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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®.
Create user-defined routines
Develop a user-defined routineA C user-defined routine (UDR) is a UDR that is written in the C language and uses the server-side implementation of the DataBlade® API to communicate with the database server. C UDRs (functions and procedures) are implemented as C-language functions. DataBlade® modules often include C UDRs that are made available for use by registering them in the database.
Designing a UDRThis section provides the following design considerations for the development of a C UDR: development tools, uses of a UDR, portability, and insert and update operations.
Insert and update operations

Insert and update operations

An SPL routine has the restriction that it cannot perform INSERT or UPDATE operations in an SPL routine that is invoked from a DML statement. This restriction ensures that the SPL routine cannot change the state of the statement that invoked it.

This restriction is relaxed for UDRs. The database server issues an error if the table that is being accessed in the UDR is referenced in the statement that invoked it. If this is a nested UDR invocation, then the database server checks the chain of parent queries.

If a UDR is called as part of an INSERT, UPDATE, DELETE, or SELECT statement and if the referenced table appears in the chain of statements that eventually invoked the UDR, the called routine cannot execute any of the following statements:

ALTER FRAGMENT
ALTER INDEX
ALTER TABLE
DROP INDEX
DROP SYNONYM
DROP TABLE
DROP TRIGGER
DROP VIEW
RENAME COLUMN
RENAME TABLE

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