com.google.gerrit.server.schema.NotesMigrationSchemaFactory Maven / Gradle / Ivy
// Copyright (C) 2016 The Android Open Source Project
//
// 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 com.google.gerrit.server.schema;
import com.google.gerrit.reviewdb.server.DisallowReadFromChangesReviewDbWrapper;
import com.google.gerrit.reviewdb.server.ReviewDb;
import com.google.gerrit.server.notedb.NotesMigration;
import com.google.gwtorm.server.OrmException;
import com.google.gwtorm.server.SchemaFactory;
import com.google.inject.Inject;
import com.google.inject.Singleton;
@Singleton
public class NotesMigrationSchemaFactory implements SchemaFactory {
private final SchemaFactory delegate;
private final NotesMigration migration;
@Inject
NotesMigrationSchemaFactory(
@ReviewDbFactory SchemaFactory delegate, NotesMigration migration) {
this.delegate = delegate;
this.migration = migration;
}
@Override
public ReviewDb open() throws OrmException {
ReviewDb db = delegate.open();
if (!migration.readChanges()) {
return db;
}
// There are two levels at which this class disables access to Changes and related tables,
// corresponding to two phases of the NoteDb migration:
//
// 1. When changes are read from NoteDb but some changes might still have their primary storage
// in ReviewDb, it is generally programmer error to read changes from ReviewDb. However,
// since ReviewDb is still the primary storage for most or all changes, we still need to
// support writing to ReviewDb. This behavior is accomplished by wrapping in a
// DisallowReadFromChangesReviewDbWrapper.
//
// Some codepaths might need to be able to read from ReviewDb if they really need to, because
// they need to operate on the underlying source of truth, for example when reading a change
// to determine its primary storage. To support this, ReviewDbUtil#unwrapDb can detect and
// unwrap databases of this type.
//
// 2. After all changes have their primary storage in NoteDb, we can completely shut off access
// to the change tables. At this point in the migration, we are by definition not using the
// ReviewDb tables at all; we could even delete the tables at this point, and Gerrit would
// continue to function.
//
// This is accomplished by setting the delegate ReviewDb *underneath* DisallowReadFromChanges
// to be a complete no-op, with NoChangesReviewDbWrapper. With this wrapper, all read
// operations return no results, and write operations silently do nothing. This wrapper is
// not a public class and nobody should ever attempt to unwrap it.
if (migration.disableChangeReviewDb()) {
db = new NoChangesReviewDbWrapper(db);
}
return new DisallowReadFromChangesReviewDbWrapper(db);
}
}