Create meta table atomically.

sql/meta_table.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sql/meta_table.h"
 
 #include "base/logging.h"
 #include "base/string_util.h"
 #include "sql/connection.h"
 #include "sql/statement.h"
+#include "sql/transaction.h"
 
 namespace sql {
 
 // Key used in our meta table for version numbers.
 static const char kVersionKey[] = "version";
 static const char kCompatibleVersionKey[] = "last_compatible_version";
 
 MetaTable::MetaTable() : db_(NULL) {
 }
 
 MetaTable::~MetaTable() {
 }
 
 // static
 bool MetaTable::DoesTableExist(sql::Connection* db) {
   DCHECK(db);
   return db->DoesTableExist("meta");
 }
 
 bool MetaTable::Init(Connection* db, int version, int compatible_version) {
   DCHECK(!db_ && db);
   db_ = db;
+
+  // If values stored are null or missing entirely, 0 will be reported.
+  // Require new clients to start with a greater initial version.
+  DCHECK_GT(version, 0);
+  DCHECK_GT(compatible_version, 0);
+
+  // Make sure the table is created an populated atomically.

[benjhayden, 2012/03/06 22:34:35]

s/ an / and /

+  sql::Transaction transaction(db_);
+  if (!transaction.Begin())
+    return false;
+
   if (!DoesTableExist(db)) {
     if (!db_->Execute("CREATE TABLE meta"
         "(key LONGVARCHAR NOT NULL UNIQUE PRIMARY KEY, value LONGVARCHAR)"))
       return false;
 
     // Note: there is no index over the meta table. We currently only have a
     // couple of keys, so it doesn't matter. If we start storing more stuff in
     // there, we should create an index.
     SetVersionNumber(version);
     SetCompatibleVersionNumber(compatible_version);
   }
-  return true;
+  return transaction.Commit();
 }
 
 void MetaTable::Reset() {
   db_ = NULL;
 }
 
 void MetaTable::SetVersionNumber(int version) {
+  DCHECK_GT(version, 0);
   SetValue(kVersionKey, version);
 }
 
 int MetaTable::GetVersionNumber() {
   int version = 0;
   return GetValue(kVersionKey, &version) ? version : 0;
 }
 
 void MetaTable::SetCompatibleVersionNumber(int version) {
+  DCHECK_GT(version, 0);
   SetValue(kCompatibleVersionKey, version);
 }
 
 int MetaTable::GetCompatibleVersionNumber() {
   int version = 0;
   return GetValue(kCompatibleVersionKey, &version) ? version : 0;
 }
 
 bool MetaTable::SetValue(const char* key, const std::string& value) {
   Statement s;
@@ skipping 59 matching lines @@
 
 bool MetaTable::PrepareGetStatement(Statement* statement, const char* key) {
   DCHECK(db_ && statement);
   statement->Assign(db_->GetCachedStatement(SQL_FROM_HERE,
       "SELECT value FROM meta WHERE key=?"));
   statement->BindCString(0, key);
   return statement->Step();
 }
 
 }  // namespace sql