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/*
* Copyright (C) 2014 Tommi Maekitalo
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* As a special exception, you may use this file as part of a free
* software library without restriction. Specifically, if other files
* instantiate templates or use macros or inline functions from this
* file, or you compile this file and link it with other files to
* produce an executable, this file does not by itself cause the
* resulting executable to be covered by the GNU General Public
* License. This exception does not however invalidate any other
* reasons why the executable file might be covered by the GNU Library
* General Public License.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/*
This demonstrates the various ways to read data from a database with tntdb.
*/
#include <iostream>
#include <cxxtools/log.h>
#include <tntdb/connect.h>
#include <tntdb/statement.h>
#include <tntdb/result.h>
#include <tntdb/row.h>
#include <tntdb/value.h>
int main(int argc, char* argv[])
{
try
{
log_init(); // logging should be initialized always
if (argc < 2)
{
std::cerr << "Usage: " << argv[0] << " dburl" << std::endl;
return -1;
}
const std::string database = argv[1];
tntdb::Connection db = tntdb::connect(database);
// selecting a single value
unsigned count;
db.selectValue("select count(*)"
" from foo") // returns a tntdb::Value
.get(count); // extracts unsigned value from tntdb::Value
// selecting multiple values
unsigned max, min;
tntdb::Row row = db.selectRow("select max(a) as max, min(a) as min"
" from foo");
row["max"].get(max);
row["min"].get(min);
// reading multiple values from a row with tntdb::RowReader
db.selectRow("select max(a), min(a)"
" from foo") // returns a tntdb::Row
.get(max) // extracts unsigned and returns a tntdb::RowReader
.get(min);
// reading a result set
// Note that a tntdb::Result helds the whole result in memory, which may not be what you want.
// Use tntdb::Statement to fetch step by step.
tntdb::Result result = db.select("select a, b"
" from foo");
for (tntdb::Result::const_iterator it = result.begin(); it != result.end(); ++it)
{
tntdb::Row r = *it; // dereferencing returns a tntdb::Row
unsigned a;
std::string b;
bool a_isnull = r["a"].get(a); // get returns a boolean wether the value was null
bool b_isnull = r["b"].get(b);
// as an alternative we can use index
r[0].get(a);
r[1].get(b);
// or again tntdb::RowReader
r.get(a)
.get(b);
// a or b may be null:
r.get(a, a_isnull)
.get(b, b_isnull);
}
// using tntdb::Statement
// fetching value
db.prepare("select count(*)"
" from foo"
" where a > :a") // returns tntdb::Statement
.set("a", 42) // sets :a to a value
.selectValue() // returns a tntdb::Value
.get(count); // extracts unsigned value from tntdb::Value
// fetching multiple values
row = db.prepare("select max(a) as max, min(a) as min"
" from foo"
" where a > :a")
.set("a", 42)
.selectRow();
row["max"].get(max);
row["min"].get(min);
// reading multiple values from a row with tntdb::RowReader
db.prepare("select max(a), min(a)"
" from foo"
" where a > :a")
.set("a", 42) // sets :a to a value
.selectRow()
.get(max) // extracts unsigned and returns a tntdb::RowReader
.get(min);
// reading data step by step
tntdb::Statement stmt = db.prepare("select a, b"
" from foo"
" where a > :a");
stmt.set("a", 42);
for (tntdb::Statement::const_iterator it = stmt.begin(); it != stmt.end(); ++it)
{
tntdb::Row r = *it; // dereferencing returns a tntdb::Row
unsigned a;
std::string b;
// the row can be read just like in tntdb::Result
bool a_isnull = r["a"].get(a); // get returns a boolean wether the value was null
bool b_isnull = r["b"].get(b);
// the iterator can also return a RowReader
it.get(a, a_isnull)
.get(b, b_isnull);
}
}
catch (const std::exception& e)
{
std::cerr << e.what() << std::endl;
}
}
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