- pg_extension_name: pg_readme pg_extension_version: 0.7.0 pg_readme_generated_at: 2024-09-02 22:38:30.962606+01 pg_readme_version: 0.7.0
The pg_readme PostgreSQL extension

pg_extension_name: pg_readme pg_extension_version: 0.7.0 pg_readme_generated_at: 2024-09-02 22:38:30.962606+01 pg_readme_version: 0.7.0

The `pg_readme` PostgreSQL extension

The pg_readme PostgreSQL extension provides functions to generate a README.md document for a database extension or schema, based on COMMENT objects found in the pg_description system catalog.

Usage

To use pg_readme in your extension, the most self-documenting way to do it is to create a function that calls the readme.pg_extension_readme(name) function. Here is an example take from the pg_rowalesce extension:

create function pg_rowalesce_readme()
    returns text
    volatile
    set search_path from current
    set pg_readme.include_view_definitions to 'true'
    set pg_readme.include_routine_definition_like to '{test__%}'
    language plpgsql
    as $plpgsql$
declare
    _readme text;
begin
    create extension if not exists pg_readme
        with version '0.1.0';
    _readme := pg_extension_readme('pg_rowalesce'::name);
    raise transaction_rollback;  -- to drop extension if we happened to `CREATE EXTENSION` for just this.
exception
    when transaction_rollback then
        return _readme;
end;
$plpgsql$;

In the above example, the pg_readme.* settings are (quite redundantly) set to their default values. There is no need to add pg_readme to the list of requirements in your extension’s control file; after all, the extension is only intermittently required, by you, when you need to update your extension’s README.md.

To make it easy (and self-documenting) to update the readme, add something like the following recipe to the bottom of your extension’s Makefile:

README.md: README.sql install
        psql --quiet postgres < $< > $@

And turn the README.sql into something like this (again an example from pg_rowalesce):

\pset tuples_only
\pset format unaligned

begin;

create schema rowalesce;

create extension pg_rowalesce
    with schema rowalesce
    cascade;

select rowalesce.pg_rowalesce_readme();

rollback;

Now you can update your README.md by running:

make README.md

COMMENT (also on your extension), play with it, and never go back. And don’t forget to send me the pull requests for you enhancements.

Markdown

The pg_readme author has made the choice for Markdown, not out of love for Markdown, but out of practicality: Markdown, in all its neo-formal interprations, has become ubiquitous. Also, it has a straight-forward fall-through to (X)HTML. And we’re not creating tech. books here (where TEI or DocBook would have been the superior choice); we’re merely generating online/digital documentation on the basis of inline COMMENTs.

To make the pain of Markdown’s many competing extensions and implementations somewhat bearable, pg_readme attempts to stick to those Markdown constructs that are valid both according to:

GitHub Flavored Markdown (GFM), and
CommonMark.

“Attempts to”, because pg_readme relies heavily on MarkDown tables, which are supported by GFM, but not by CommonMark.

Processing instructions

pg_readme has support for a bunch of special XML processing instructions that you can include in the Markdown COMMENT ON EXTENSION or COMMENT ON SCHEMA objects:

<?pg-readme-reference?> will be replaced with a full reference with all the objects found by pg_readme that belong to the schema or extension (when pg_schema_readme() or pg_extension_readme() are run respectively.
<?pg-readme-colophon?> adds a colophon with information about pg_readme to the text.

The following pseudo-attributes are supported for these processing instructions:

(These attributes are called pseudo-attributes, because the XML spec does not prescribe any particular structure for a processing instruction’s content.

Extension-specific settings

| Setting | Default | | –––––––––––––––––––––– | ————————————————————— | | pg_readme.include_view_definitions | true | | pg_readme.readme_url | 'https://github.com/bigsmoke/pg_readme/blob/master/README.md' | | pg_readme.include_routine_definitions_like | '{test__%}' | | pg_readme.include_this_routine_definition | null |

pg_readme.include_this_routine_definition is meant to be only used on a routine-local level to make sure that the definition for that particular routine is either always or never included in the reference, regardless of the pg_readme.include_routine_definitions_like setting.

For pg_readme version 0.3.0, pg_readme.include_routine_definitions has been deprecated in favor of pg_readme.include_routine_definitions_like, and pg_readme.include_routine_definitions is now interpreted as:

To-dos and to-maybes

Missing features

Table synopsis is not generated yet.

Ideas for improvement

Support for <?pg-readme-install?> PI could be nice.
Support for a <?pg-readme-table-rows?> PI in the COMMENT of specific tables could be a nice addition for extensions/schemas that have type-type tables.
Automatically turning references to objects from other/builtin extensions or schemas into links could be a plus. But this might also render the raw markup unreadable. That, at least, would be a good argument against doing the same for extension-local object references.

The origins of the `pg_readme` extension

pg_readme, together with a sizeable number of other PostgreSQL extensions, was developed as part of the backend for the super-scalable FlashMQ MQTT SaaS service. Bundling and releasing this code publically has:

made the PostgreSQL schema architecture cleaner, with fewer interdependencies;
made the documentation more complete and up-to-date;
increased the amount of polish; and
reduced the number of rough edges.

The public gaze does improve quality!

Object reference

Routines

Function: `pg_extension_readme (name)`

pg_extension_readme() automatically generates a README.md for the given extension, taking the COMMENT ON EXTENSION as the prelude, and optionally adding a full reference (with neatly layed out object characteristics from the pg_catalog) in the place where a <?pg-readme-reference?> processing instruction is encountered in the COMMENT ON EXTENSION.

See the Processing instructions section for details about the processing instructions that are recognized and which pseudo-attributes they support.

Function arguments:

| Arg. # | Arg. mode | Argument name | Argument type | Default expression | | —— | ––––– | —————————————————————– | –––––––––––––––––––––––––––––––––– | —————–– | | $1 | IN | | name | |

Function return type: text

Function attributes: STABLE

Function-local settings:

SET search_path TO readme, ext, pg_temp

Function: `pg_readme_colophon (pg_readme_collection_type, name, smallint, boolean, text)`

pg_readme_colophon() is a function internal to pg_readme that is used by pg_readme_pis_process() to replace <?pg-readme-colophon?> processing instructions with a standard colophon indicating that pg_readme was used to generate a schema or extension README.

See the Processing instructions section for an overview of the processing instructions and their pseudo-attributes.

Function arguments:

| Arg. # | Arg. mode | Argument name | Argument type | Default expression | | —— | ––––– | —————————————————————– | –––––––––––––––––––––––––––––––––– | —————–– | | $1 | IN | collection_type$ | pg_readme_collection_type | | | $2 | IN | collection_name$ | name | | | $3 | IN | context_division_depth$ | smallint | 1 | | $4 | IN | context_division_is_self$ | boolean | false | | $5 | IN | division_title$ | text | 'Colophon'::text |

Function return type: text

Function attributes: IMMUTABLE, LEAKPROOF, PARALLEL SAFE

Function: `pg_readme_meta_pgxn()`

Returns the JSON meta data that has to go into the META.json file needed for PGXN—PostgreSQL Extension Network packages.

The Makefile includes a recipe to allow the developer to: make META.json to refresh the meta file with the function’s current output, including the default_version.

Function return type: jsonb

Function attributes: STABLE

Function: `pg_readme_object_reference (pg_readme_objects_for_reference, pg_readme_collection_type, name, smallint, boolean, text)`

pg_readme_object_reference() is a function internal to pg_readme that is delegated to by pg_readme_pis_process() to replace <?pg-readme-reference?> processing instructions with a standard colophon indicating that pg_readme was used to generate a schema or extension README.

See the Processing instructions section for an overview of the processing instructions and their pseudo-attributes.

Function arguments:

| Arg. # | Arg. mode | Argument name | Argument type | Default expression | | —— | ––––– | —————————————————————– | –––––––––––––––––––––––––––––––––– | —————–– | | $1 | IN | objects$ | pg_readme_objects_for_reference | | | $2 | IN | collection_type$ | pg_readme_collection_type | | | $3 | IN | collection_name$ | name | | | $4 | IN | context_division_depth$ | smallint | 1 | | $5 | IN | context_division_is_self$ | boolean | false | | $6 | IN | division_title$ | text | 'Object reference'::text |

Function return type: text

Function attributes: STABLE

Function-local settings:

SET search_path TO readme, ext, pg_temp

Function: `pg_readme_object_reference__rel_attr_list (pg_class)`

Function arguments:

| Arg. # | Arg. mode | Argument name | Argument type | Default expression | | —— | ––––– | —————————————————————– | –––––––––––––––––––––––––––––––––– | —————–– | | $1 | IN | | pg_class | |

Function return type: text

Function attributes: STABLE

Function: `pg_readme_pi_pseudo_attrs (text, text)`

pg_readme_pi_pseudo_attrs() extracts the pseudo-attributes from the XML processing instruction with the given pi_target$ found in the givenhaystack$ argument.

See the test__pg_readme_pi_pseudo_attrs() procedure source for examples.

Function arguments:

| Arg. # | Arg. mode | Argument name | Argument type | Default expression | | —— | ––––– | —————————————————————– | –––––––––––––––––––––––––––––––––– | —————–– | | $1 | IN | haystack$ | text | | | $2 | IN | pi_target$ | text | |

Function return type: hstore

Function attributes: IMMUTABLE, LEAKPROOF, RETURNS NULL ON NULL INPUT, PARALLEL SAFE

Function: `pg_readme_pis_process (text, pg_readme_collection_type, name, pg_readme_objects_for_reference)`

pg_readme_object_reference() is a function internal to pg_readme that is responsible for replacing processing instructions in the source text with generated content.

See the Processing instructions section for an overview of the processing instructions and their pseudo-attributes.

Function arguments:

| Arg. # | Arg. mode | Argument name | Argument type | Default expression | | —— | ––––– | —————————————————————– | –––––––––––––––––––––––––––––––––– | —————–– | | $1 | IN | unprocessed$ | text | | | $2 | IN | collection_type$ | pg_readme_collection_type | | | $3 | IN | collection_name$ | name | | | $4 | IN | objects$ | pg_readme_objects_for_reference | |

Function return type: text

Function attributes: STABLE, LEAKPROOF, RETURNS NULL ON NULL INPUT, PARALLEL SAFE

Function-local settings:

SET search_path TO readme, ext, pg_temp

Function: `pg_schema_readme (regnamespace)`

pg_schema_readme() automatically generates a README.md for the given schema, taking the COMMENT ON SCHEMA as the prelude, and optionally adding a full reference (with neatly layed out object characteristics from the pg_catalog) in the place where a <?pg-readme-reference?> processing instruction is encountered in the COMMENT ON SCHEMA.

See the Processing instructions section for details about the processing instructions that are recognized and which pseudo-attributes they support.

Function arguments:

| Arg. # | Arg. mode | Argument name | Argument type | Default expression | | —— | ––––– | —————————————————————– | –––––––––––––––––––––––––––––––––– | —————–– | | $1 | IN | | regnamespace | |

Function return type: text

Function attributes: STABLE

Function-local settings:

SET search_path TO readme, ext, pg_temp

Function: `string_diff (text, text)`

Function arguments:

| Arg. # | Arg. mode | Argument name | Argument type | Default expression | | —— | ––––– | —————————————————————– | –––––––––––––––––––––––––––––––––– | —————–– | | $1 | IN | | text | | | $2 | IN | | text | |

Function return type: text

Function attributes: IMMUTABLE, LEAKPROOF, RETURNS NULL ON NULL INPUT

Procedure: `test__pg_readme()`

This routine tests the pg_readme extension.

The routine name is compliant with the pg_tst extension. An intentional choice has been made to not depend on the pg_tst extension its test runner or developer-friendly assertions to keep the number of inter-extension dependencies to a minimum.

Procedure-local settings:

SET search_path TO readme, ext, pg_temp
SET pg_readme.include_this_routine_definition TO false
SET plpgsql.check_asserts TO true

Procedure: `test__pg_readme_pi_pseudo_attrs()`

This routine tests the pg_readme_pi_pseudo_attrs() function.

Procedure-local settings:

SET search_path TO readme, ext, pg_temp

CREATE OR REPLACE PROCEDURE readme.test__pg_readme_pi_pseudo_attrs()
 LANGUAGE plpgsql
 SET search_path TO 'readme', 'ext', 'pg_temp'
AS $procedure$
begin
    assert pg_readme_pi_pseudo_attrs(
        '<?muizen-stapje soort="woelmuis" hem-of-haar="piep" a1="4"?>',
        'muizen-stapje'
    ) = hstore('soort=>woelmuis, hem-of-haar=>piep, a1=>4');

    assert pg_readme_pi_pseudo_attrs(
        'Blabla bla <?muizen-stapje soort="woelmuis" hem-of-haar="piep"?> Frotsepots',
        'muizen-stapje'
    ) = hstore('soort=>woelmuis, hem-of-haar=>piep');

    assert pg_readme_pi_pseudo_attrs(
        'Blabla bla <?muizen-stapje ?> Frotsepots',
        'muizen-stapje'
    ) is null;
end;
$procedure$

Types

The following extra types have been defined besides the implicit composite types of the tables and views in this extension.

Composite type: `pg_readme_objects_for_reference`

CREATE TYPE pg_readme_objects_for_reference AS (
  table_objects regclass[],
  view_objects regclass[],
  procedure_objects regprocedure[],
  operator_objects regoperator[],
  type_objects regtype[]
);

Domain: `pg_readme_collection_type`

CREATE DOMAIN pg_readme_collection_type AS text
  CHECK ((VALUE = ANY (ARRAY['extension'::text, 'schema'::text])));

Authors and contributors

Rowan originated this extension in 2022 while developing the PostgreSQL backend for the FlashMQ SaaS MQTT cloud broker. Rowan does not like to see himself as a tech person or a tech writer, but, much to his chagrin, he is. Some of his chagrin about his disdain for the IT industry he poured into a book: Why Programming Still Sucks. Much more than a “tech bro”, he identifies as a garden gnome, fairy and ork rolled into one, and his passion is really to regreen and reenchant his environment. One of his proudest achievements is to be the third generation ecological gardener to grow the wild garden around his beautiful family holiday home in the forest of Norg, Drenthe, the Netherlands (available for rent!).

Colophon

This README.md for the pg_readme extension was automatically generated using the pg_readme PostgreSQL extension.

PGXN

PostgreSQL Extension Network

Contents

pg_extension_name: pg_readme pg_extension_version: 0.7.0 pg_readme_generated_at: 2024-09-02 22:38:30.962606+01 pg_readme_version: 0.7.0

The pg_readme PostgreSQL extension

Usage

Markdown

Processing instructions

Extension-specific settings

To-dos and to-maybes

Missing features

Ideas for improvement

The origins of the pg_readme extension

Object reference

Routines

Function: pg_extension_readme (name)

Function: pg_readme_colophon (pg_readme_collection_type, name, smallint, boolean, text)

Function: pg_readme_meta_pgxn()

Function: pg_readme_object_reference (pg_readme_objects_for_reference, pg_readme_collection_type, name, smallint, boolean, text)

Function: pg_readme_object_reference__rel_attr_list (pg_class)

Function: pg_readme_pi_pseudo_attrs (text, text)

Function: pg_readme_pis_process (text, pg_readme_collection_type, name, pg_readme_objects_for_reference)

Function: pg_schema_readme (regnamespace)

Function: string_diff (text, text)

Procedure: test__pg_readme()

Procedure: test__pg_readme_pi_pseudo_attrs()

Types

Composite type: pg_readme_objects_for_reference

Domain: pg_readme_collection_type

Authors and contributors

Colophon

The `pg_readme` PostgreSQL extension

The origins of the `pg_readme` extension

Function: `pg_extension_readme (name)`

Function: `pg_readme_colophon (pg_readme_collection_type, name, smallint, boolean, text)`

Function: `pg_readme_meta_pgxn()`

Function: `pg_readme_object_reference (pg_readme_objects_for_reference, pg_readme_collection_type, name, smallint, boolean, text)`

Function: `pg_readme_object_reference__rel_attr_list (pg_class)`

Function: `pg_readme_pi_pseudo_attrs (text, text)`

Function: `pg_readme_pis_process (text, pg_readme_collection_type, name, pg_readme_objects_for_reference)`

Function: `pg_schema_readme (regnamespace)`

Function: `string_diff (text, text)`

Procedure: `test__pg_readme()`

Procedure: `test__pg_readme_pi_pseudo_attrs()`

Composite type: `pg_readme_objects_for_reference`

Domain: `pg_readme_collection_type`