Is it possible to create a re-usable function with the PostgreSQL plv8 extension?

问题

I wanted to drop in google's open location code javascript implementation into PostgreSQL (using the plv8 extension) and make it available to encode/decode from PostGIS geometry/geography data types.

While I was successful, I wasn't able to work out how to only create a single function for the https://github.com/google/open-location-code/blob/master/js/src/openlocationcode.js file and I ended up putting a copy of that function into each function where I needed to encode/decode plus codes. When I attempted to pull it out into its own function, I could either get a string containing javascript or a string of [Object],[object] rather than a callable function.

Is this possible with the plv8 extension in PostgreSQL?

Incomplete code snippet example (full version here):

DROP FUNCTION IF EXISTS olc.encode(float,float,integer);

CREATE OR REPLACE FUNCTION olc.encode(
    p_latitude double precision,
    p_longitude double precision,
    p_code_length integer DEFAULT 10
)
  RETURNS text AS
$BODY$


 var f  =  function () {
    var OpenLocationCode = {};

    /**
     * Provides a normal precision code, approximately 14x14 meters.
     * @const {number}
     */
    OpenLocationCode.CODE_PRECISION_NORMAL = 10;

    /**
     * Provides an extra precision code, approximately 2x3 meters.
     * @const {number}
     */
    OpenLocationCode.CODE_PRECISION_EXTRA = 11;

    // A separator used to break the code into two parts to aid memorability.
    var SEPARATOR_ = '+';

    // The number of characters to place before the separator.
    var SEPARATOR_POSITION_ = 8;

    // The character used to pad codes.
    var PADDING_CHARACTER_ = '0';

回答1:

You have two options.

Store the source code of the function in a special database table and load it using select and eval(). Read about details in this answer: Can plv8 JavaScript language extension call 3rd party libraries?
Place the function in an initialization module and set this module using configuration parameter plv8.start_proc so it is executed automatically on start-up. You can find details in the PL/v8 documentation.

The second option is really handy and does not need an additional table, but may seem a bit tricky. A simple example: we want to have a function square_of_sum(a, b) predefined in all our plv8 functions. First, create the initialization function:

create or replace function plv8_init()
returns void language plv8 as $$

    square_of_sum = function(a, b) {
        return (a+ b)* (a+ b)
    }

$$;

set the initialization function for the database:

alter database my_database set plv8.start_proc to plv8_init;

and close the current connection.

In all subsequent sessions the function square_of_sum(a, b) is known in every other plv8 function, e.g.:

create or replace function js_test()
returns int language plv8 as $$
    return square_of_sum(3, 2)
$$;

select js_test();

 js_test
---------
      25
(1 row)

来源：https://stackoverflow.com/questions/49631866/is-it-possible-to-create-a-re-usable-function-with-the-postgresql-plv8-extension

标签

postgresql

plv8