OTL 4.0, Example 380 (Insert/Update/Select,  DB2 CLOBs in stream mode, and std:strings)

This example demonstrates INSERT, UPDATE, and SELECT statements with the DB2 CLOB datatype in stream mode and std::strings.

Source Code

#include <iostream>
#include <string>
using namespace std;

#include <stdio.h>
#define OTL_DB2_CLI // Compile OTL 4.0/DB2 CLI
#define OTL_STL // enable OTL support for STL

#if (defined(__clang__) || defined(__GNUC__)) && \
(defined(OTL_CPP_14_ON) || defined(OTL_CPP_17_ON))
#include <experimental/string_view>
#define OTL_STD_STRING_VIEW_CLASS std::experimental::string_view
#elif defined(_MSC_VER) && (_MSC_VER>=1910) && defined(OTL_CPP_17_ON)
// VC++ 2017 or higher when /std=c++latest is used
#include <string_view>
#define OTL_STD_STRING_VIEW_CLASS std::string_view
#endif
#include <otlv4.h> // include the OTL 4.0 header file

otl_connect db; // connect object

void insert()
// insert rows into table
{
string f2;
 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<varchar_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.

otl_lob_stream lob; // LOB stream for reading/writing unlimited number
// of bytes regardless of the buffer size.
for(int i=1;i<=20;++i){
f2.erase();
f2.append(50000,'*');
f2 += '?';
o<<i;
o<<lob; // Initialize otl_lob_stream by writing it
// into otl_stream

lob.set_len(50001+23123); // setting the total size of
// the CLOB to be written.
// It is required for bakward compatibility

#if defined(OTL_STD_STRING_VIEW_CLASS)
OTL_STD_STRING_VIEW_CLASS f2_sv(f2.c_str(),f2.length());
lob<<f2_sv; // writing first chunk into the lob
#else
lob<<f2; // writing first chunk into the lob
#endif

f2.erase();
f2.append(23122,'*');
f2 += '?';
#if defined(OTL_STD_STRING_VIEW_CLASS)
OTL_STD_STRING_VIEW_CLASS f2_sv(f2.c_str(),f2.length());
lob<<f2_sv; // writing second chunk into the lob
#else
lob<<f2; // writing second chunk into the lob
#endif

lob.close(); // closing the otl_lob_stream
}

db.commit(); // committing transaction.
}
void update()
// insert rows in table
{
string f2;
 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<varchar_long> "
"where f1=:f1<int> ",
            // SQL statement
        db // connect object
       );
otl_lob_stream lob;
o.set_commit(0); // setting stream "auto-commit" to "off".
f2.append(6000,'#');
f2+='?';
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 CLOB to be written
for(int i=1;i<=4;++i)
lob<<f2; // writing chunks of the CLOB into the otl_lob_stream
lob.close(); // closing the otl_lob_stream
db.commit(); // committing transaction

}

void select()
{
string f2;
 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 CLOBs, 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 CLOB

lob.setStringBuffer(40000); // Set a bigger internal buffer (default is 4096 bytes)
// for reading chunks of the CLOB, before each chunk
// gets appended to the output string.
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;
i>>lob; // initializing CLOB stream by reading the CLOB reference
// into the otl_lob_stream from the otl_stream.
lob>>f2;
cout<<", f2="<<f2[0]<<f2[f2.length()-1]<<", len="<<(int)f2.length()<<endl;
lob.close(); // closing the otl_lob_stream. This step may be skipped.

}

}

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

db.rlogon("scott/tiger@db2sql"); // 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 clob(1M))"
); // 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.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, f2=*?, len=73124
f1=5, f2=#?, len=24004
f1=6, f2=*?, len=73124
f1=7, f2=*?, len=73124
f1=8, f2=*?, len=73124


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

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