SQL Server (OLEDB) Guide

SQLAPI++ allows to seamlessly work with a variety of SQL database servers. It provides unified API to access any database, keeping your code portable. But each server has some specific features which a developer has to know in order to leverage server's unique features and avoid potential errors.

For complete information on using SQLAPI++ check out Getting Started and Documentation. This guide covers specific information related to working with SQL Server (OLEDB) server using SQLAPI++ library in the following areas:

• Connecting to a database
• Transaction isolation levels
• Working with Long or Lob (CLob, BLob) data
• Returning output parameters
• Cancelling queries
• Connection, command, parameter and field options
• Using native API
• Getting native connection related handles
• Getting native command related handles
• Error handling

Connecting to a database

To connect to a database you need to initialize a connection object. A connection object is represented by SAConnection class.

Starting from version 4.0.3 SQLAPI++ library uses ODBC as the default API when working with SQL Server. If you want to use OLE DB, you should set "UseAPI" connection option before specifying SQL Server client or connecting to database:

SAConnection con;
con.setOption(_TSA("UseAPI")) = _TSA("OLEDB");

If the library cannot find OLEDB interface it throws an exception.

After the connection is created you need to call SAConnection::Connect method to establish connection with SQL Server server:

void Connect(
    const SAString &sDBString,
    const SAString &sUserID, 
    const SAString &sPassword, 
    SAClient_t eSAClient = SA_Client_NotSpecified);

Parameters

sDBString

[<server_name>@][<database_name>][;<driver_connection_option_list>]

• <server_name> - connects to a specified server. If it's omitted SQLAPI++ tries to connect to default local server instance
• <database_name> - connects to a database with the specified name. If it's omitted SQLAPI++ tries to connect to default database
• <driver_connection_parameters_list> - SQL Server OLEDB driver specific parameters list

To connect to a named instance of SQL Server use <server name\instance name> instead of <server_name> (use double back slash in C++ constants, for example "MyServer\\SQLEXPRESS@pubs").

• lpc:<servername>[\instancename] - using shared memory
• tcp:<servername>[\<instancename>],<port> or tcp:<IPAddress>[\<instancename>],<port> - using TCP/IP
• np:\<computer_name>\pipe\<pipename> or np:\<IPAddress>\pipe\<pipename> - using named pipes
• via:<servername>[\instancename],<nic_number>:<port> - using VIA

To open Compact Edition database file use <file path> connection string (see connection option also).

sUserID

A string containing a user name to use when establishing the connection.

If sUserID parameter is empty, SQLAPI++ library requests a secure, or trusted, connection to SQL Server.

sPassword

A string containing a password to use when establishing the connection.

eSAClient

• SA_SQLServer_Client – SQL Server client
• SA_Client_NotSpecified – used by default if eSAClient parameter is omitted. You can use this default value only if you have SAConnection::setAPI method with SAPI object initialized with SA_SQLServer_Client constant before

For more details see Getting Started - Connect to Database, SAConnection object, SAConnection::Connect.

Transaction isolation levels

SQL-92 defines four isolation levels, all of which are supported by SQLAPI++:

• Read uncommitted (the lowest level where transactions are isolated just enough to ensure that physically corrupt data is not read)
• Read committed
• Repeatable read
• Serializable (the highest level, where transactions are completely isolated from one another)

SQLAPI++ maps different isolation levels on SQL Server (OLEDB) in the following way:

In addition to the SQL-92 levels, if you specify 'snapshot' isolation level, it will be mapped as: SA_Snapshot → ISOLATIONLEVEL_SNAPSHOT.

For more details see SAConnection::setIsolationLevel.

Working with Long or Lob (CLob, BLob) data

When fetching data SQLAPI++ detects data types of the columns in the result set and maps those types to internal library types. The mapping determines which native APIs the library will use for fetching LOB data.

The table below shows how SQLAPI++ maps SQL Server server data types to Long/Lob library types:

When binding input data from your program the reverse mapping is taking place. The SQLAPI++ data type you use for input markers determines what native API program types will be used for sending Long/Lob data to the server.

For additional information see Getting Started - Handle Long/CLob/BLob.

Returning output parameters

SQL Server stored procedures can have integer return codes and output parameters. The return codes and output parameters are sent in the last packet from the server and are therefore not available to the application until all result sets from stored procedure (if any) are completely processed using SACommand::FetchNext method.

SQLAPI++ library automatically creates SAParam object to represent function return value. You can refer to this SAParam object using SQLAPI++ predefined name "RETURN_VALUE".

SQLAPI++ library may have difficulties with output [n]varchar(max) and varbinary(max) parameters because they are not supported by some specific OLEDB API versions.

For additional information see SACommand::Execute, SAParam object, Getting Started - Get Output Parameters.

Cancelling queries

Using SACommand::Cancel method you can cancel the following types of processing on a statement:

• function running asynchronously on the statement
• function running on the statement on another thread

SQLAPI++ calls ICommand::Cancel function to cancel a query. To get more details see ICommand::Cancel function description in native SQL Server (OLEDB) documentation.

For additional information see SACommand::Cancel.

Connection, command, parameter and field options

Specific options applicable to SQL Server (OLEDB):

DBPROP_SSCE_ENCRYPTDATABASE
DBPROP_SSCE_TEMPFILE_DIRECTORY
DBPROP_SSCE_TEMPFILE_MAX_SIZE
DBPROP_SSCE_DEFAULT_LOCK_ESCALATION
DBPROP_SSCE_AUTO_SHRINK_THRESHOLD
DBPROP_SSCE_MAX_DATABASE_SIZE
DBPROP_SSCE_FLUSH_INTERVAL
DBPROP_SSCE_DEFAULT_LOCK_TIMEOUT
DBPROP_SSCE_ENCRYPTIONMODE
DBPROP_SSCE_MAXBUFFERSIZE
DBPROP_SSCE_DBCASESENSITIVE

For additional information see SAOptions::setOption.

Using native SQL Server (OLEDB) API

You can call client specific API functions which are not directly supported by SQLAPI++ library. SAConnection::NativeAPI method returns a pointer to the set of native API functions available for SQL Server. To use the database API directly you have to downcast this IsaAPI pointer to the appropriate type and use its implementation-specific members. The following example shows what type cast you have to make and what additional header file you have to include to work with SQL Server (OLEDB) API. Note that using appropriate type casting depends on an API (that generally mean that you have to explicitly check client version before casting, see SAConnection::ClientVersion method).

To use native API you need to add SQL Server (OLEDB) specific #include and cast the result of SAConnection::NativeAPI to class ssOleDbAPI:

#include "ssOleDbAPI.h"

IsaAPI *pApi = con.NativeAPI();
ssOleDbAPI *pNativeAPI = (ssOleDbAPI *)pApi;

To get more information about SQL Server API functions see SQL Server (OLEDB) documentation.

For additional information see SAConnection::NativeAPI.

Getting native SQL Server (OLEDB) connection related handles

You have to use native API handles when you want to call specific SQL Server (OLEDB) API functions which are not directly supported by the library. API functions usually need to receive one or more active handles as parameters. SAConnection::NativeHandles method returns a pointer to the set of native API connection related handles. To use API handles directly you have to downcast saConnectionHandles pointer to the appropriate type and use its implementation-specific members.

To access native connection handles you need to add SQL Server (OLEDB) specific #include and cast the result to class ssOleDbConnectionHandles:

#include "ssOleDbAPI.h"

saConnectionHandles *pHandles = con.NativeHandles();
ssOleDbConnectionHandles *pNativeHandles = (ssOleDbConnectionHandles*)pHandles;

To get more information about SQL Server API functions and handles see SQL Server (OLEDB) specific documentation.

For additional information see SAConnection::NativeHandles.

Getting native SQL Server (OLEDB) command related handles

You have to use native API handles when you want to call specific SQL Server (OLEDB) API functions which are not directly supported by the library. API functions usually need to receive one or more active handles as parameters. SACommand::NativeHandles method returns a pointer to the set of native API command related handles. To use API handles directly you have to downcast saCommandHandles pointer to the appropriate type and use its implementation-specific members.

To access native command handles you need to add SQL Server (OLEDB) specific #include and cast the result to class ssOleDbCommandHandles:

#include "ssOleDbAPI.h"

saCommandHandles *pHandles = cmd.NativeHandles();
ssOleDbCommandHandles *pNativeHandles = (ssOleDbCommandHandles*)pHandles;

To get more information about SQL Server API functions and handles see SQL Server (OLEDB) specific documentation.

For additional information see SACommand::NativeHandles.

Error handling

When an error occurs when executing a SQL statement SQLAPI++ library throws an exception of type SAException and SAException::ErrPos method returns error position in the SQL statement.

In SQL Server (OLEDB) API SAException::ErrPos method returns the number of the line within SQL statement where the error occurred.

For additional information see Getting Started - Error Handling, SAException object.