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 <stdint.h>
   9 #include <string>
  10
  11 #include "base/macros.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   // If the current version of the database is less than or equal to
  28   // |deprecated_version|, raze the database.  Must be called outside
  29   // of a transaction.
  30   // TODO(shess): At this time the database is razed IFF meta exists
  31   // and contains a version row with value <= deprecated_version.  It
  32   // may make sense to also raze if meta exists but has no version
  33   // row, or if meta doesn't exist.  In those cases if the database is
  34   // not already empty, it probably resulted from a broken
  35   // initialization.
  36   // TODO(shess): Folding this into Init() would allow enforcing
  37   // |deprecated_version|<|version|.  But Init() is often called in a
  38   // transaction.
  39   static void RazeIfDeprecated(Connection* db, int deprecated_version);
  40
  41   // Initializes the MetaTableHelper, creating the meta table if necessary. For
  42   // new tables, it will initialize the version number to |version| and the
  43   // compatible version number to |compatible_version|.  Versions must be
  44   // greater than 0 to distinguish missing versions (see GetVersionNumber()).
  45   bool Init(Connection* db, int version, int compatible_version);
  46
  47   // Resets this MetaTable object, making another call to Init() possible.
  48   void Reset();
  49
  50   // The version number of the database. This should be the version number of
  51   // the creator of the file. The version number will be 0 if there is no
  52   // previously set version number.
  53   //
  54   // See also Get/SetCompatibleVersionNumber().
  55   void SetVersionNumber(int version);
  56   int GetVersionNumber();
  57
  58   // The compatible version number is the lowest version of the code that this
  59   // database can be read by. If there are minor changes or additions, old
  60   // versions of the code can still work with the database without failing.
  61   //
  62   // For example, if an optional column is added to a table in version 3, the
  63   // new code will set the version to 3, and the compatible version to 2, since
  64   // the code expecting version 2 databases can still read and write the table.
  65   //
  66   // Rule of thumb: check the version number when you're upgrading, but check
  67   // the compatible version number to see if you can read the file at all. If
  68   // it's larger than you code is expecting, fail.
  69   //
  70   // The compatible version number will be 0 if there is no previously set
  71   // compatible version number.
  72   void SetCompatibleVersionNumber(int version);
  73   int GetCompatibleVersionNumber();
  74
  75   // Set the given arbitrary key with the given data. Returns true on success.
  76   bool SetValue(const char* key, const std::string& value);
  77   bool SetValue(const char* key, int value);
  78   bool SetValue(const char* key, int64_t value);
  79
  80   // Retrieves the value associated with the given key. This will use sqlite's
  81   // type conversion rules. It will return true on success.
  82   bool GetValue(const char* key, std::string* value);
  83   bool GetValue(const char* key, int* value);
  84   bool GetValue(const char* key, int64_t* value);
  85
  86   // Deletes the key from the table.
  87   bool DeleteKey(const char* key);
  88
  89  private:
  90   // Conveniences to prepare the two types of statements used by
  91   // MetaTableHelper.
  92   void PrepareSetStatement(Statement* statement, const char* key);
  93   bool PrepareGetStatement(Statement* statement, const char* key);
  94
  95   Connection* db_;
  96
  97   DISALLOW_COPY_AND_ASSIGN(MetaTable);
  98 };
  99
 100 }  // namespace sql
 101
 102 #endif  // SQL_META_TABLE_H_