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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.
DataBlade® API Programmer's GuideThe Informix® DataBlade® API Programmer's Guide describes information about the DataBlade® API, the C-language application programming interface (API) provided with HCL Informix®.
Database access
Exceptions and eventsThis section describes exceptions and events, and explains how to handle them in DataBlade® API modules.
Callback functionsTo catch or handle an event, you create a C function called a callback function. In your DataBlade® API module, you can register callback functions to handle recovery from events. The DataBlade® API invokes a registered (and enabled) callback when the event associated with the callback occurs.
Write a callback functionWithin the body of a callback function, you provide the code that handles a particular event or events. Only certain tasks are valid within a callback. When a callback function is invoked for an event, the DataBlade® API passes information about the event to the callback.
Event informationWhen a callback function is invoked for a particular event, the DataBlade® API passes an event-type structure as the third parameter of this function. This event-type structure contains information about the event that triggered the callback.

Event information

When a callback function is invoked for a particular event, the DataBlade® API passes an event-type structure as the third parameter of this function. This event-type structure contains information about the event that triggered the callback.

The DataBlade API stores event information in one of the following structures based on the event type:

Exceptions and errors are stored in error descriptors.
State transitions are stored in transition descriptors.

The following table shows the event types and the corresponding event-type structures that describe them.


Event-type structure	Event type
Error descriptor (MI_ERROR_DESC)	MI_Exception MI_Client_Library_Error
Transition descriptor (MI_TRANSITION_DESC)	MI_EVENT_SAVEPOINT MI_EVENT_COMMIT_ABORT MI_EVENT_POST_XACT MI_EVENT_END_STMT MI_EVENT_END_XACT MI_EVENT_END_SESSION MI_Xact_State_Change

The milib.h header file defines the MI_ERROR_DESC and MI_TRANSITION_DESC structures.

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