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   // 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_