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// 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 SQL_META_TABLE_H_
#define SQL_META_TABLE_H_
#include <stdint.h>
#include <string>
#include "base/component_export.h"
#include "base/macros.h"
namespace sql {
class Database;
class Statement;
// Creates and manages a table to store generic metadata. The features provided
// are:
// * An interface for storing multi-typed key-value data.
// * Helper methods to assist in database schema version control.
// * Historical data on past attempts to mmap the database to make it possible
// to avoid unconditionally retrying to load broken databases.
class COMPONENT_EXPORT(SQL) MetaTable {
public:
MetaTable();
~MetaTable();
// Values for Get/SetMmapStatus(). |kMmapFailure| indicates that there was at
// some point a read error and the database should not be memory-mapped, while
// |kMmapSuccess| indicates that the entire file was read at some point and
// can be memory-mapped without constraint.
static constexpr int64_t kMmapFailure = -2;
static constexpr int64_t kMmapSuccess = -1;
// Returns true if the 'meta' table exists.
static bool DoesTableExist(Database* db);
// If the current version of the database is less than or equal to
// |deprecated_version|, raze the database. Must be called outside of a
// transaction.
// TODO(shess): At this time the database is razed IFF meta exists and
// contains a version row with value <= deprecated_version. It may make sense
// to also raze if meta exists but has no version row, or if meta doesn't
// exist. In those cases if the database is not already empty, it probably
// resulted from a broken initialization.
// TODO(shess): Folding this into Init() would allow enforcing
// |deprecated_version|<|version|. But Init() is often called in a
// transaction.
static void RazeIfDeprecated(Database* db, int deprecated_version);
// Used to tuck some data into the meta table about mmap status. The value
// represents how much data in bytes has successfully been read from the
// database, or |kMmapFailure| or |kMmapSuccess|.
static bool GetMmapStatus(Database* db, int64_t* status);
static bool SetMmapStatus(Database* db, int64_t status);
// Initializes the MetaTableHelper, providing the |Database| pointer and
// creating the meta table if necessary. Must be called before any other
// non-static methods. For new tables, it will initialize the version number
// to |version| and the compatible version number to |compatible_version|.
// Versions must be greater than 0 to distinguish missing versions (see
// GetVersionNumber()). If there was no meta table (proxy for a fresh
// database), mmap status is set to |kMmapSuccess|.
bool Init(Database* db, int version, int compatible_version);
// Resets this MetaTable object, making another call to Init() possible.
void Reset();
// The version number of the database. This should be the version number of
// the creator of the file. The version number will be 0 if there is no
// previously set version number.
//
// See also Get/SetCompatibleVersionNumber().
void SetVersionNumber(int version);
int GetVersionNumber();
// The compatible version number is the lowest version of the code that this
// database can be read by. If there are minor changes or additions, old
// versions of the code can still work with the database without failing.
//
// For example, if an optional column is added to a table in version 3, the
// new code will set the version to 3, and the compatible version to 2, since
// the code expecting version 2 databases can still read and write the table.
//
// Rule of thumb: check the version number when you're upgrading, but check
// the compatible version number to see if you can read the file at all. If
// it's larger than you code is expecting, fail.
//
// The compatible version number will be 0 if there is no previously set
// compatible version number.
void SetCompatibleVersionNumber(int version);
int GetCompatibleVersionNumber();
// Set the given arbitrary key with the given data. Returns true on success.
bool SetValue(const char* key, const std::string& value);
bool SetValue(const char* key, int value);
bool SetValue(const char* key, int64_t value);
// Retrieves the value associated with the given key. This will use sqlite's
// type conversion rules. It will return true on success.
bool GetValue(const char* key, std::string* value);
bool GetValue(const char* key, int* value);
bool GetValue(const char* key, int64_t* value);
// Deletes the key from the table.
bool DeleteKey(const char* key);
private:
// Conveniences to prepare the two types of statements used by
// MetaTableHelper.
void PrepareSetStatement(Statement* statement, const char* key);
bool PrepareGetStatement(Statement* statement, const char* key);
Database* db_ = nullptr;
DISALLOW_COPY_AND_ASSIGN(MetaTable);
};
} // namespace sql
#endif // SQL_META_TABLE_H_