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Archived:Using Symbian SQL API with data streams

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Revision as of 11:03, 2 May 2008


ID   Creation date April 24, 2008
Platform S60 3rd Edition, FP2 Tested on devices Nokia 6220 Classic
Category Symbian C++ Subcategory Files/Data


Keywords (APIs, classes, methods, functions): RSqlDatabase,RSqlStatement,RSqlParamWriteStream, RSqlColumnReadStream, RSqlParamWriteStream::BindInt(), RSqlParamWriteStream::BindText(), RSqlParamWriteStream::BindBinary(), RSqlParamWriteStream::Close(), RSqlColumnReadStream::ColumnText() RSqlColumnReadStream::ColumnBinary() RSqlColumnReadStream::ColumnClose()

Overview

This snippet shows how to use two classes that support the streaming functionality with SQL API. Data streams can be used to write to a database by declaring an RSqlParamWriteStream object and call one of its Bind() methods e.g. BindText(). Reading data from a database to a data stream is possible by declaring an RSqlColumnReadStream object and call one of its Column() methods e.g. ColumnBinary().

This snippet can be self-signed.

MMP file

The following libraries are required:

LIBRARY  euser.lib
LIBRARY sqldb.lib
LIBRARY estor.lib //RSqlColumnReadStream, RSqlParamWriteStream


Source file

#include <e32base.h>
#include <SqlDb.h>
 
void ReadAndWriteStreamsL()
{
 
_LIT(KStreamsDbName, "\\streams.db");
 
RSqlDatabase database;
TInt error = database.Create(KStreamsDbName);
 
// == Writing from a data stream ==
 
if(error == KErrNone)
{
CleanupClosePushL(database);
 
// Create a table
_LIT(KSqlCreateTableStreams, "CREATE TABLE STREAMS(ID INTEGER, STREAM1 TEXT,
STREAM2 BLOB);"
);
User::LeaveIfError(database.Exec(KSqlCreateTableStreams));
 
_LIT(KSqlInsertIntoTableStreams, "INSERT INTO STREAMS(ID, STREAM1, STREAM2)
VALUES(:Val1, :Val2, :Val3)"
);
 
RSqlStatement sqlInsertIntoStreamsStatement;
sqlInsertIntoStreamsStatement.Prepare(database, KSqlInsertIntoTableStreams);
CleanupClosePushL(sqlInsertIntoStreamsStatement);
 
TInt paramIndex1 = sqlInsertIntoStreamsStatement.ParameterIndex(_L(":Val1"));
TInt paramIndex2 = sqlInsertIntoStreamsStatement.ParameterIndex(_L(":Val2"));
TInt paramIndex3 = sqlInsertIntoStreamsStatement.ParameterIndex(_L(":Val3"));
 
for(TInt id=1; id<10; id++)
{
//Set value into column ID
User::LeaveIfError(sqlInsertIntoStreamsStatement.BindInt(paramIndex1, id));
 
RSqlParamWriteStream stream1;
RSqlParamWriteStream stream2;
CleanupClosePushL(stream1);
CleanupClosePushL(stream2);
 
User::LeaveIfError(stream1.BindText(sqlInsertIntoStreamsStatement,
paramIndex2));
 
//Generate some text data into column STREAM2
TChar ch = '0' + id;
TBuf<500> idBuf;
idBuf.Fill(ch,500);
stream1.WriteL(idBuf);
 
User::LeaveIfError(stream2.BindBinary(sqlInsertIntoStreamsStatement,
paramIndex3));
 
//Generate some binary data into column STREAM2
TUint8 startValue = '0' + id;
TUint8 endValue = startValue + 100;
 
for(; startValue<endValue; startValue++)
{
stream2 << static_cast <TUint8> (startValue);
}
stream2.CommitL();
 
User::LeaveIfError(sqlInsertIntoStreamsStatement.Exec());
User::LeaveIfError(sqlInsertIntoStreamsStatement.Reset());
 
CleanupStack::PopAndDestroy(2); //stream2, stream1
}
 
CleanupStack::PopAndDestroy(2); //sqlInsertIntoStreamsStatement, database
}
else
{
//open database failed
}
 
// == Reading to a data stream ==
error = database.Open(KStreamsDbName);
 
if (error == KErrNone)
{
CleanupClosePushL(database);
 
RSqlStatement sqlSelectFromStreamsTableStatement;
 
_LIT(KSqlSelectFromStreamsTable, "SELECT * FROM STREAMS");
TInt ret = sqlSelectFromStreamsTableStatement.Prepare(database,
KSqlSelectFromStreamsTable);
 
if(ret == KErrNone)
{
CleanupClosePushL(sqlSelectFromStreamsTableStatement);
 
TInt columnIndex1 = sqlSelectFromStreamsTableStatement.ColumnIndex(_L("STREAM1"));
TInt columnIndex2 = sqlSelectFromStreamsTableStatement.ColumnIndex(_L("STREAM2"));
 
TInt err = KErrNone;
 
while((err = sqlSelectFromStreamsTableStatement.Next()) == KSqlAtRow)
{
RSqlColumnReadStream stream1;
RSqlColumnReadStream stream2;
CleanupClosePushL(stream1);
CleanupClosePushL(stream2);
 
//Get data from text column STREAM1
User::LeaveIfError(stream1.ColumnText(sqlSelectFromStreamsTableStatement,
columnIndex1));
TInt size1 = sqlSelectFromStreamsTableStatement.ColumnSize(columnIndex1);
RBuf buf;
buf.CreateL(size1);
CleanupClosePushL(buf);
 
stream1.ReadL(buf,size1);
//do something with the data...
 
//Get data from binary column STREAM2
User::LeaveIfError(stream2.ColumnBinary(sqlSelectFromStreamsTableStatement,
columnIndex2));
TInt size2 = sqlSelectFromStreamsTableStatement.ColumnSize(columnIndex2);
HBufC8* buf2 = HBufC8::NewLC(size2);
TPtr8 buf2Ptr = buf2->Des();
 
stream2.ReadL(buf2Ptr,size2);
//do something with the data...
CleanupStack::PopAndDestroy(4); //buf2, buf, stream2, stream1
}
if(err == KSqlAtEnd)
{
// OK - no more records
}
else
{
// process the error
}
 
CleanupStack::PopAndDestroy(2); //sqlSelectFromStreamsTableStatement, database
}
else
{
//open database failed
}
}

Postconditions

The example database streams.db is created and the test rows are inserted into tables using RSqlParamWriteStream streams. After that RSqlColumnReadStream streams are used to fetch the test data.

See also

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