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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
Connection handlingThis section describes how to initialize, establish, and close connections.
Session managementSession 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.
UDR connection (Server)A C UDR cannot establish a connection to the database server. It must run within an existing session, which a client application begins when it establishes a client connection.

UDR connection (Server)

A C UDR cannot establish a connection to the database server. It must run within an existing session, which a client application begins when it establishes a client connection.

To obtain access to an existing session, a UDR establishes a UDR connection. A UDR uses the mi_open() function (with NULL-valued pointers for all arguments) to establish a UDR connection. A UDR can have one or more UDR connections to the session.

Because a C UDR cannot establish a connection, it never begins a session. Instead, it inherits the context of an existing session from the SQL statement that invokes the UDR. This SQL statement executes within a session that the client application has begun. Therefore, the UDR is already connected to a particular database server and has access to a database that has already been opened. The UDR is also inside the current transaction.

A UDR connection provides access to the session context. This session context persists across all invocations of a UDR instance because a UDR connection has the duration of an SQL command. That is, the mi_open() function and its corresponding mi_close() function do not necessarily have to be called from within the same invocation of the UDR but they do have to be called within the same instance.

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