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 #pragma once
   8
   9 #include <string>
  10
  11 #include "base/basictypes.h"
  12 #include "sql/sql_export.h"
  13
  14 namespace sql {
  15
  16 class Connection;
  17 class Statement;
  18
  19 class SQL_EXPORT MetaTable {
  20  public:
  21   MetaTable();
  22   ~MetaTable();
  23
  24   // Returns true if the 'meta' table exists.
  25   static bool DoesTableExist(Connection* db);
  26
  27   // Initializes the MetaTableHelper, creating the meta table if necessary. For
  28   // new tables, it will initialize the version number to |version| and the
  29   // compatible version number to |compatible_version|.  Versions must be
  30   // greater than 0 to distinguish missing versions (see GetVersionNumber()).
  31   bool Init(Connection* db, int version, int compatible_version);
  32
  33   // Resets this MetaTable object, making another call to Init() possible.
  34   void Reset();
  35
  36   // The version number of the database. This should be the version number of
  37   // the creator of the file. The version number will be 0 if there is no
  38   // previously set version number.
  39   //
  40   // See also Get/SetCompatibleVersionNumber().
  41   void SetVersionNumber(int version);
  42   int GetVersionNumber();
  43
  44   // The compatible version number is the lowest version of the code that this
  45   // database can be read by. If there are minor changes or additions, old
  46   // versions of the code can still work with the database without failing.
  47   //
  48   // For example, if an optional column is added to a table in version 3, the
  49   // new code will set the version to 3, and the compatible version to 2, since
  50   // the code expecting version 2 databases can still read and write the table.
  51   //
  52   // Rule of thumb: check the version number when you're upgrading, but check
  53   // the compatible version number to see if you can read the file at all. If
  54   // it's larger than you code is expecting, fail.
  55   //
  56   // The compatible version number will be 0 if there is no previously set
  57   // compatible version number.
  58   void SetCompatibleVersionNumber(int version);
  59   int GetCompatibleVersionNumber();
  60
  61   // Set the given arbitrary key with the given data. Returns true on success.
  62   bool SetValue(const char* key, const std::string& value);
  63   bool SetValue(const char* key, int value);
  64   bool SetValue(const char* key, int64 value);
  65
  66   // Retrieves the value associated with the given key. This will use sqlite's
  67   // type conversion rules. It will return true on success.
  68   bool GetValue(const char* key, std::string* value);
  69   bool GetValue(const char* key, int* value);
  70   bool GetValue(const char* key, int64* value);
  71
  72   // Deletes the key from the table.
  73   bool DeleteKey(const char* key);
  74
  75  private:
  76   // Conveniences to prepare the two types of statements used by
  77   // MetaTableHelper.
  78   void PrepareSetStatement(Statement* statement, const char* key);
  79   bool PrepareGetStatement(Statement* statement, const char* key);
  80
  81   Connection* db_;
  82
  83   DISALLOW_COPY_AND_ASSIGN(MetaTable);
  84 };
  85
  86 }  // namespace sql
  87
  88 #endif  // SQL_META_TABLE_H_