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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
Connection handling
This section describes how to initialize, establish, and close connections.
Associate user data with a connection
The connection descriptor provides information about various data type structures associated with the current connection. In addition, you can store the address of private information, called user data, in the connection descriptor. The connection descriptor can hold this user-data pointer, which points to the private user-data information.

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.
        Session management
        Session management is the handling of a connection to a database server and the associated session within a DataBlade® API module. A session is the period of time that elapses between when a client application establishes a connection and when this connection is closed.
        Initializing a client connection
        Before a client LIBMI application can establish a connection, it must initialize the connection with the name of the database server and database to which it needs to connect.
        Establish a connection
        The DataBlade® API functions, mi_open() and mi_server_connect() (client only), are constructor functions for a connection descriptor.
        Associate user data with a connection
        The connection descriptor provides information about various data type structures associated with the current connection. In addition, you can store the address of private information, called user data, in the connection descriptor. The connection descriptor can hold this user-data pointer, which points to the private user-data information.
        Initialize the DataBlade® API
        Before you can use the DataBlade® API to communicate with the database server, you must make sure that it is initialized.
        Close a connection
        To close a connection, free the associated connection descriptor.
      - 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.
      - 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.

Associate user data with a connection

The connection descriptor provides information about various data type structures associated with the current connection. In addition, you can store the address of private information, called user data, in the connection descriptor. The connection descriptor can hold this user-data pointer, which points to the private user-data information.

For a list of the information the connection descriptor provides, see Session-context information in a connection descriptor.

Server only:

You allocate the user data with a DataBlade® API memory-management function from the shared memory of the database server. The memory duration of this user data must correspond with the connection descriptor that holds the user-data pointer, as the following table shows.


Type of connection descriptor	Memory duration of user data	Which UDRs can access user data
Public connection descriptor (with mi_open())	MI_COMMAND	All UDR invocations in the same SQL command have access to the connection descriptor that mi_open() returns.
Session-duration connection descriptor (with mi_get_session_connection())	MI_SESSION	All C UDR invocations in the session have access to the connection descriptor that mi_get_session_connection() returns.

Therefore, your user data is available to all UDRs that can access its connection descriptor.

Important: A session-duration connection descriptor is a restricted feature that can adversely affect your UDR if used incorrectly. Use it only when a public connection descriptor cannot support the task you need to perform.

Client only: The user data is allocated in client-side memory. Therefore, your user data is available to all DataBlade® API functions that execute in the session.

The following table shows the functions that the DataBlade® API provides to access the user data of a connection descriptor.

Table 1. DataBlade® API accessor functions for user data in the connection descriptor
DataBlade® API accessor function	User-state information
mi_get_connection_user_data()	Obtains the user-data pointer from the connection descriptor
mi_set_connection_user_data()	Sets the user-data pointer in the connection descriptor

The size of the connection user data is the size of a pointer of type void *. The DataBlade® API does not interpret or touch the associated user-data address, other than to store and retrieve it from the connection descriptor.