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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 extensions
You 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 Guide
The 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 events
This section describes exceptions and events, and explains how to handle them in DataBlade® API modules.
Database server exceptions
When the database server or a UDR raises a database server exception, the DataBlade® API invokes any callbacks that are registered for the exception.
Understanding database server exceptions
A database server exception is an unexpected condition that occurs within the database server.
Status variables
To identify the particular cause of an exception, the database server sets the SQLSTATE and SQLCODE status variables. The SQLSTATE status variable holds a five-character code that is compliant with ANSI and X/Open standards. The SQLCODE status variable holds an integer value that is specific to HCL Informix®.
The SQLSTATE status value
The SQLSTATE status variable is a five-character string that the database server sets after it executes each DataBlade® API function. The value of SQLSTATE indicates the status of the function execution. The SQLSTATE status variable is compliant with ANSI and X/Open standards.
Identify runtime errors with SQLSTATE

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.
- Informix® extensions and DataBlade® modules
  These topics describe how to use built-in database extensions and separately installed DataBlade® modules.
- Creating extensions
  You 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 Guide
    The Informix® DataBlade® API Programmer's Guide describes information about the DataBlade API, the C-language application programming interface (API) provided with HCL Informix.
    - DataBlade® API overview
    - Data manipulation
    - Database access
      - Connection handling
        This section describes how to initialize, establish, and close connections.
      - Execute SQL statements
        One basic task of a DataBlade® API module is to send SQL statements to the database server for execution.
      - Execute user-defined routines
        This section provides information about how to call a user-defined routine (UDR).
      - Exceptions and events
        This section describes exceptions and events, and explains how to handle them in DataBlade® API modules.
        DataBlade® API event types
        For a DataBlade® API module, an event is a communication from HCL Informix® software that indicates the existence of some predefined condition, usually the occurrence of an exception (warning or error). The DataBlade API represents an event as one of the enumerated values of the MI_EVENT_TYPE data type.
        Event-handling mechanisms
        An event-handling mechanism provides a way for one DataBlade® API module to inform another module (or another part of the same module) that an event has occurred during execution of a function.
        Callback functions
        To 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.
        Database server exceptions
        When the database server or a UDR raises a database server exception, the DataBlade® API invokes any callbacks that are registered for the exception.
        Understanding database server exceptions
        A database server exception is an unexpected condition that occurs within the database server.
        Warnings and errors
        Status variables
        To identify the particular cause of an exception, the database server sets the SQLSTATE and SQLCODE status variables. The SQLSTATE status variable holds a five-character code that is compliant with ANSI and X/Open standards. The SQLCODE status variable holds an integer value that is specific to HCL Informix®.
        The SQLSTATE status value
        The SQLSTATE status variable is a five-character string that the database server sets after it executes each DataBlade® API function. The value of SQLSTATE indicates the status of the function execution. The SQLSTATE status variable is compliant with ANSI and X/Open standards.
        Identify warnings with SQLSTATE
        Identify runtime errors with SQLSTATE
        SQLCODE status value
        Each SQLSTATE value also has an associated status code that is specific to HCL Informix®. The database server saves this status code in the SQLCODE status variable. The SQLCODE variable is an integer that indicates whether the SQL statement succeeded or failed.
        Overriding the default exception handling
        By default, the DataBlade® API stops the current statement when the statement generates a database runtime error and continues execution when the statement generates a database warning.
        Return error information to the caller
        The fourth argument of a callback function is a pointer to callback user data. The user data is a C variable or structure that contains application-specific information that a callback can use.
        Handling multiple exceptions
        The database server can generate multiple exceptions for a single SQL statement.
        Raise an exception
        If a DataBlade® API module detects an error, it can use the mi_db_error_raise() function to raise an exception.
        State-transition events
        When the database server raises a state-transition event, the database server invokes any callbacks registered for the state transition. This section provides information about state-transition handling in DataBlade® API modules, including an explanation of state-transition events and a description of how to handle a state-transition event in a C UDR and a client LIBMI application.
        Client LIBMI errors
        The DataBlade® API throws the MI_Client_Library_Error event to indicate an error in the client LIBMI library.
      - XA-compliant external data sources
    - Create user-defined routines
    - Appendix
      This section contains additional reference information.
  - DataBlade® API Function Reference
    The Informix® DataBlade® API Function Reference describes the DataBlade API functions and the subset of Informix ESQL/C functions that the DataBlade API supports.
  - DataBlade® Developers Kit
    The DataBlade® Developers Kit (DBDK) guides contain information about the tools you can use to develop and package DataBlade modules, which extend the functionality of HCL Informix® databases.
  - J/Foundation Developer's Guide
    The J/Foundation Developer's Guide describes how to write user-defined routines (UDRs) in the Java™ programming language for Informix®.
  - R-Tree Index User's Guide
    The Informix® R-Tree Index User's Guide describes the HCL Informix R-tree secondary access method and how to access and use its components.
  - User-Defined Routines and Data Types Developer's Guide
    The Informix® User-Defined Routines and Data Types Developer's Guide describes how to define new data types and enable user-defined routines (UDRs) to extend HCL Informix.
  - Virtual-Table Interface Guide
    The 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.
  - Virtual-Index Interface Guide
    The Informix® Virtual-Index Interface Programmer's Guide explains how to create a secondary access method with the Virtual-Index Interface (VII) to extend the built-in indexing schemes of HCL Informix typically with a DataBlade® module.

Identify runtime errors with SQLSTATE

When an SQL statement results in a runtime error, the database server takes the following actions:

Sets the class code of SQLSTATE to a value greater than "02" (see Status conditions in SQLSTATE).
Sets the subclass code of SQLSTATE to a unique value that indicates the cause of the error.
Raises an MI_Exception event with an MI_EXCEPTION exception level.

The class and subclass codes of SQLSTATE identify the particular error. For errors that are specific to HCL Informix® (SQLSTATE is "IX000"), you can also check the value of the SQLCODE variable to identify the error.

Tip: The database server sets SQLSTATE to "02000" (class = "02") when a SELECT or FETCH statement encounters NOT FOUND (or END OF DATA). However, the NOT FOUND condition does not cause a database server exception. Therefore, you do not use SQLSTATE to detect this condition from within a callback of a DataBlade® API module. Instead, your DataBlade® API module can check for the MI_NO_MORE_RESULTS return code from the mi_get_result() function.