GSP
Quick Navigator

Search Site

Unix VPS
A - Starter
B - Basic
C - Preferred
D - Commercial
MPS - Dedicated
Previous VPSs
* Sign Up! *

Support
Contact Us
Online Help
Handbooks
Domain Status
Man Pages

FAQ
Virtual Servers
Pricing
Billing
Technical

Network
Facilities
Connectivity
Topology Map

Miscellaneous
Server Agreement
Year 2038
Credits
 

USA Flag

 

 

Man Pages


Manual Reference Pages  -  CREATE_TRANSFORM (7)

.ds Aq ’

NAME

CREATE_TRANSFORM - define a new transform

CONTENTS

SYNOPSIS

CREATE [ OR REPLACE ] TRANSFORM FOR type_name LANGUAGE lang_name (
    FROM SQL WITH FUNCTION from_sql_function_name (argument_type [, ...]),
    TO SQL WITH FUNCTION to_sql_function_name (argument_type [, ...])
);

DESCRIPTION

CREATE TRANSFORM defines a new transform. CREATE OR REPLACE TRANSFORM will either create a new transform, or replace an existing definition.

A transform specifies how to adapt a data type to a procedural language. For example, when writing a function in PL/Python using the hstore type, PL/Python has no prior knowledge how to present hstore values in the Python environment. Language implementations usually default to using the text representation, but that is inconvenient when, for example, an associative array or a list would be more appropriate.

A transform specifies two functions:

o

o A \(lqfrom SQL\(rq function that converts the type from the SQL environment to the language. This function will be invoked on the arguments of a function written in the language.

o

o A \(lqto SQL\(rq function that converts the type from the language to the SQL environment. This function will be invoked on the return value of a function written in the language.

It is not necessary to provide both of these functions. If one is not specified, the language-specific default behavior will be used if necessary. (To prevent a transformation in a certain direction from happening at all, you could also write a transform function that always errors out.)

To be able to create a transform, you must own and have USAGE privilege on the type, have USAGE privilege on the language, and own and have EXECUTE privilege on the from-SQL and to-SQL functions, if specified.

PARAMETERS

type_name

The name of the data type of the transform.

lang_name

The name of the language of the transform.

from_sql_function_name(argument_type [, ...])

The name of the function for converting the type from the SQL environment to the language. It must take one argument of type internal and return type internal. The actual argument will be of the type for the transform, and the function should be coded as if it were. (But it is not allowed to declare an SQL-level function returning internal without at least one argument of type internal.) The actual return value will be something specific to the language implementation.

to_sql_function_name(argument_type [, ...])

The name of the function for converting the type from the language to the SQL environment. It must take one argument of type internal and return the type that is the type for the transform. The actual argument value will be something specific to the language implementation.

NOTES

Use DROP TRANSFORM (DROP_TRANSFORM(7)) to remove transforms.

EXAMPLES

To create a transform for type hstore and language plpythonu, first set up the type and the language:

CREATE TYPE hstore ...;

CREATE LANGUAGE plpythonu ...;

Then create the necessary functions:

CREATE FUNCTION hstore_to_plpython(val internal) RETURNS internal
LANGUAGE C STRICT IMMUTABLE
AS ...;

CREATE FUNCTION plpython_to_hstore(val internal) RETURNS hstore LANGUAGE C STRICT IMMUTABLE AS ...;

And finally create the transform to connect them all together:

CREATE TRANSFORM FOR hstore LANGUAGE plpythonu (
    FROM SQL WITH FUNCTION hstore_to_plpython(internal),
    TO SQL WITH FUNCTION plpython_to_hstore(internal)
);

In practice, these commands would be wrapped up in extensions.

The contrib section contains a number of extensions that provide transforms, which can serve as real-world examples.

COMPATIBILITY

This form of CREATE TRANSFORM is a PostgreSQL extension. There is a CREATE TRANSFORM command in the SQL standard, but it is for adapting data types to client languages. That usage is not supported by PostgreSQL.

SEE ALSO

CREATE FUNCTION (CREATE_FUNCTION(7)), CREATE LANGUAGE (CREATE_LANGUAGE(7)), CREATE TYPE (CREATE_TYPE(7)), DROP TRANSFORM (DROP_TRANSFORM(7))

Search for    or go to Top of page |  Section 7 |  Main Index


PostgreSQL 9.5.2 CREATE TRANSFORM (7) 2016

Powered by GSP Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.