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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
Extend data typesThis section describes the ways to extend data types with C user-defined routines (UDRs).
Create an Opaque Data TypeThis section describes how to design and write an opaque data type.
Write opaque-type support functionsThe database server does not know the internal representation of an opaque type. To handle the internal representation, you write opaque-type support functions. These support functions tell the database server how to interact with the opaque type.
Stream support functions

Stream support functions

The following support functions convert a UDT to or from a stream representation while reading the UDT from a stream or writing the UDT to a stream.

streamwrite(): Conversion of opaque-type data from its binary representation to its stream representation
streamread(): Conversion of opaque-type data from its stream representation to its binary representation

The stream representation is self-contained and includes enough information to enable the streamread() function to recreate the UDT instance.

Important: If the UDT includes out-of-row data, the stream representation normally includes that data.

Enterprise Replication invokes the streamwrite() and streamread() support functions when replicating UDT columns. The streams it passes to these functions are Enterprise Replication streams, a write-only stream for streamwrite() and a read-only stream for streamread(). You cannot open or close an Enterprise Replication stream or use the mi_stream_setpos() or mi_stream_seek() function on it. For more information about Enterprise Replication, see the .

Important: If a column that includes out-of-row data is to be replicated, avoid placing a NOT NULL constraint on the column. Enterprise Replication collects out-of-row data for transmission after the user transaction has committed. Due to activity on the replicated row, the data might not exist at the time Enterprise Replication collects it for replication. In such cases, Enterprise Replication normally applies a NULL on the target system.

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