OTL 4.0, Example 392 (Insert/Update/Select with MySQL  LONGBLOB in stream mode, without otl_lob_stream::set_len())

This example demonstrates INSERT, UPDATE, and SELECT statements with the MySQL LONGBLOB datatype in the stream mode without otl_lob_stream::set_len() in OTL 4.0.138 and higher.

Source Code

#include <iostream>
using namespace std;

#include <stdio.h>
#define OTL_ODBC // Compile OTL 4.0/ODBC
// The following #define is required with MyODBC 3.51.11 and higher
#define OTL_ODBC_SELECT_STM_EXECUTE_BEFORE_DESCRIBE
#include <otlv4.h> // include the OTL 4.0 header file

otl_connect db; // connect object

void insert()
// insert rows into table
{otl_long_string f2(6000); // define long string variable
 otl_stream o; // defined an otl_stream variable
 o.set_lob_stream_mode(true); // set the "lob stream mode" flag
 o.open(1, // buffer size has to be set to 1 for operations with LOBs
        "insert into test_tab values(:f1<int>,:f2<raw_long>, "
        ":f3<raw_long>) ",
            // SQL statement
        db // connect object
       );
 o.set_commit(0); // setting stream "auto-commit" to "off". It is required
                  // when LOB stream mode is used.
 int i,j;
 otl_lob_stream lob; // LOB stream for reading/writing unlimited number
                     // of bytes regardless of the buffer size.
 otl_lob_stream lob2; // LOB stream for reading/writing unlimited number
                     // of bytes regardless of the buffer size.

 for(i=1;i<=20;++i){
  o<<i;
  o<<lob; // Initialize otl_lob_stream by writing it
          // into otl_stream.
  o<<lob2; // Initialize otl_lob_stream by writing it
          // into otl_stream.

  for(j=0;j<5000;++j)
   f2[j]='*';
  f2[5000]='?';
  f2.set_len(5001);

// OTL 4.0.138 and higher does not require the LOB's total length to be
// set beforehand. Instead, otl_long_string::last_piece can be used.
//  lob.set_len(5001+2123); // setting the total  size of
//                          // the LONGBLOB to be written.
  
  lob<<f2; // writing first chunk of the LONGBLOB into lob


  f2[2122]='?';
  f2.set_len(2123); // setting the size of the second chunk

  lob<<f2; // writing the second chunk of the LONGBLOB into lob
  lob.close(); // closing the otl_lob_stream

  for(j=0;j<5000;++j)
   f2[j]='*';
  f2[5000]='?';
  f2.set_len(5001);

// OTL 4.0.138 and higher does not require the LOB's total length to be
// set beforehand. Instead, otl_long_string::last_piece can be used.
//  lob2.set_len(5001+2123); // setting the total  size of
//                          // the LONGBLOB to be written.
  
  lob2<<f2; // writing first chunk of the LONGBLOB into lob

  f2[2122]='?';
  f2.set_len(2123); // setting the size of the second chunk

  lob2<<f2; // writing the second chunk of the LONGBLOB into lob
  lob2.close(); // closing the otl_lob_stream

 }

 db.commit(); // committing transaction.
}
void update()
// insert rows in table
{
 otl_long_string f2(6200); // define long string variable

 otl_stream o; // defined an otl_stream variable
 o.set_lob_stream_mode(true); // set the "lob stream mode" flag
 o.open(1, // buffer size has to be set to 1 for operations with LOBs
              "update test_tab "
              "   set f2=:f2<raw_long> "
              "where f1=:f1<int> ",
                 // SQL statement
              db // connect object
             );

  otl_lob_stream lob;

  o.set_commit(0); // setting stream "auto-commit" to "off". 


 for(int j=0;j<6000;++j){
  f2[j]='#';
 }

 f2[6000]='?';
 f2.set_len(6001);

 o<<lob; // Initialize otl_lob_stream by writing it
         // into otl_stream.
 o<<5;

// lob.set_len(6001*4); // setting the total size of of the LONGBLOB to be written
 for(int i=1;i<=4;++i)
  lob<<f2; // writing chunks of the LONGBLOB into the otl_lob_stream

 lob.close(); // closing the otl_lob_stream

 db.commit(); // committing transaction

}

void select()

 otl_long_string f2(3000); // define long string variable

 otl_stream i; // defined an otl_stream variable
 i.set_lob_stream_mode(true); // set the "lob stream mode" flag
 i.open(1, // buffer size. To read LONGBLOBs, it should be set to 1
              "select * from test_tab where f1>=:f11<int> and f1<=:f12<int>*2",
                 // SELECT statement
              db // connect object
             ); 
   // create select stream
 
 int f1;
 otl_lob_stream lob; // Stream for reading LONGBLOB
 otl_lob_stream lob2; // Stream for reading LONGBLOB
 i<<4<<4; // assigning :f11 = 4, :f12 = 4
   // SELECT automatically executes when all input variables are
   // assigned. First portion of output rows is fetched to the buffer

 while(!i.eof()){ // while not end-of-data
  i>>f1;
  cout<<"f1="<<f1<<endl;
  i>>lob; // initializing LOB stream by reading the LONGBLOB reference 
          // into the otl_lob_stream from the otl_stream.
  i>>lob2; // initializing LOB stream by reading the LONGBLOB reference 
          // into the otl_lob_stream from the otl_stream.
  int n=0;
  while(!lob.eof()){ // read while not "end-of-file" -- end of LONGBLOB 
++n;
   lob>>f2; // reading a chunk of LONGBLOB  
cout<<"   chunk #"<<n;
   cout<<", f2="<<f2[0]<<f2[f2.len()-1]<<", len="<<f2.len()<<endl;
  }
  lob.close(); // closing the otl_lob_stream.
  n=0;
  while(!lob2.eof()){ // read while not "end-of-file" -- end of LONGBLOB
   ++n;
   lob2>>f2; // reading a chunk of LONGBLOB
   cout<<"   chunk #"<<n;
   cout<<", f3="<<f2[0]<<f2[f2.len()-1]<<", len="<<f2.len()<<endl;
  }
  lob2.close(); // closing the otl_lob_stream. 
  
 }

}

int main()
{
 otl_connect::otl_initialize(); // initialize the environment
 try{

  db.rlogon("scott/tiger@mysql35"); // connect to the database

  otl_cursor::direct_exec
   (
    db,
    "drop table test_tab",
    otl_exception::disabled // disable OTL exceptions
   ); // drop table

  otl_cursor::direct_exec
   (
    db,
    "create table test_tab(f1 int, f2 longblob, f3 longblob) type=innoDB"
    );  // create table

  insert(); // insert records into table
  update(); // update records in table
  select(); // select records from table

 }

 catch(otl_exception& p){ // intercept OTL exceptions
  cerr<<p.msg<<endl; // print out error message
  cerr<<p.sqlstate<<endl; // print out SQLSTATE 
  cerr<<p.stm_text<<endl; // print out SQL that caused the error
  cerr<<p.var_info<<endl; // print out the variable that caused the error
 }

 db.logoff(); // disconnect from the database

 return 0;

}

Output

f1=4
   chunk #1, f2=**, len=3000
   chunk #2, f2=**, len=3000
   chunk #3, f2=*?, len=1124
   chunk #1, f3=**, len=3000
   chunk #2, f3=**, len=3000
   chunk #3, f3=*?, len=1124
f1=5
   chunk #1, f2=##, len=3000
   chunk #2, f2=##, len=3000
   chunk #3, f2=?#, len=3000
   chunk #4, f2=##, len=3000
   chunk #5, f2=##, len=3000
   chunk #6, f2=##, len=3000
   chunk #7, f2=##, len=3000
   chunk #8, f2=##, len=3000
   chunk #9, f2=#?, len=4
   chunk #1, f3=**, len=3000
   chunk #2, f3=**, len=3000
   chunk #3, f3=*?, len=1124
f1=6
   chunk #1, f2=**, len=3000
   chunk #2, f2=**, len=3000
   chunk #3, f2=*?, len=1124
   chunk #1, f3=**, len=3000
   chunk #2, f3=**, len=3000
   chunk #3, f3=*?, len=1124
f1=7
   chunk #1, f2=**, len=3000
   chunk #2, f2=**, len=3000
   chunk #3, f2=*?, len=1124
   chunk #1, f3=**, len=3000
   chunk #2, f3=**, len=3000
   chunk #3, f3=*?, len=1124
f1=8
   chunk #1, f2=**, len=3000
   chunk #2, f2=**, len=3000
   chunk #3, f2=*?, len=1124
   chunk #1, f3=**, len=3000
   chunk #2, f3=**, len=3000
   chunk #3, f3=*?, len=1124




Examples ContentsGo Home

Copyright © 1996-2017, Sergei Kuchin, email: skuchin@gmail.com, skuchin@gmail.com .

Permission to use, copy, modify and redistribute this document for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.