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Revision as of 04:53, 10 May 2012 by hamishwillee (Talk | contribs)

Archived:Using Symbian SQL API with SQL statements which return data

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Archived.pngArchived: This article is archived because it is not considered relevant for third-party developers creating commercial solutions today. If you think this article is still relevant, let us know by adding the template {{ReviewForRemovalFromArchive|user=~~~~|write your reason here}}.

Article Metadata
Tested with
Devices(s): Nokia 6220 Classic
Compatibility
Platform(s): S60 3rd Edition, FP2
S60 3rd Edition FP2
Article
Keywords: RSqlDatabase, RSqlStatement, RSqlDatabase::Open(), RSqlDatabase::Close(), RSqlStatement::Prepare(), RSqlStatement::ParameterIndex(), RSqlStatement::BindInt(), RSqlStatement::ColumnIndex(), RSqlStatement::ColumnTextL(), RSqlStatement::ColumnInt(), RSqlStatement::ColumnSize(), RSqlStatement::Next(), RSqlStatement::Close()
Created: aknyman (24 Apr 2008)
Last edited: hamishwillee (10 May 2012)

Contents

Overview

The RSqlStatement class provides functionality to execute all types of SQL statements when using the SQL API. RSqlStatement encapsulates an SQL statement and the data that it returns. RSqlStatement statements can be executed with the methods Exec() and Next(). The method Exec() is used when the statement does not return any data and Next() when the statement returns data. This snippet gives some examples on how to use the Next() method.

Statements use so-called placeholders (:) in descriptors to mark positions where dynamic data is inserted at runtime. The user can bind the actual data to placeholders with different Bind() methods, such as BindText(). It is good practise to resolve the placeholder index with the RSqlStatement::ParameterIndex() method, and not use hardcoded values.

The method ColumnSize() helps when the size of returned data is unknown and the user wants to copy it to the allocated buffer. Data can be copied into the user-allocated buffer with Column() methods, such as ColumnText().

This snippet can be self-signed.


MMP file

The following libraries are required:

LIBRARY euser.lib
LIBRARY sqldb.lib


The following capabilities are needed to test the example secure database:

CAPABILITY ReadUserData
CAPABILITY WriteUserData

Preconditions

Databases nonsecure.db and [UID3]secure.db need to be created before executing this code snippet. See Using SQL API for creating non-secure and secure databases on Symbian.


Source file

#include <e32base.h>
#include <SqlDb.h>
 
void NextStatementsL()
{
RSqlDatabase database;
_LIT(KNonSecureDbName, "\\nonsecure.db");
_LIT(KSecureDbName, "[E80000AF]secure.db");
 
//== Retrieving numeric data
TInt error = database.Open(KNonSecureDbName);
 
if (error == KErrNone)
{
CleanupClosePushL(database);
 
RSqlStatement sqlSelectFromMoviesTableStatement;
_LIT(KSqlSelectFromMoviesTable, "SELECT * FROM MOVIES WHERE YEAR < :Val1");
TInt ret = sqlSelectFromMoviesTableStatement.Prepare(database, KSqlSelectFromMoviesTable);
 
if(ret == KErrNone)
{
CleanupClosePushL(sqlSelectFromMoviesTableStatement);
TInt paramIndex1 = sqlSelectFromMoviesTableStatement.ParameterIndex(_L(":Val1"));
 
User::LeaveIfError(sqlSelectFromMoviesTableStatement.BindInt(paramIndex1, 2000));
 
TInt columnIndex = sqlSelectFromMoviesTableStatement.ColumnIndex(_L("ID"));
TInt err = KErrNone;
 
while((err = sqlSelectFromMoviesTableStatement.Next()) == KSqlAtRow)
{
TInt id = sqlSelectFromMoviesTableStatement.ColumnInt(columnIndex);
//Do something with id (movie released before year 2000 )
}
if(err == KSqlAtEnd)
{
//OK - no more records
}
else
{
//process the error
}
 
CleanupStack::PopAndDestroy(1); //sqlSelectFromMoviesTableStatement
}
else
{
//prepare sql statement failed
}
CleanupStack::PopAndDestroy(1); //database
}
else
{
//open database failed
}
 
//== Retrieving text data
 
error = database.Open(KSecureDbName);
 
if (error == KErrNone)
{
CleanupClosePushL(database);
 
RSqlStatement sqlSelectFromBooksTableStatement;
_LIT(KSqlSelectFromBooksTable, "SELECT * FROM BOOKS");
TInt ret = sqlSelectFromBooksTableStatement.Prepare(database, KSqlSelectFromBooksTable);
 
if(ret == KErrNone)
{
CleanupClosePushL(sqlSelectFromBooksTableStatement);
 
TInt columnIndex1 = sqlSelectFromBooksTableStatement.ColumnIndex(_L("TITLE"));
TInt columnIndex2 = sqlSelectFromBooksTableStatement.ColumnIndex(_L("AUTHOR"));
 
TInt err = KErrNone;
 
while((err = sqlSelectFromBooksTableStatement.Next()) == KSqlAtRow)
{
// access data with copying:
RBuf title;
TInt titleSize = sqlSelectFromBooksTableStatement.ColumnSize(columnIndex1);
title.CreateL(titleSize);
CleanupClosePushL(title);
User::LeaveIfError(sqlSelectFromBooksTableStatement.ColumnText(columnIndex1,title));
//do something with the data...
CleanupStack::PopAndDestroy(1); //title
 
// ...or access data without copying:
TPtrC author = sqlSelectFromBooksTableStatement.ColumnTextL(columnIndex2);
//do something with the data...
}
if(err == KSqlAtEnd)
{
//OK - no more records
}
else
{
//process the error
}
CleanupStack::PopAndDestroy(1); //sqlSelectFromMoviesTableStatement
}
else
{
//prepare sql statement failed
}
CleanupStack::PopAndDestroy(1); //database
}
else
{
//open database failed
}
 
}

Postconditions

The RSqlStatement class is used to fetch data from the nonsecure.db and [UID3]secure.db databases. The first statement is used to retrieve numeric data and the second one is used to retrieve textual data.

See also

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