| // 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/macros.h" |
| #include "sql/sql_export.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 SQL_EXPORT 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_; |
| |
| DISALLOW_COPY_AND_ASSIGN(MetaTable); |
| }; |
| |
| } // namespace sql |
| |
| #endif // SQL_META_TABLE_H_ |