Fix caching of /detail for modified reviewer lists

Rely only on ETag for change entity caching. The Last-Modified
value was derived from the lastUpdatedOn property, which is not
always modified when children are updated.

When adding or removing reviewers from a change perform a no-op
modification of the Change entity. This bumps its rowVersion as
a side-effect of the database mutation, causing the ETag to be
different on the next read.

Change-Id: If480f92b419041e7d62839ab12211058e78f828f

gerrit-server/src/main/java/com/google/gerrit/server/ChangeUtil.java

@@ -117,6 +117,15 @@ public class ChangeUtil {
     }
   }
 
+  public static void bumpRowVersionNotLastUpdatedOn(Change.Id id, ReviewDb db)
+      throws OrmException {
+    // Empty update of Change to bump rowVersion, changing its ETag.
+    Change c = db.changes().get(id);
+    if (c != null) {
+      db.changes().update(Collections.singleton(c));
+    }
+  }
+
   public static void updated(final Change c) {
     c.resetLastUpdatedOn();
     computeSortKey(c);

gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeResource.java

@@ -16,16 +16,12 @@ package com.google.gerrit.server.change;
 
 import com.google.gerrit.extensions.restapi.RestResource;
 import com.google.gerrit.extensions.restapi.RestResource.HasETag;
-import com.google.gerrit.extensions.restapi.RestResource.HasLastModified;
 import com.google.gerrit.extensions.restapi.RestView;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.server.project.ChangeControl;
 import com.google.inject.TypeLiteral;
 
-import java.sql.Timestamp;
-
-public class ChangeResource implements RestResource,
-    HasLastModified, HasETag {
+public class ChangeResource implements RestResource, HasETag {
   public static final TypeLiteral<RestView<ChangeResource>> CHANGE_KIND =
       new TypeLiteral<RestView<ChangeResource>>() {};
 
@@ -47,11 +43,6 @@ public class ChangeResource implements RestResource,
     return getControl().getChange();
   }
 
-  @Override
-  public Timestamp getLastModified() {
-    return getChange().getLastUpdatedOn();
-  }
-
   @Override
   public String getETag() {
     return String.format("%x-%x",

gerrit-server/src/main/java/com/google/gerrit/server/change/DeleteReviewer.java

@@ -25,6 +25,7 @@ import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.PatchSetApproval;
 import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.ChangeUtil;
 import com.google.gerrit.server.change.DeleteReviewer.Input;
 import com.google.gerrit.server.project.ChangeControl;
 import com.google.gwtorm.server.OrmException;
@@ -63,6 +64,7 @@ public class DeleteReviewer implements RestModifyView<ReviewerResource, Input> {
       if (del.isEmpty()) {
         throw new ResourceNotFoundException();
       }
+      ChangeUtil.bumpRowVersionNotLastUpdatedOn(rsrc.getChange().getId(), db);
       db.patchSetApprovals().delete(del);
       db.commit();
     } finally {

gerrit-server/src/main/java/com/google/gerrit/server/change/PostReviewers.java

@@ -37,6 +37,7 @@ import com.google.gerrit.reviewdb.client.PatchSet;
 import com.google.gerrit.reviewdb.client.PatchSetApproval;
 import com.google.gerrit.reviewdb.client.PatchSetApproval.LabelId;
 import com.google.gerrit.reviewdb.server.ReviewDb;
+import com.google.gerrit.server.ChangeUtil;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.account.AccountCache;
 import com.google.gerrit.server.account.AccountInfo;
@@ -81,7 +82,7 @@ public class PostReviewers implements RestModifyView<ChangeResource, Input> {
   private final Provider<GroupsCollection> groupsCollection;
   private final GroupMembers.Factory groupMembersFactory;
   private final AccountInfo.Loader.Factory accountLoaderFactory;
-  private final Provider<ReviewDb> db;
+  private final Provider<ReviewDb> dbProvider;
   private final IdentifiedUser currentUser;
   private final IdentifiedUser.GenericFactory identifiedUserFactory;
   private final Config cfg;
@@ -109,7 +110,7 @@ public class PostReviewers implements RestModifyView<ChangeResource, Input> {
     this.groupsCollection = groupsCollection;
     this.groupMembersFactory = groupMembersFactory;
     this.accountLoaderFactory = accountLoaderFactory;
-    this.db = db;
+    this.dbProvider = db;
     this.currentUser = currentUser;
     this.identifiedUserFactory = identifiedUserFactory;
     this.cfg = cfg;
@@ -215,9 +216,10 @@ public class PostReviewers implements RestModifyView<ChangeResource, Input> {
       return;
     }
 
+    ReviewDb db = dbProvider.get();
     PatchSet.Id psid = rsrc.getChange().currentPatchSetId();
     Set<Account.Id> existing = Sets.newHashSet();
-    for (PatchSetApproval psa : db.get().patchSetApprovals().byPatchSet(psid)) {
+    for (PatchSetApproval psa : db.patchSetApprovals().byPatchSet(psid)) {
       existing.add(psa.getAccountId());
     }
 
@@ -235,7 +237,19 @@ public class PostReviewers implements RestModifyView<ChangeResource, Input> {
           new ReviewerInfo(id), control, ImmutableList.of(psa)));
       toInsert.add(psa);
     }
-    db.get().patchSetApprovals().insert(toInsert);
+    if (toInsert.isEmpty()) {
+      return;
+    }
+
+    db.changes().beginTransaction(rsrc.getChange().getId());
+    try {
+      ChangeUtil.bumpRowVersionNotLastUpdatedOn(rsrc.getChange().getId(), db);
+      db.patchSetApprovals().insert(toInsert);
+      db.commit();
+    } finally {
+      db.rollback();
+    }
+
     accountLoaderFactory.create(true).fill(result.reviewers);
     postAdd(rsrc.getChange(), result);
   }
@@ -248,10 +262,10 @@ public class PostReviewers implements RestModifyView<ChangeResource, Input> {
 
     // Execute hook for added reviewers
     //
-    PatchSet patchSet = db.get().patchSets().get(change.currentPatchSetId());
+    PatchSet patchSet = dbProvider.get().patchSets().get(change.currentPatchSetId());
     for (AccountInfo info : result.reviewers) {
       Account account = accountCache.get(info._id).getAccount();
-      hooks.doReviewerAddedHook(change, account, patchSet, db.get());
+      hooks.doReviewerAddedHook(change, account, patchSet, dbProvider.get());
     }
 
     // Email the reviewers