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cachedresult.h

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00001 /*-------------------------------------------------------------------------
00002  *
00003  *   FILE
00004  *      pqxx/cachedresult.h
00005  *
00006  *   DESCRIPTION
00007  *      definitions for the pqxx::cachedresult class and support classes.
00008  *   pqxx::cachedresult is a lazy-fetching, transparently-cached result set
00009  *
00010  * Copyright (c) 2001-2003, Jeroen T. Vermeulen <jtv@xs4all.nl>
00011  *
00012  * See COPYING for copyright license.  If you did not receive a file called
00013  * COPYING with this source code, please notify the distributor of this mistake,
00014  * or contact the author.
00015  *
00016  *-------------------------------------------------------------------------
00017  */
00018 #ifndef PQXX_CACHEDRESULT_H
00019 #define PQXX_CACHEDRESULT_H
00020 
00021 #include <map>
00022 
00023 #include "pqxx/cursor.h"
00024 #include "pqxx/result.h"
00025 
00026 namespace pqxx
00027 {
00028 
00050 class PQXX_LIBEXPORT cachedresult
00051 {
00052 public:
00053   typedef result::size_type size_type;
00054   typedef size_type blocknum;
00055 
00057   typedef result::tuple tuple;
00058 
00060   typedef tuple Tuple;
00061 
00073   template<typename TRANSACTION> explicit
00074     cachedresult(TRANSACTION &T,
00075                  const char Query[],
00076                  const PGSTD::string &BaseName="query",
00077                  size_type Granularity=100) :                           //[t40]
00078       m_Granularity(Granularity),
00079       m_Cache(),
00080       m_Cursor(T, Query, BaseName, Granularity),
00081       m_EmptyResult(),
00082       m_HaveEmpty(false)
00083   {
00084     // Trigger build error if T has insufficient isolation level
00085     error_permitted_isolation_level(PQXX_TYPENAME TRANSACTION::isolation_tag());
00086     init();
00087   }
00088 
00089 
00091 
00099   const tuple operator[](size_type i) const                             //[t41]
00100         { return GetBlock(BlockFor(i))[Offset(i)]; }
00101 
00103 
00114    const tuple at(size_type i) const                                    //[t40]
00115         { return GetBlock(BlockFor(i)).at(Offset(i)); }
00116 
00118   size_type size() const;                                               //[t40]
00119   
00121   bool empty() const;                                                   //[t47]
00122 
00123 private:
00124   typedef Cursor::pos pos;
00125 
00126 #ifndef PQXX_WORKAROUND_VC7
00127 
00128 
00133   template<typename ISOLATIONTAG>
00134     static inline void error_permitted_isolation_level(ISOLATIONTAG) throw();
00135 #else
00136   // Incorrect, but needed to compile with Visual C++ 7
00137   template<> static inline void
00138     error_permitted_isolation_level(isolation_traits<serializable>) throw ();
00139 #endif
00140 
00141   void init();
00142 
00143   blocknum BlockFor(size_type Row) const throw () 
00144         { return Row / m_Granularity; }
00145   size_type Offset(size_type Row) const throw ()
00146         { return Row % m_Granularity; }
00147   Cursor::size_type FirstRowOf(blocknum Block) const throw ()
00148         { return Block*m_Granularity; }
00149 
00150   void MoveTo(blocknum) const;
00151 
00153   const result &Fetch() const;
00154 
00155   const result &GetBlock(blocknum b) const
00156   {
00157     CacheMap::const_iterator i = m_Cache.find(b);
00158     if (i != m_Cache.end()) return i->second;
00159 
00160     MoveTo(b);
00161     return Fetch();
00162   }
00163 
00165   size_type m_Granularity;
00166 
00167   typedef PGSTD::map<blocknum, result> CacheMap;
00168   mutable CacheMap m_Cache;
00169 
00170   mutable Cursor m_Cursor;
00171   mutable result m_EmptyResult;
00172   mutable bool   m_HaveEmpty;
00173 
00174   // Not allowed:
00175   cachedresult();
00176   cachedresult(const cachedresult &);
00177   cachedresult &operator=(const cachedresult &);
00178 };
00179 
00181 typedef cachedresult CachedResult;
00182 
00183 template<> inline void
00184 cachedresult::error_permitted_isolation_level(isolation_traits<serializable>)
00185   throw () {}
00186 
00187 } // namespace pqxx
00188 
00189 #endif
00190 

Generated on Thu Dec 25 07:22:37 2003 for libpqxx by doxygen 1.3.4