Create a class to represent a DOM Storage Database.

webkit/dom_storage/dom_storage_database.h

+// 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.
+
+#ifndef WEBKIT_DOM_STORAGE_DOM_STORAGE_DATABASE_H_
+#define WEBKIT_DOM_STORAGE_DOM_STORAGE_DATABASE_H_
+
+#include <map>
+#include <set>
+
+#include "base/file_path.h"
+#include "base/gtest_prod_util.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/string16.h"
+#include "sql/connection.h"
+
+namespace dom_storage {
+
+// Represents a SQLite based backing for DOM storage data. This
+// class is designed to be used on a single thread.
+class DomStorageDatabase {
+ public:
+  explicit DomStorageDatabase(const FilePath& file_path);
+  ~DomStorageDatabase();
+
+  typedef std::map<string16, string16> ValuesMap;
+  typedef std::set<string16> ValuesSet;
+
+  // Reads all the key, value pairs stored in the database and returns
+  // them.
+  void ReadAllValues(ValuesMap* result);
+
+  // Write all |values| into the database, overwriting previously set
+  // keys and values.
+  bool WriteValues(const ValuesMap& values);

[michaeln, 2012/01/31 22:45:32]

With the current public interface, there is no way to update a value and delete
another in the same transaction. My model for how changes gets committed is that
changes accrue in memory until  some amount of time has past, and then those
changes get committed atomically so what results in the db exactly matches an
instance of what was in memory at some point in time. With that in mind, wdyt
about a public api that looks like this...

typedef std::map<string16, NullableString16> ValuesMap;

// Reads all values from the database and populates the
// |all_values| map with non-null NullableString16 results.
// The |all_values| collection is expected to be initially empty. If
// the backing database file does not exist upon entry, none will not
// be created on disk.
bool ReadAll(ValueMap* all_values);

// Inserts, updates, or deletes the values in the |changed_values|
// collection, null NullableString16 values are deleted from the database,
// non-null NullableString16 values are inserted or updated. 
// If |clear_all_first| is true, any existing values in the
// database file are deleted prior to applying the inserts and updates.
// If the backing database file does not exist, one will be created only
// if |changed_values| is non-empty.
bool CommitChanges(bool clear_all_first, const ValueMap& changed_values);

DomStorageArea would keep two collections in memory, all_values_ and
changed_values_, the latter representing inserts/updates/deletes.

[benm (inactive), 2012/02/01 15:42:09]

Like it!

+
+  // Removes the |keys| and their mappings from the database.
+  bool RemoveValues(const ValuesSet& keys);
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest, SimpleOpenAndClose);
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest,
+                           TestUpgradesV1TableToV2);
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest, TestIsOpen);
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest, SimpleRead);
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest, SimpleWrite);
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest, UpgradeFromV1ToV2NoData);
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest,
+                           UpgradeFromV1ToV2WithData);
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest,
+                           TestOpenCloseDataPreserved);
+  FRIEND_TEST_ALL_PREFIXES(DomStorageDatabaseTest, TestSimpleRemoveOneValue);
+
+  // Open the database at file_path_, creating it if it does not exist.
+  // Ensures we are at the correct database version and creates or updates
+  // tables as necessary. Returns false on failure.
+  bool LazyOpen();

[michaeln, 2012/01/31 22:45:32]

If we can avoid creating files on disk, all the better. Wdyt about adding a
'create_if_needed' flag to this method. For ReadAll() it would pass false, and
for CommitChanges it would pass true if changed_values is non-emtpy.

[benm (inactive), 2012/02/01 15:42:09]

OK, I guess we need to check if the file exists too and go and ahead and open
the database regardless of the create_if_needed flag. 

+
+  // Creates the ItemTable at the current version of the database.
+  bool CreateTable();
+  bool CreateTableV2();
+
+  // Version 1 -> 2 migrated the value column in the ItemTable from a TEXT
+  // to a BLOB. Exisitng data is preserved.
+  bool UpgradeVersion1To2IfNeeded();
+
+  void Close();
+  bool IsOpen() const { return db_.get() ? db_->is_open() : false; }
+
+  // Path to the database on disk.
+  FilePath file_path_;
+  scoped_ptr<sql::Connection> db_;
+};
+
+}  // namespace dom_storage
+
+#endif  // WEBKIT_DOM_STORAGE_DOM_STORAGE_DATABASE_H_