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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   protected:
00082     const Result *m_Home;
00083     Result::size_type m_Index;
00084 
00085     // Not allowed:
00086     Tuple();
00087   };
00088 
00089 
00091 
00094   class PQXX_LIBEXPORT Field : private Tuple
00095   {
00096   public:
00097     typedef size_t size_type;
00098 
00100 
00104     Field(const Tuple &R, Tuple::size_type C) : Tuple(R), m_Col(C) {}   //[t1]
00105 
00107 
00112     const char *c_str() const {return m_Home->GetValue(m_Index,m_Col);} //[t2]
00113 
00115     inline const char *Name() const;                                    //[t11]
00116 
00118     template<typename T> bool to(T &Obj) const                          //[t1]
00119     {
00120       if (is_null())
00121         return false;
00122 
00123       try
00124       {
00125         FromString(c_str(), Obj);
00126       }
00127       catch (const PGSTD::exception &e)
00128       {
00129         throw PGSTD::runtime_error("Error reading field " + 
00130                                    PGSTD::string(Name()) +
00131                                    ": " +
00132                                    e.what());
00133       }
00134       return true;
00135     }
00136 
00137 
00138 #ifdef NO_PARTIAL_CLASS_TEMPLATE_SPECIALISATION
00139 
00140     template<> bool to<PGSTD::string>(PGSTD::string &Obj) const;
00141 
00143 
00146     template<> bool to<const char *>(const char *&Obj) const;
00147 #endif
00148 
00149 
00151     template<typename T> bool to(T &Obj, const T &Default) const        //[t12]
00152     {
00153       const bool NotNull = to(Obj);
00154       if (!NotNull)
00155         Obj = Default;
00156       return NotNull;
00157     }
00158 
00159     bool is_null() const { return m_Home->GetIsNull(m_Index,m_Col); }   //[t12]
00160 
00161     int size() const { return m_Home->GetLength(m_Index,m_Col); }       //[t11]
00162 
00163   private:
00164 
00165     Tuple::size_type m_Col;
00166   };
00167 
00168 
00170 
00174   class PQXX_LIBEXPORT const_iterator : 
00175     public PGSTD::iterator<PGSTD::random_access_iterator_tag, 
00176                          const Tuple,
00177                          Result::size_type>, 
00178     public Tuple
00179   {
00180   public:
00181     const_iterator() : Tuple(0,0) {}
00182 
00189     pointer operator->()  const { return this; }                        //[t12]
00190     reference operator*() const { return *operator->(); }               //[t12]
00191 
00192     const_iterator operator++(int);                                     //[t12]
00193     const_iterator &operator++() { ++m_Index; return *this; }           //[t1]
00194     const_iterator operator--(int);                                     //[t12]
00195     const_iterator &operator--() { --m_Index; return *this; }           //[t12]
00196 
00197     const_iterator &operator+=(difference_type i)                       //[t12]
00198         { m_Index+=i; return *this; }
00199     const_iterator &operator-=(difference_type i)                       //[t12]
00200         { m_Index-=i; return *this; }
00201 
00202     bool operator==(const const_iterator &i) const                      //[t12]
00203         {return m_Index==i.m_Index;}
00204     bool operator!=(const const_iterator &i) const                      //[t12]
00205         {return m_Index!=i.m_Index;}
00206     bool operator<(const const_iterator &i) const                       //[t12]
00207          {return m_Index<i.m_Index;}
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 
00215     inline const_iterator operator+(difference_type o) const;           //[t12]
00216 
00217     friend const_iterator operator+(difference_type o, 
00218                                     const_iterator i);                  //[t12]
00219 
00220     inline const_iterator operator-(difference_type o) const;           //[t12]
00221 
00222     inline difference_type operator-(const_iterator i) const;           //[t12]
00223 
00224     Result::size_type num() const { return Row(); }                     //[t1]
00225 
00226   private:
00227     friend class Result;
00228     const_iterator(const Result *r, Result::size_type i) : Tuple(r, i) {}
00229   };
00230 
00231   const_iterator begin() const { return const_iterator(this, 0); }      //[t1]
00232   inline const_iterator end() const;                                    //[t1]
00233   // TODO: Reverse iterators
00234 
00235   size_type size() const { return m_Result ? PQntuples(m_Result) : 0; } //[t2]
00236   bool empty() const { return !m_Result || !PQntuples(m_Result); }      //[t11]
00237   size_type capacity() const { return size(); }                         //[t20]
00238 
00239   const Tuple operator[](size_type i) const { return Tuple(this, i); }  //[t2]
00240   const Tuple at(size_type) const;                                      //[t10]
00241 
00242   void clear() { LoseRef(); }                                           //[t20]
00243 
00244   Tuple::size_type Columns() const { return PQnfields(m_Result); }      //[t11]
00245 
00247   Tuple::size_type ColumnNumber(const char Name[]) const                //[t11]
00248         {return PQfnumber(m_Result,Name);}
00250   Tuple::size_type ColumnNumber(const std::string &Name) const          //[t11]
00251         {return ColumnNumber(Name.c_str());}
00252   const char *ColumnName(Tuple::size_type Number) const                 //[t11]
00253         {return PQfname(m_Result,Number);}
00254 
00256 
00257   Oid InsertedOid() const { return PQoidValue(m_Result); }              //[t13]
00258 
00260   /*** Returns zero for all other commands. */
00261   size_type AffectedRows() const;                                       //[t7]
00262 
00263 private:
00264   PGresult *m_Result;
00265   mutable int *m_Refcount;
00266 
00267   friend class Result::Field;
00268   const char *GetValue(size_type Row, Tuple::size_type Col) const;
00269   bool GetIsNull(size_type Row, Tuple::size_type Col) const;
00270   Field::size_type GetLength(size_type Row, Tuple::size_type Col) const;
00271 
00272   friend class ConnectionItf;
00273   explicit Result(PGresult *rhs) : m_Result(rhs), m_Refcount(0) {MakeRef(rhs);}
00274   Result &operator=(PGresult *);
00275   bool operator!() const throw () { return !m_Result; }
00276   operator bool() const throw () { return m_Result != 0; }
00277   void CheckStatus(const PGSTD::string &Query) const;
00278 
00279   friend class Cursor;
00280   const char *CmdStatus() const throw () { return PQcmdStatus(m_Result); }
00281 
00282 
00283   void MakeRef(PGresult *);
00284   void MakeRef(const Result &);
00285   void LoseRef() throw ();
00286 };
00287 
00288 
00289 inline Result::Field 
00290 Result::Tuple::operator[](Result::Tuple::size_type i) const 
00291 { 
00292   return Field(*this, i); 
00293 }
00294 
00295 inline Result::Tuple::size_type Result::Tuple::size() const 
00296 { 
00297   return m_Home->Columns(); 
00298 }
00299 
00300 inline const char *Result::Field::Name() const 
00301 { 
00302   return m_Home->ColumnName(m_Col); 
00303 }
00304 
00306 template<> 
00307 inline bool Result::Field::to<PGSTD::string>(PGSTD::string &Obj) const
00308 {
00309   if (is_null()) return false;
00310   Obj = c_str();
00311   return true;
00312 }
00313 
00315 
00318 template<> 
00319 inline bool Result::Field::to<const char *>(const char *&Obj) const
00320 {
00321   if (is_null()) return false;
00322   Obj = c_str();
00323   return true;
00324 }
00325 
00326 
00327 inline Result::const_iterator 
00328 Result::const_iterator::operator+(difference_type o) const
00329 {
00330   return const_iterator(m_Home, m_Index + o);
00331 }
00332 
00333 inline Result::const_iterator 
00334 operator+(Result::const_iterator::difference_type o, 
00335           Result::const_iterator i)
00336 {
00337   return i + o;
00338 }
00339 
00340 inline Result::const_iterator 
00341 Result::const_iterator::operator-(difference_type o) const
00342 {
00343   return const_iterator(m_Home, m_Index - o);
00344 }
00345 
00346 inline Result::const_iterator::difference_type 
00347 Result::const_iterator::operator-(const_iterator i) const
00348 { 
00349   return num()-i.num(); 
00350 }
00351 
00352 inline Result::const_iterator Result::end() const 
00353 { 
00354   return const_iterator(this, size()); 
00355 }
00356 
00357 } // namespace pqxx
00358 
00359 
00361 
00378 template<typename STREAM>
00379 inline STREAM &operator<<(STREAM &S, const pqxx::Result::Field &F)      //[t46]
00380 {
00381   S << F.c_str();
00382   return S;
00383 }
00384 
00385 
00386 
00387 /* 
00388 [1] Scott Meyers, in one of his essential books, "Effective C++" and "More 
00389 Effective C++", points out that it is good style to have any class containing 
00390 a member of pointer type define its own destructor--just to show that it knows
00391 what it is doing.  This helps prevent nasty memory leak / double deletion bugs
00392 typically resulting from programmers' omission to deal with such issues in
00393 their destructors.
00394 
00395 The -Weffc++ option in gcc generates warnings for noncompliance with Scott's
00396 style guidelines, and hence necessitates the definition of this destructor,\
00397 trivial as it may be.
00398 
00399 [2] IIRC Alex Stepanov, the inventor of the STL, once remarked that having
00400 this as standard behaviour for pointers would be useful in some algorithms.
00401 So even if this makes me look foolish, I would seem to be in distinguished 
00402 company.
00403 */
00404 
00405 #endif
00406 

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