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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  *-------------------------------------------------------------------------
00013  */
00014 #ifndef PQXX_CACHEDRESULT_H
00015 #define PQXX_CACHEDRESULT_H
00016 
00017 #include <map>
00018 
00019 #include "pqxx/cursor.h"
00020 #include "pqxx/result.h"
00021 
00022 namespace pqxx
00023 {
00024 
00025 class TransactionItf;
00026 
00027 // TODO: Forward-only mode of operation?  Or write separate stream class?
00028 
00046 class PQXX_LIBEXPORT CachedResult
00047 {
00048 public:
00049   typedef Result::size_type size_type;
00050   typedef size_type blocknum;
00051   typedef Result::Tuple Tuple;
00052 
00057   explicit CachedResult(pqxx::TransactionItf &,
00058                         const char Query[],
00059                         const PGSTD::string &BaseName="query",
00060                         size_type Granularity=100);                     //[t40]
00061 
00062   // TODO: Iterators, begin(), end()
00063   // TODO: Metadata
00064   // TODO: Block replacement (limit cache size); then add capacity()
00065 
00066   const Tuple operator[](size_type i) const                             //[t41]
00067         { return GetBlock(BlockFor(i))[Offset(i)]; }
00068 
00069   const Tuple at(size_type i) const                                     //[t40]
00070         { return GetBlock(BlockFor(i)).at(Offset(i)); }
00071 
00073   size_type size() const;                                               //[t40]
00074   
00076   bool empty() const;                                                   //[]
00077 
00079   void clear();                                                         //[]
00080 
00082   class const_iterator
00083   {
00084     const CachedResult &m_Home;
00085     CachedResult::size_type m_Row;
00086   public:
00087     explicit const_iterator(const CachedResult &Home) : m_Home(Home), m_Row(0){}
00088 
00089   private:
00090     // Not allowed:
00091     const_iterator();
00092   };
00093 
00094 private:
00095 
00096   typedef Cursor::pos pos;
00097 
00098   class CacheEntry
00099   {
00100     int m_RefCount;
00101     Result m_Data;
00102 
00103   public:
00104     CacheEntry() : m_RefCount(0), m_Data() {}
00105     explicit CacheEntry(const Result &R) : m_RefCount(0), m_Data(R) {}
00106 
00107     const Result &Data() const { return m_Data; }
00108     int RefCount() const { return m_RefCount; }
00109   };
00110 
00111 
00112   blocknum BlockFor(size_type Row) const throw () 
00113         { return Row / m_Granularity; }
00114   size_type Offset(size_type Row) const throw ()
00115         { return Row % m_Granularity; }
00116   Cursor::size_type FirstRowOf(blocknum Block) const throw ()
00117         { return Block*m_Granularity; }
00118 
00119   void MoveTo(blocknum) const;
00120 
00122   Result Fetch() const;
00123 
00124   Result GetBlock(blocknum b) const
00125   {
00126     CacheMap::const_iterator i = m_Cache.find(b);
00127     if (i != m_Cache.end()) return i->second.Data();
00128 
00129     MoveTo(b);
00130     return Fetch();
00131   }
00132 
00134   size_type m_Granularity;
00135 
00136   typedef PGSTD::map<blocknum, CacheEntry> CacheMap;
00137   mutable CacheMap m_Cache;
00138 
00139   mutable Cursor m_Cursor;
00140 
00141   // Not allowed:
00142   CachedResult();
00143   CachedResult(const CachedResult &);
00144   CachedResult &operator=(const CachedResult &);
00145 };
00146 
00147 
00148 } // namespace pqxx
00149 
00150 #endif
00151 

Generated on Fri Jan 24 16:36:06 2003 for libpqxx by doxygen1.3-rc2