.Reason;
@@ -37,6 +36,7 @@ import google.registry.model.transfer.TransferData;
 import google.registry.model.transfer.TransferData.TransferServerApproveEntity;
 import google.registry.model.transfer.TransferResponse.DomainTransferResponse;
 import google.registry.model.transfer.TransferStatus;
+import google.registry.persistence.VKey;
 import java.util.Optional;
 import javax.annotation.Nullable;
 import org.joda.money.Money;
@@ -52,37 +52,34 @@ public final class DomainTransferUtils {
       TransferData.Builder transferDataBuilder,
       ImmutableSet<TransferServerApproveEntity> serverApproveEntities,
       Period transferPeriod) {
-    ImmutableSet.Builder<Key<? extends TransferServerApproveEntity>> serverApproveEntityKeys =
+    ImmutableSet.Builder<VKey<? extends TransferServerApproveEntity>> serverApproveEntityKeys =
         new ImmutableSet.Builder<>();
     for (TransferServerApproveEntity entity : serverApproveEntities) {
-      serverApproveEntityKeys.add(Key.create(entity));
+      serverApproveEntityKeys.add(entity.createVKey());
     }
     if (transferPeriod.getValue() != 0) {
       // Unless superuser sets period to 0, add a transfer billing event.
       transferDataBuilder.setServerApproveBillingEvent(
-          Key.create(
-              serverApproveEntities
-                  .stream()
-                  .filter(BillingEvent.OneTime.class::isInstance)
-                  .map(BillingEvent.OneTime.class::cast)
-                  .collect(onlyElement())));
+          serverApproveEntities.stream()
+              .filter(BillingEvent.OneTime.class::isInstance)
+              .map(BillingEvent.OneTime.class::cast)
+              .collect(onlyElement())
+              .createVKey());
     }
     return transferDataBuilder
         .setTransferStatus(TransferStatus.PENDING)
         .setServerApproveAutorenewEvent(
-            Key.create(
-                serverApproveEntities
-                    .stream()
-                    .filter(BillingEvent.Recurring.class::isInstance)
-                    .map(BillingEvent.Recurring.class::cast)
-                    .collect(onlyElement())))
+            serverApproveEntities.stream()
+                .filter(BillingEvent.Recurring.class::isInstance)
+                .map(BillingEvent.Recurring.class::cast)
+                .collect(onlyElement())
+                .createVKey())
         .setServerApproveAutorenewPollMessage(
-            Key.create(
-                serverApproveEntities
-                    .stream()
-                    .filter(PollMessage.Autorenew.class::isInstance)
-                    .map(PollMessage.Autorenew.class::cast)
-                    .collect(onlyElement())))
+            serverApproveEntities.stream()
+                .filter(PollMessage.Autorenew.class::isInstance)
+                .map(PollMessage.Autorenew.class::cast)
+                .collect(onlyElement())
+                .createVKey())
         .setServerApproveEntities(serverApproveEntityKeys.build())
         .setTransferPeriod(transferPeriod)
         .build();

core/src/main/java/google/registry/model/ResourceTransferUtils.java

@@ -18,6 +18,7 @@ import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkState;
 import static google.registry.model.ofy.ObjectifyService.ofy;
+import static google.registry.persistence.transaction.TransactionManagerFactory.tm;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
@@ -114,7 +115,7 @@ public final class ResourceTransferUtils {
             R resource, R newResource, DateTime now, HistoryEntry historyEntry) {
     if (resource.getStatusValues().contains(StatusValue.PENDING_TRANSFER)) {
       TransferData oldTransferData = resource.getTransferData();
-      ofy().delete().keys(oldTransferData.getServerApproveEntities());
+      tm().delete(oldTransferData.getServerApproveEntities());
       ofy()
           .save()
           .entity(

core/src/main/java/google/registry/model/billing/BillingEvent.java

@@ -345,6 +345,7 @@ public abstract class BillingEvent extends ImmutableObject
       return Optional.ofNullable(allocationToken);
     }
 
+    @Override
     public VKey<OneTime> createVKey() {
       return VKey.createOfy(getClass(), Key.create(this));
     }
@@ -482,6 +483,7 @@ public abstract class BillingEvent extends ImmutableObject
       return recurrenceTimeOfYear;
     }
 
+    @Override
     public VKey<Recurring> createVKey() {
       return VKey.createOfy(getClass(), Key.create(this));
     }
@@ -603,6 +605,7 @@ public abstract class BillingEvent extends ImmutableObject
       return builder.build();
     }
 
+    @Override
     public VKey<Cancellation> createVKey() {
       return VKey.createOfy(getClass(), Key.create(this));
     }
@@ -682,6 +685,11 @@ public abstract class BillingEvent extends ImmutableObject
       return new Builder(clone(this));
     }
 
+    @Override
+    public VKey<Modification> createVKey() {
+      return VKey.createOfy(this.getClass(), Key.create(this));
+    }
+
     /**
      * Create a new Modification billing event which is a refund of the given OneTime billing event
      * and that is parented off the given HistoryEntry.

core/src/main/java/google/registry/model/contact/ContactResource.java

@@ -41,7 +41,6 @@ import javax.persistence.AttributeOverride;
 import javax.persistence.AttributeOverrides;
 import javax.persistence.Column;
 import javax.persistence.Embedded;
-import javax.persistence.Transient;
 import javax.xml.bind.annotation.XmlElement;
 import org.joda.time.DateTime;
 
@@ -171,8 +170,7 @@ public class ContactResource extends EppResource
   ContactAuthInfo authInfo;
 
   /** Data about any pending or past transfers on this contact. */
-  // TODO(b/153363295): Figure out how to persist transfer data
-  @Transient TransferData transferData;
+  TransferData transferData;
 
   /**
    * The time that this resource was last transferred.

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

@@ -253,7 +253,7 @@ public class DomainBase extends EppResource
   String smdId;
 
   /** Data about any pending or past transfers on this domain. */
-  @Transient TransferData transferData;
+  TransferData transferData;
 
   /**
    * The time that this resource was last transferred.
@@ -438,8 +438,14 @@ public class DomainBase extends EppResource
               .setRegistrationExpirationTime(expirationDate)
               // Set the speculatively-written new autorenew events as the domain's autorenew
               // events.
-              .setAutorenewBillingEvent(transferData.getServerApproveAutorenewEvent())
-              .setAutorenewPollMessage(transferData.getServerApproveAutorenewPollMessage());
+              .setAutorenewBillingEvent(
+                  transferData.getServerApproveAutorenewEvent() == null
+                      ? null
+                      : transferData.getServerApproveAutorenewEvent().getOfyKey())
+              .setAutorenewPollMessage(
+                  transferData.getServerApproveAutorenewPollMessage() == null
+                      ? null
+                      : transferData.getServerApproveAutorenewPollMessage().getOfyKey());
       if (transferData.getTransferPeriod().getValue() == 1) {
         // Set the grace period using a key to the prescheduled transfer billing event.  Not using
         // GracePeriod.forBillingEvent() here in order to avoid the actual Datastore fetch.
@@ -450,7 +456,9 @@ public class DomainBase extends EppResource
                     transferExpirationTime.plus(
                         Registry.get(getTld()).getTransferGracePeriodLength()),
                     transferData.getGainingClientId(),
-                    transferData.getServerApproveBillingEvent())));
+                    transferData.getServerApproveBillingEvent() == null
+                        ? null
+                        : transferData.getServerApproveBillingEvent().getOfyKey())));
       } else {
         // There won't be a billing event, so we don't need a grace period
         builder.setGracePeriods(ImmutableSet.of());

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

@@ -16,6 +16,8 @@ package google.registry.model.domain;
 
 import com.googlecode.objectify.annotation.Embed;
 import google.registry.model.ImmutableObject;
+import javax.persistence.EnumType;
+import javax.persistence.Enumerated;
 import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlEnumValue;
 import javax.xml.bind.annotation.XmlValue;
@@ -25,6 +27,7 @@ import javax.xml.bind.annotation.XmlValue;
 @javax.persistence.Embeddable
 public class Period extends ImmutableObject {
 
+  @Enumerated(EnumType.STRING)
   @XmlAttribute
   Unit unit;
 

core/src/main/java/google/registry/model/poll/PollMessage.java

@@ -43,6 +43,7 @@ import google.registry.model.transfer.TransferData.TransferServerApproveEntity;
 import google.registry.model.transfer.TransferResponse;
 import google.registry.model.transfer.TransferResponse.ContactTransferResponse;
 import google.registry.model.transfer.TransferResponse.DomainTransferResponse;
+import google.registry.persistence.VKey;
 import google.registry.persistence.WithLongVKey;
 import java.util.List;
 import java.util.Optional;
@@ -150,6 +151,9 @@ public abstract class PollMessage extends ImmutableObject
 
   public abstract ImmutableList<ResponseData> getResponseData();
 
+  @Override
+  public abstract VKey<? extends PollMessage> createVKey();
+
   /** Override Buildable.asBuilder() to give this method stronger typing. */
   @Override
   public abstract Builder<?, ?> asBuilder();
@@ -291,6 +295,11 @@ public abstract class PollMessage extends ImmutableObject
     @Column(name = "transfer_response_contact_id")
     String contactId;
 
+    @Override
+    public VKey<OneTime> createVKey() {
+      return VKey.createOfy(this.getClass(), Key.create(this));
+    }
+
     @Override
     public Builder asBuilder() {
       return new Builder(clone(this));
@@ -387,6 +396,11 @@ public abstract class PollMessage extends ImmutableObject
       return autorenewEndTime;
     }
 
+    @Override
+    public VKey<Autorenew> createVKey() {
+      return VKey.createOfy(this.getClass(), Key.create(this));
+    }
+
     @Override
     public ImmutableList<ResponseData> getResponseData() {
       // Note that the event time is when the auto-renew occured, so the expiration time in the

core/src/main/java/google/registry/model/transfer/BaseTransferObject.java

@@ -16,6 +16,7 @@ package google.registry.model.transfer;
 
 import google.registry.model.Buildable.GenericBuilder;
 import google.registry.model.ImmutableObject;
+import javax.persistence.Column;
 import javax.persistence.EnumType;
 import javax.persistence.Enumerated;
 import javax.persistence.MappedSuperclass;
@@ -38,6 +39,7 @@ public abstract class BaseTransferObject extends ImmutableObject {
 
   /** The gaining registrar of the current or last transfer. Can be null if never transferred. */
   @XmlElement(name = "reID")
+  @Column(name = "transfer_gaining_registrar_id")
   String gainingClientId;
 
   /** The time that the last transfer was requested. Can be null if never transferred. */
@@ -46,6 +48,7 @@ public abstract class BaseTransferObject extends ImmutableObject {
 
   /** The losing registrar of the current or last transfer. Can be null if never transferred. */
   @XmlElement(name = "acID")
+  @Column(name = "transfer_losing_registrar_id")
   String losingClientId;
 
   /**
@@ -54,6 +57,7 @@ public abstract class BaseTransferObject extends ImmutableObject {
    * this holds the time that the last pending transfer ended. Can be null if never transferred.
    */
   @XmlElement(name = "acDate")
+  @Column(name = "transfer_pending_expiration_time")
   DateTime pendingTransferExpirationTime;
 
   public TransferStatus getTransferStatus() {

core/src/main/java/google/registry/model/transfer/TransferData.java

@@ -17,8 +17,8 @@ package google.registry.model.transfer;
 import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
 
 import com.google.common.collect.ImmutableSet;
-import com.googlecode.objectify.Key;
 import com.googlecode.objectify.annotation.Embed;
+import com.googlecode.objectify.annotation.Ignore;
 import com.googlecode.objectify.annotation.IgnoreSave;
 import com.googlecode.objectify.annotation.Unindex;
 import com.googlecode.objectify.condition.IfNull;
@@ -29,10 +29,14 @@ import google.registry.model.domain.Period;
 import google.registry.model.domain.Period.Unit;
 import google.registry.model.eppcommon.Trid;
 import google.registry.model.poll.PollMessage;
+import google.registry.persistence.VKey;
 import java.util.Set;
 import javax.annotation.Nullable;
-import javax.persistence.ElementCollection;
+import javax.persistence.AttributeOverride;
+import javax.persistence.AttributeOverrides;
+import javax.persistence.Column;
 import javax.persistence.Embedded;
+import javax.persistence.Transient;
 import org.joda.time.DateTime;
 
 /**
@@ -47,7 +51,16 @@ public class TransferData extends BaseTransferObject implements Buildable {
   public static final TransferData EMPTY = new TransferData();
 
   /** The transaction id of the most recent transfer request (or null if there never was one). */
-  @Embedded Trid transferRequestTrid;
+  @Embedded
+  @AttributeOverrides({
+    @AttributeOverride(
+        name = "serverTransactionId",
+        column = @Column(name = "transfer_server_txn_id")),
+    @AttributeOverride(
+        name = "clientTransactionId",
+        column = @Column(name = "transfer_client_txn_id"))
+  })
+  Trid transferRequestTrid;
 
   /**
    * The period to extend the registration upon completion of the transfer.
@@ -55,23 +68,29 @@ public class TransferData extends BaseTransferObject implements Buildable {
    * <p>By default, domain transfers are for one year. This can be changed to zero by using the
    * superuser EPP extension.
    */
-  @Embedded Period transferPeriod = Period.create(1, Unit.YEARS);
+  @Embedded
+  @AttributeOverrides({
+    @AttributeOverride(name = "unit", column = @Column(name = "transfer_renew_period_unit")),
+    @AttributeOverride(name = "value", column = @Column(name = "transfer_renew_period_value"))
+  })
+  Period transferPeriod = Period.create(1, Unit.YEARS);
 
   /**
    * The registration expiration time resulting from the approval - speculative or actual - of the
    * most recent transfer request, applicable for domains only.
    *
    * <p>For pending transfers, this is the expiration time that will take effect under a projected
-   * server approval. For approved transfers, this is the actual expiration time of the domain as
-   * of the moment of transfer completion. For rejected or cancelled transfers, this field will be
+   * server approval. For approved transfers, this is the actual expiration time of the domain as of
+   * the moment of transfer completion. For rejected or cancelled transfers, this field will be
    * reset to null.
    *
    * <p>Note that even when this field is set, it does not necessarily mean that the post-transfer
-   * domain has a new expiration time.  Superuser transfers may not include a bundled 1 year renewal
+   * domain has a new expiration time. Superuser transfers may not include a bundled 1 year renewal
    * at all, or even when a renewal is bundled, for a transfer during the autorenew grace period the
    * bundled renewal simply subsumes the recent autorenewal, resulting in the same expiration time.
    */
   // TODO(b/36405140): backfill this field for existing domains to which it should apply.
+  @Column(name = "transfer_registration_expiration_time")
   DateTime transferredRegistrationExpirationTime;
 
   /**
@@ -83,18 +102,35 @@ public class TransferData extends BaseTransferObject implements Buildable {
    * pending transfer is explicitly approved, rejected or cancelled, the referenced entities should
    * be deleted.
    */
+  @Transient
   @IgnoreSave(IfNull.class)
-  @ElementCollection
-  Set<Key<? extends TransferServerApproveEntity>> serverApproveEntities;
+  Set<VKey<? extends TransferServerApproveEntity>> serverApproveEntities;
+
+  // The following 3 fields are the replacement for serverApproveEntities in Cloud SQL.
+  // TODO(shicong): Add getter/setter for these 3 fields and use them in the application code.
+  @Ignore
+  @Column(name = "transfer_gaining_poll_message_id")
+  Long gainingTransferPollMessageId;
+
+  @Ignore
+  @Column(name = "transfer_losing_poll_message_id")
+  Long losingTransferPollMessageId;
+
+  @Ignore
+  @Column(name = "transfer_billing_cancellation_id")
+  Long billingCancellationId;
 
   /**
    * The regular one-time billing event that will be charged for a server-approved transfer.
    *
    * <p>This field should be null if there is not currently a pending transfer or if the object
    * being transferred is not a domain.
+   *
+   * <p>TODO(b/158230654) Remove unused columns for TransferData in Contact table.
    */
   @IgnoreSave(IfNull.class)
-  Key<BillingEvent.OneTime> serverApproveBillingEvent;
+  @Column(name = "transfer_billing_event_id")
+  VKey<BillingEvent.OneTime> serverApproveBillingEvent;
 
   /**
    * The autorenew billing event that should be associated with this resource after the transfer.
@@ -103,7 +139,8 @@ public class TransferData extends BaseTransferObject implements Buildable {
    * being transferred is not a domain.
    */
   @IgnoreSave(IfNull.class)
-  Key<BillingEvent.Recurring> serverApproveAutorenewEvent;
+  @Column(name = "transfer_billing_recurrence_id")
+  VKey<BillingEvent.Recurring> serverApproveAutorenewEvent;
 
   /**
    * The autorenew poll message that should be associated with this resource after the transfer.
@@ -112,7 +149,8 @@ public class TransferData extends BaseTransferObject implements Buildable {
    * being transferred is not a domain.
    */
   @IgnoreSave(IfNull.class)
-  Key<PollMessage.Autorenew> serverApproveAutorenewPollMessage;
+  @Column(name = "transfer_autorenew_poll_message_id")
+  VKey<PollMessage.Autorenew> serverApproveAutorenewPollMessage;
 
   @Nullable
   public Trid getTransferRequestTrid() {
@@ -128,22 +166,22 @@ public class TransferData extends BaseTransferObject implements Buildable {
     return transferredRegistrationExpirationTime;
   }
 
-  public ImmutableSet<Key<? extends TransferServerApproveEntity>> getServerApproveEntities() {
+  public ImmutableSet<VKey<? extends TransferServerApproveEntity>> getServerApproveEntities() {
     return nullToEmptyImmutableCopy(serverApproveEntities);
   }
 
   @Nullable
-  public Key<BillingEvent.OneTime> getServerApproveBillingEvent() {
+  public VKey<BillingEvent.OneTime> getServerApproveBillingEvent() {
     return serverApproveBillingEvent;
   }
 
   @Nullable
-  public Key<BillingEvent.Recurring> getServerApproveAutorenewEvent() {
+  public VKey<BillingEvent.Recurring> getServerApproveAutorenewEvent() {
     return serverApproveAutorenewEvent;
   }
 
   @Nullable
-  public Key<PollMessage.Autorenew> getServerApproveAutorenewPollMessage() {
+  public VKey<PollMessage.Autorenew> getServerApproveAutorenewPollMessage() {
     return serverApproveAutorenewPollMessage;
   }
 
@@ -202,25 +240,25 @@ public class TransferData extends BaseTransferObject implements Buildable {
     }
 
     public Builder setServerApproveEntities(
-        ImmutableSet<Key<? extends TransferServerApproveEntity>> serverApproveEntities) {
+        ImmutableSet<VKey<? extends TransferServerApproveEntity>> serverApproveEntities) {
       getInstance().serverApproveEntities = serverApproveEntities;
       return this;
     }
 
     public Builder setServerApproveBillingEvent(
-        Key<BillingEvent.OneTime> serverApproveBillingEvent) {
+        VKey<BillingEvent.OneTime> serverApproveBillingEvent) {
       getInstance().serverApproveBillingEvent = serverApproveBillingEvent;
       return this;
     }
 
     public Builder setServerApproveAutorenewEvent(
-        Key<BillingEvent.Recurring> serverApproveAutorenewEvent) {
+        VKey<BillingEvent.Recurring> serverApproveAutorenewEvent) {
       getInstance().serverApproveAutorenewEvent = serverApproveAutorenewEvent;
       return this;
     }
 
     public Builder setServerApproveAutorenewPollMessage(
-        Key<PollMessage.Autorenew> serverApproveAutorenewPollMessage) {
+        VKey<PollMessage.Autorenew> serverApproveAutorenewPollMessage) {
       getInstance().serverApproveAutorenewPollMessage = serverApproveAutorenewPollMessage;
       return this;
     }
@@ -230,5 +268,7 @@ public class TransferData extends BaseTransferObject implements Buildable {
    * Marker interface for objects that are written in anticipation of a server approval, and
    * therefore need to be deleted under any other outcome.
    */
-  public interface TransferServerApproveEntity {}
+  public interface TransferServerApproveEntity {
+    VKey<? extends TransferServerApproveEntity> createVKey();
+  }
 }

core/src/main/java/google/registry/persistence/VKey.java

@@ -17,6 +17,7 @@ package google.registry.persistence;
 import static com.google.common.base.Preconditions.checkState;
 import static google.registry.util.PreconditionsUtils.checkArgumentNotNull;
 
+import com.googlecode.objectify.Key;
 import google.registry.model.ImmutableObject;
 import java.util.Optional;
 
@@ -57,6 +58,23 @@ public class VKey<T> extends ImmutableObject {
     return new VKey(kind, ofyKey, null);
   }
 
+  /**
+   * Creates a {@link VKey} which only contains the ofy primary key by specifying the id of the
+   * {@link Key}.
+   */
+  public static <T> VKey<T> createOfy(Class<? extends T> kind, long id) {
+    return createOfy(kind, Key.create(kind, id));
+  }
+
+  /**
+   * Creates a {@link VKey} which only contains the ofy primary key by specifying the name of the
+   * {@link Key}.
+   */
+  public static <T> VKey<T> createOfy(Class<? extends T> kind, String name) {
+    checkArgumentNotNull(kind, "name must not be null");
+    return createOfy(kind, Key.create(kind, name));
+  }
+
   /** Creates a {@link VKey} which only contains both sql and ofy primary key. */
   public static <T> VKey<T> create(
       Class<? extends T> kind, Object sqlKey, com.googlecode.objectify.Key ofyKey) {

core/src/main/java/google/registry/persistence/converter/TransferServerApproveEntitySetConverter.java

@@ -0,0 +1,37 @@
+// Copyright 2020 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.persistence.converter;
+
+import google.registry.model.transfer.TransferData.TransferServerApproveEntity;
+import google.registry.persistence.VKey;
+import java.util.Set;
+import javax.persistence.AttributeConverter;
+import javax.persistence.Converter;
+
+/** {@link AttributeConverter} for {@link Set}. */
+@Converter(autoApply = true)
+public class TransferServerApproveEntitySetConverter
+    extends StringSetConverterBase<VKey<? extends TransferServerApproveEntity>> {
+
+  @Override
+  String toString(VKey<? extends TransferServerApproveEntity> element) {
+    return String.valueOf(element.getSqlKey());
+  }
+
+  @Override
+  VKey<? extends TransferServerApproveEntity> fromString(String value) {
+    return VKey.createSql(TransferServerApproveEntity.class, Long.parseLong(value));
+  }
+}

core/src/main/resources/META-INF/persistence.xml

@@ -56,15 +56,18 @@
     <class>google.registry.persistence.converter.StringListConverter</class>
     <class>google.registry.persistence.converter.StringSetConverter</class>
     <class>google.registry.persistence.converter.TldStateTransitionConverter</class>
+    <class>google.registry.persistence.converter.TransferServerApproveEntitySetConverter</class>
     <class>google.registry.persistence.converter.UpdateAutoTimestampConverter</class>
     <class>google.registry.persistence.converter.ZonedDateTimeConverter</class>
 
     <!-- Generated converters for VKey -->
     <class>google.registry.model.billing.VKeyConverter_BillingEvent</class>
     <class>google.registry.model.domain.VKeyConverter_DomainBase</class>
+    <class>google.registry.model.contact.VKeyConverter_ContactResource</class>
     <class>google.registry.model.domain.token.VKeyConverter_AllocationToken</class>
     <class>google.registry.model.host.VKeyConverter_HostResource</class>
-    <class>google.registry.model.contact.VKeyConverter_ContactResource</class>
+    <class>google.registry.model.poll.VKeyConverter_Autorenew</class>
+    <class>google.registry.model.poll.VKeyConverter_OneTime</class>
 
     <!-- TODO(weiminyu): check out application-layer validation. -->
     <validation-mode>NONE</validation-mode>