sql/meta_table.h

   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   // Initializes the MetaTableHelper, creating the meta table if necessary. For
  27   // new tables, it will initialize the version number to |version| and the
  28   // compatible version number to |compatible_version|.  Versions must be
  29   // greater than 0 to distinguish missing versions (see GetVersionNumber()).
  30   bool Init(Connection* db, int version, int compatible_version);
  31
  32   // Resets this MetaTable object, making another call to Init() possible.
  33   void Reset();
  34
  35   // The version number of the database. This should be the version number of
  36   // the creator of the file. The version number will be 0 if there is no
  37   // previously set version number.
  38   //
  39   // See also Get/SetCompatibleVersionNumber().
  40   void SetVersionNumber(int version);
  41   int GetVersionNumber();
  42
  43   // The compatible version number is the lowest version of the code that this
  44   // database can be read by. If there are minor changes or additions, old
  45   // versions of the code can still work with the database without failing.
  46   //
  47   // For example, if an optional column is added to a table in version 3, the
  48   // new code will set the version to 3, and the compatible version to 2, since
  49   // the code expecting version 2 databases can still read and write the table.
  50   //
  51   // Rule of thumb: check the version number when you're upgrading, but check
  52   // the compatible version number to see if you can read the file at all. If
  53   // it's larger than you code is expecting, fail.
  54   //
  55   // The compatible version number will be 0 if there is no previously set
  56   // compatible version number.
  57   void SetCompatibleVersionNumber(int version);
  58   int GetCompatibleVersionNumber();
  59
  60   // Set the given arbitrary key with the given data. Returns true on success.
  61   bool SetValue(const char* key, const std::string& value);
  62   bool SetValue(const char* key, int value);
  63   bool SetValue(const char* key, int64 value);
  64
  65   // Retrieves the value associated with the given key. This will use sqlite's
  66   // type conversion rules. It will return true on success.
  67   bool GetValue(const char* key, std::string* value);
  68   bool GetValue(const char* key, int* value);
  69   bool GetValue(const char* key, int64* value);
  70
  71   // Deletes the key from the table.
  72   bool DeleteKey(const char* key);
  73
  74  private:
  75   // Conveniences to prepare the two types of statements used by
  76   // MetaTableHelper.
  77   void PrepareSetStatement(Statement* statement, const char* key);
  78   bool PrepareGetStatement(Statement* statement, const char* key);
  79
  80   Connection* db_;
  81
  82   DISALLOW_COPY_AND_ASSIGN(MetaTable);
  83 };
  84
  85 }  // namespace sql
  86
  87 #endif  // SQL_META_TABLE_H_