1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef SQL_META_TABLE_H_ 6 #define SQL_META_TABLE_H_ 7 8 #include <string> 9 10 #include "base/basictypes.h" 11 #include "sql/sql_export.h" 12 13 namespace sql { 14 15 class Connection; 16 class Statement; 17 18 class SQL_EXPORT MetaTable { 19 public: 20 MetaTable(); 21 ~MetaTable(); 22 23 // Returns true if the 'meta' table exists. 24 static bool DoesTableExist(Connection* db); 25 26 // If the current version of the database is less than or equal to 27 // |deprecated_version|, raze the database. Must be called outside 28 // of a transaction. 29 // TODO(shess): At this time the database is razed IFF meta exists 30 // and contains a version row with value <= deprecated_version. It 31 // may make sense to also raze if meta exists but has no version 32 // row, or if meta doesn't exist. In those cases if the database is 33 // not already empty, it probably resulted from a broken 34 // initialization. 35 // TODO(shess): Folding this into Init() would allow enforcing 36 // |deprecated_version|<|version|. But Init() is often called in a 37 // transaction. 38 static void RazeIfDeprecated(Connection* db, int deprecated_version); 39 40 // Initializes the MetaTableHelper, creating the meta table if necessary. For 41 // new tables, it will initialize the version number to |version| and the 42 // compatible version number to |compatible_version|. Versions must be 43 // greater than 0 to distinguish missing versions (see GetVersionNumber()). 44 bool Init(Connection* db, int version, int compatible_version); 45 46 // Resets this MetaTable object, making another call to Init() possible. 47 void Reset(); 48 49 // The version number of the database. This should be the version number of 50 // the creator of the file. The version number will be 0 if there is no 51 // previously set version number. 52 // 53 // See also Get/SetCompatibleVersionNumber(). 54 void SetVersionNumber(int version); 55 int GetVersionNumber(); 56 57 // The compatible version number is the lowest version of the code that this 58 // database can be read by. If there are minor changes or additions, old 59 // versions of the code can still work with the database without failing. 60 // 61 // For example, if an optional column is added to a table in version 3, the 62 // new code will set the version to 3, and the compatible version to 2, since 63 // the code expecting version 2 databases can still read and write the table. 64 // 65 // Rule of thumb: check the version number when you're upgrading, but check 66 // the compatible version number to see if you can read the file at all. If 67 // it's larger than you code is expecting, fail. 68 // 69 // The compatible version number will be 0 if there is no previously set 70 // compatible version number. 71 void SetCompatibleVersionNumber(int version); 72 int GetCompatibleVersionNumber(); 73 74 // Set the given arbitrary key with the given data. Returns true on success. 75 bool SetValue(const char* key, const std::string& value); 76 bool SetValue(const char* key, int value); 77 bool SetValue(const char* key, int64 value); 78 79 // Retrieves the value associated with the given key. This will use sqlite's 80 // type conversion rules. It will return true on success. 81 bool GetValue(const char* key, std::string* value); 82 bool GetValue(const char* key, int* value); 83 bool GetValue(const char* key, int64* value); 84 85 // Deletes the key from the table. 86 bool DeleteKey(const char* key); 87 88 private: 89 // Conveniences to prepare the two types of statements used by 90 // MetaTableHelper. 91 void PrepareSetStatement(Statement* statement, const char* key); 92 bool PrepareGetStatement(Statement* statement, const char* key); 93 94 Connection* db_; 95 96 DISALLOW_COPY_AND_ASSIGN(MetaTable); 97 }; 98 99 } // namespace sql 100 101 #endif // SQL_META_TABLE_H_ 102
