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Extending Informix®Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix® includes many built-in extensions that are fully integrated in the database server. Informix® also provides DataBlade® modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix®.
Creating extensionsYou can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
Virtual-Table Interface GuideThe Informix® Virtual-Table Interface Programmer's Guide explains how to create a primary access method with the Virtual-Table Interface (VTI) so that users have a single SQL interface to HCL Informix® tables and to data that does not conform to the storage scheme of HCL Informix®.
Purpose-function referenceThese topics describe the purpose functions that the access-method developer provides.
Purpose-function syntaxThe database server expects a particular prototype for each purpose function. As the access-method developer, you program the actions of a purpose function but must use the parameters and return values that the Virtual-Table Interface (VTI) prototypes specify.
The am_getbyid purpose functionThe database server calls am_getbyid instead of am_getnext to pass the row identifier instead of a scan descriptor. For example, the database server might obtain the row identifier from an index on the virtual table.

The am_getbyid purpose function

The database server calls am_getbyid instead of am_getnext to pass the row identifier instead of a scan descriptor. For example, the database server might obtain the row identifier from an index on the virtual table.

Syntax

mi_integer am_getbyid(MI_AM_TABLE_DESC *tableDesc,
   MI_ROW **retrow, mi_integer rowID)

tableDesc: Points to the table descriptor.
retrow: Points to the location where the function is to place a row structure that contains the fetched data.
rowID: Is the row identifier or physical address of the row to fetch.

Usage

The am_getbyid purpose function does not scan a table to find a qualifying row.

Possible row identifiers that rowID might point to include:

The sequence of this row within the fragment
An offset to an LO handle
A value that an external data manager assigns
A value that the access method assigns

As with am_getnext, am_getbyid first fetches the specified row and then passes the retrow pointer to mi_row_create() to build the composite MI_ROW value from fetched data.

Important: The database server does not call am_getbyid unless you set the am_rowids purpose flag.

For more information, see the purpose flag am_rowids in Settings purpose functions, flags, and values.

Return values

MI_OK: Indicates success.
MI_ERROR: Indicates failure.

Related topics

See the description of:

DataBlade® API function mi_row_create() in the Informix® DataBlade API Programmer's Guide

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