The Command object is created by an OLE DB consumer, or by a service provider on behalf of a consumer. A Command object is used to execute a DDM-specific command on a remote DDM server. The Command object currently supports executing Command Language commands on AS/400 DDM servers.
It is important not to confuse a command, which is an OLE COM object, and its command text, which is a string. Commands are generally used for data definition, such as creating a table or granting privileges, and data manipulation, such as updating or deleting rows. A special case of data manipulation using the Command object is opening a rowset (a table).
Before a consumer can use a command, it must determine if commands are supported. To do this, the consumer calls QueryInterface for IDBCreateCommand on a session. If this interface is exposed, the provider supports commands. To create a command, the consumer then calls IDBCreateCommand::CreateCommand on the session. A single session can be used to create multiple commands.
When the command is first created, it does not contain a command text. The consumer sets the command text with ICommandText::SetCommandText. Because the text command syntax is provider-specific, the consumer passes the GUID of the syntax to use. For use with the Microsoft® OLE DB Provider for AS/400 and VSAM, the GUID is DBGUID_DBSQL. Please note that under the OLE DB Provider for AS/400 and VSAM this GUID does not signify that the text command is a superset of ANSI SQL. The level at which the provider supports ANSI SQL is specified by the DBPROP_SQLSUPPORT property.
The syntax supported by the OLE DB Provider for AS/400 and VSAM for command text is as follows:
EXEC COMMAND DDMCmd
where DDMCmd is a DDM command-line string. Legal DDM command-line strings are documented in Chapter 5 of the AS/400 Distributed Data Manager User's Guide published by IBM.
The syntax supported by the OLE DB Provider for AS/400 and VSAM to open a rowset (table) using command text is as follows:
EXEC OPEN FileName
where FileName represents one of the following host file naming conventions:
| Host file type | File naming convention |
|---|---|
| VSAM Data Sets | DATASETNAME.FILENAME |
| Partitioned Data Sets | DATASETNAME.FILENAME(MEMBER) |
| OS/400 Files | LIBRARY/FILE |
| OS/400 Files | LIBRARY/FILENAME |
| OS/400 File Members | LIBRARY/FILE(MEMBER) |
| OS/400 File Members | LIBRARY.FILENAME(MEMBER) |
Note that if a member of a library contains a dot in the member name, the member name must be surrounded by double quotes. For example, if the member name is NAMES.DAT the proper syntax used to open a rowset using command text is as follows:
EXEC OPEN LIBRARY/FILE("NAMES.DAT")
To execute the command, the consumer calls ICommand::Execute. If the command text specifies the command to open a rowset, (an EXEC OPEN command), Execute instantiates the rowset and returns an interface pointer to it.
The following interfaces of the Command object are supported by the current version of the OLE DB Provider for AS/400 and VSAM: