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result.h

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00001 /*-------------------------------------------------------------------------
00002  *
00003  *   FILE
00004  *      pqxx/result.h
00005  *
00006  *   DESCRIPTION
00007  *      definitions for the pqxx::Result class and support classes.
00008  *   pqxx::Result represents the set of result tuples from a database query
00009  *
00010  * Copyright (c) 2001-2003, Jeroen T. Vermeulen <jtv@xs4all.nl>
00011  *
00012  *-------------------------------------------------------------------------
00013  */
00014 #ifndef PQXX_RESULT_H
00015 #define PQXX_RESULT_H
00016 
00017 #include <stdexcept>
00018 
00019 #include "pqxx/util.h"
00020 
00021 /* Methods tested in eg. self-test program test1 are marked with "//[t1]"
00022  */
00023 
00024 
00025 // TODO: Support postgres arrays
00026 
00027 namespace pqxx
00028 {
00029 
00031 
00038 class PQXX_LIBEXPORT Result
00039 {
00040 public:
00041   Result() : m_Result(0), m_Refcount(0) {}                              //[t3]
00042   Result(const Result &rhs) :                                           //[t1]
00043           m_Result(0), m_Refcount(0) { MakeRef(rhs); }
00044   ~Result() { LoseRef(); }                                              //[t1]
00045   
00046   Result &operator=(const Result &);                                    //[t10]
00047 
00048   typedef Result_size_type size_type;
00049   class Field;
00050 
00051   // TODO: Field iterators
00052  
00054 
00062   class PQXX_LIBEXPORT Tuple
00063   {
00064   public:
00065     typedef Tuple_size_type size_type;
00066     Tuple(const Result *r, Result::size_type i) : m_Home(r), m_Index(i) {}
00067     ~Tuple() {} // Yes Scott Meyers, you're absolutely right[1]
00068 
00069     inline Field operator[](size_type) const;                           //[t1]
00070     Field operator[](const char[]) const;                               //[t11]
00071     Field operator[](const PGSTD::string &s) const                      //[t11]
00072         { return operator[](s.c_str()); }
00073     Field at(size_type) const;                                          //[t10]
00074     Field at(const char[]) const;                                       //[t11]
00075     Field at(const PGSTD::string &s) const { return at(s.c_str()); }    //[t11]
00076 
00077     inline size_type size() const;                                      //[t11]
00078 
00079     Result::size_type Row() const { return m_Index; }                   //[t11]
00080 
00081     size_type ColumnNumber(const PGSTD::string &ColName) const          //[t30]
00082         { return m_Home->ColumnNumber(ColName); }
00083 
00084     size_type ColumnNumber(const char ColName[]) const                  //[t30]
00085         { return m_Home->ColumnNumber(ColName); }
00086 
00087   protected:
00088     const Result *m_Home;
00089     Result::size_type m_Index;
00090 
00091     // Not allowed:
00092     Tuple();
00093   };
00094 
00095 
00097 
00100   class PQXX_LIBEXPORT Field : private Tuple
00101   {
00102   public:
00103     typedef size_t size_type;
00104 
00106 
00110     Field(const Tuple &R, Tuple::size_type C) : Tuple(R), m_Col(C) {}   //[t1]
00111 
00113 
00118     const char *c_str() const {return m_Home->GetValue(m_Index,m_Col);} //[t2]
00119 
00121     inline const char *Name() const;                                    //[t11]
00122 
00124     template<typename T> bool to(T &Obj) const                          //[t1]
00125     {
00126       if (is_null())
00127         return false;
00128 
00129       try
00130       {
00131         FromString(c_str(), Obj);
00132       }
00133       catch (const PGSTD::exception &e)
00134       {
00135         throw PGSTD::runtime_error("Error reading field " + 
00136                                    PGSTD::string(Name()) +
00137                                    ": " +
00138                                    e.what());
00139       }
00140       return true;
00141     }
00142 
00143 
00144 #ifdef NO_PARTIAL_CLASS_TEMPLATE_SPECIALISATION
00145 
00146     template<> bool to<PGSTD::string>(PGSTD::string &Obj) const;
00147 
00149 
00152     template<> bool to<const char *>(const char *&Obj) const;
00153 #endif
00154 
00155 
00157     template<typename T> bool to(T &Obj, const T &Default) const        //[t12]
00158     {
00159       const bool NotNull = to(Obj);
00160       if (!NotNull)
00161         Obj = Default;
00162       return NotNull;
00163     }
00164 
00165     bool is_null() const { return m_Home->GetIsNull(m_Index,m_Col); }   //[t12]
00166 
00167     size_type size() const { return m_Home->GetLength(m_Index,m_Col); } //[t11]
00168 
00169   private:
00170 
00171     Tuple::size_type m_Col;
00172   };
00173 
00174 
00176 
00180   class PQXX_LIBEXPORT const_iterator : 
00181     public PGSTD::iterator<PGSTD::random_access_iterator_tag, 
00182                          const Tuple,
00183                          Result::size_type>, 
00184     public Tuple
00185   {
00186   public:
00187     const_iterator() : Tuple(0,0) {}
00188 
00195     pointer operator->()  const { return this; }                        //[t12]
00196     reference operator*() const { return *operator->(); }               //[t12]
00197 
00198     const_iterator operator++(int);                                     //[t12]
00199     const_iterator &operator++() { ++m_Index; return *this; }           //[t1]
00200     const_iterator operator--(int);                                     //[t12]
00201     const_iterator &operator--() { --m_Index; return *this; }           //[t12]
00202 
00203     const_iterator &operator+=(difference_type i)                       //[t12]
00204         { m_Index+=i; return *this; }
00205     const_iterator &operator-=(difference_type i)                       //[t12]
00206         { m_Index-=i; return *this; }
00207 
00208     bool operator==(const const_iterator &i) const                      //[t12]
00209         {return m_Index==i.m_Index;}
00210     bool operator!=(const const_iterator &i) const                      //[t12]
00211         {return m_Index!=i.m_Index;}
00212     bool operator<(const const_iterator &i) const                       //[t12]
00213          {return m_Index<i.m_Index;}
00214     bool operator<=(const const_iterator &i) const                      //[t12]
00215         {return m_Index<=i.m_Index;}
00216     bool operator>(const const_iterator &i) const                       //[t12]
00217         {return m_Index>i.m_Index;}
00218     bool operator>=(const const_iterator &i) const                      //[t12]
00219         {return m_Index>=i.m_Index;}
00220 
00221     inline const_iterator operator+(difference_type o) const;           //[t12]
00222 
00223     friend const_iterator operator+(difference_type o, 
00224                                     const_iterator i);                  //[t12]
00225 
00226     inline const_iterator operator-(difference_type o) const;           //[t12]
00227 
00228     inline difference_type operator-(const_iterator i) const;           //[t12]
00229 
00230     Result::size_type num() const { return Row(); }                     //[t1]
00231 
00232   private:
00233     friend class Result;
00234     const_iterator(const Result *r, Result::size_type i) : Tuple(r, i) {}
00235   };
00236 
00237   const_iterator begin() const { return const_iterator(this, 0); }      //[t1]
00238   inline const_iterator end() const;                                    //[t1]
00239   // TODO: Reverse iterators
00240 
00241   size_type size() const { return m_Result ? PQntuples(m_Result) : 0; } //[t2]
00242   bool empty() const { return !m_Result || !PQntuples(m_Result); }      //[t11]
00243   size_type capacity() const { return size(); }                         //[t20]
00244 
00245   const Tuple operator[](size_type i) const { return Tuple(this, i); }  //[t2]
00246   const Tuple at(size_type) const;                                      //[t10]
00247 
00248   void clear() { LoseRef(); }                                           //[t20]
00249 
00250   Tuple::size_type Columns() const { return PQnfields(m_Result); }      //[t11]
00251 
00253   Tuple::size_type ColumnNumber(const char Name[]) const                //[t11]
00254         {return PQfnumber(m_Result,Name);}
00256   Tuple::size_type ColumnNumber(const std::string &Name) const          //[t11]
00257         {return ColumnNumber(Name.c_str());}
00258   const char *ColumnName(Tuple::size_type Number) const                 //[t11]
00259         {return PQfname(m_Result,Number);}
00260 
00262 
00263   Oid InsertedOid() const { return PQoidValue(m_Result); }              //[t13]
00264 
00266   /*** Returns zero for all other commands. */
00267   size_type AffectedRows() const;                                       //[t7]
00268 
00269 private:
00270   PGresult *m_Result;
00271   mutable int *m_Refcount;
00272 
00273   friend class Result::Field;
00274   const char *GetValue(size_type Row, Tuple::size_type Col) const;
00275   bool GetIsNull(size_type Row, Tuple::size_type Col) const;
00276   Field::size_type GetLength(size_type Row, Tuple::size_type Col) const;
00277 
00278   friend class ConnectionItf;
00279   explicit Result(PGresult *rhs) : m_Result(rhs), m_Refcount(0) {MakeRef(rhs);}
00280   Result &operator=(PGresult *);
00281   bool operator!() const throw () { return !m_Result; }
00282   operator bool() const throw () { return m_Result != 0; }
00283   void CheckStatus(const PGSTD::string &Query) const;
00284 
00285   friend class Cursor;
00286   const char *CmdStatus() const throw () { return PQcmdStatus(m_Result); }
00287 
00288 
00289   void MakeRef(PGresult *);
00290   void MakeRef(const Result &);
00291   void LoseRef() throw ();
00292 };
00293 
00294 
00295 inline Result::Field 
00296 Result::Tuple::operator[](Result::Tuple::size_type i) const 
00297 { 
00298   return Field(*this, i); 
00299 }
00300 
00301 inline Result::Tuple::size_type Result::Tuple::size() const 
00302 { 
00303   return m_Home->Columns(); 
00304 }
00305 
00306 inline const char *Result::Field::Name() const 
00307 { 
00308   return m_Home->ColumnName(m_Col); 
00309 }
00310 
00312 template<> 
00313 inline bool Result::Field::to<PGSTD::string>(PGSTD::string &Obj) const
00314 {
00315   if (is_null()) return false;
00316   Obj = c_str();
00317   return true;
00318 }
00319 
00321 
00324 template<> 
00325 inline bool Result::Field::to<const char *>(const char *&Obj) const
00326 {
00327   if (is_null()) return false;
00328   Obj = c_str();
00329   return true;
00330 }
00331 
00332 
00333 inline Result::const_iterator 
00334 Result::const_iterator::operator+(difference_type o) const
00335 {
00336   return const_iterator(m_Home, m_Index + o);
00337 }
00338 
00339 inline Result::const_iterator 
00340 operator+(Result::const_iterator::difference_type o, 
00341           Result::const_iterator i)
00342 {
00343   return i + o;
00344 }
00345 
00346 inline Result::const_iterator 
00347 Result::const_iterator::operator-(difference_type o) const
00348 {
00349   return const_iterator(m_Home, m_Index - o);
00350 }
00351 
00352 inline Result::const_iterator::difference_type 
00353 Result::const_iterator::operator-(const_iterator i) const
00354 { 
00355   return num()-i.num(); 
00356 }
00357 
00358 inline Result::const_iterator Result::end() const 
00359 { 
00360   return const_iterator(this, size()); 
00361 }
00362 
00363 } // namespace pqxx
00364 
00365 
00367 
00384 template<typename STREAM>
00385 inline STREAM &operator<<(STREAM &S, const pqxx::Result::Field &F)      //[t46]
00386 {
00387   S << F.c_str();
00388   return S;
00389 }
00390 
00391 
00392 
00393 /* 
00394 [1] Scott Meyers, in one of his essential books, "Effective C++" and "More 
00395 Effective C++", points out that it is good style to have any class containing 
00396 a member of pointer type define its own destructor--just to show that it knows
00397 what it is doing.  This helps prevent nasty memory leak / double deletion bugs
00398 typically resulting from programmers' omission to deal with such issues in
00399 their destructors.
00400 
00401 The -Weffc++ option in gcc generates warnings for noncompliance with Scott's
00402 style guidelines, and hence necessitates the definition of this destructor,\
00403 trivial as it may be.
00404 
00405 [2] IIRC Alex Stepanov, the inventor of the STL, once remarked that having
00406 this as standard behaviour for pointers would be useful in some algorithms.
00407 So even if this makes me look foolish, I would seem to be in distinguished 
00408 company.
00409 */
00410 
00411 #endif
00412 

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