Contents

• DDL eXtractor functions for PostgreSQL
  • Installation
  • Using

DDL eXtractor functions for PostgreSQL

This is an SQL-only extension for PostgreSQL that provides uniform functions for generating SQL Data Definition Language (DDL) scripts for objects created in a database. It contains a bunch of SQL functions to convert PostgreSQL system catalogs to nicely formatted snippets of SQL DDL, such as CREATE TABLE.

Some other SQL databases support commands like SHOW CREATE TABLE or provide other facilities for the purpose.

PostgreSQL currently doesn't provide overall in-server DDL extracting functions, but rather a separate pg_dump program. It is an external tool to the server and therefore requires shell access or local installation to be of use.

PostgreSQL however already provides a number of helper functions which already greatly help with reconstructing DDL and are of course used by this extension. PostgreSQL also has sophisticated query capabilities, such as CTEs and window functions which make this project possible by using only SQL.

Advantages over using other tools like psql or pgdump include:

• You can use it to extract DDL with any client which support running plain SQL queries
• Simple API with just three functions. Just supply oid.
• With SQL you can select things to dump by using usual SQL semantics (WHERE, etc)
• Special function for creating scripts, which drop and recreate entire dependancy trees. This is useful for example, when one wishes to rename some columns in a view with dependants. This works particularly great with transactional DDL of Postgres.
• Created scripts are somewhat more intended to be run and copy/pasted manually by the DBA into other databases/scripts. This involves pretty printing, using idempotent DDL where possible (preferring ALTER to CREATE), creating indexes which are part of a constraint with ADD CONSTRAINT and so on.
• No shell access or shell commands with hairy options required (for running pg_dump), just use SELECT and hairy SQL instead!
• It is entrely made out of plain SQL functions so you don't have to install any extra languages, not even PLpgSQL! It runs on plain vanilla Postgres.

Some disadvantages:

• Not all Postgres objects and all options are supported yet. The package provides support for basic user-level objects such as types, classes and functions. All reg* objects and SQL standard compliant stuff is mostly supported, with more fringe stuff still in constuction. The intention for version 1.0 is to support all objects. See ROADMAP for some of what's missing.
• It is not very well tested. While it contains a number of regression tests, these can be hardly considered as proofs of correctness. Be certain there are bugs. Use at your own risk! Do not run generated scripts on production databases without testing them!
• It is kind of slow-ish for complicated dependancy trees

That said, it has still proven quite useful in a many situations and is being used with a number of production databases.

Curently developed and tested on PostgreSQL 10. Included preprocessor adapts the source to target PG version. Tested to install on version 9.1 and later. Some tests might fail on older versions.

Installation

To build and install this module:

make
make install
make install installcheck

or selecting a specific PostgreSQL installation:

make PG_CONFIG=/some/where/bin/pg_config
make PG_CONFIG=/some/where/bin/pg_config install
make PG_CONFIG=/some/where/bin/pg_config installcheck
make PGPORT=5432 PG_CONFIG=/usr/lib/postgresql/10/bin/pg_config clean install installcheck

Make sure you set the connection parameters like PGPORT right for testing.

And finally inside the database:

CREATE EXTENSION ddlx;

It you use multiple schemas, you will need to have variable search_path set appropriately for the extension to work. To make it work with any value of search_path, you can install the extension in the pg_catalog schema:

CREATE EXTENSION ddlx SCHEMA pg_catalog;

This of course requires superuser privileges.

Using

The API provides three public user functions:

• ddlx_create(oid) - builds SQL DDL create statements
• ddlx_drop(oid) - builds SQL DDL drop statements
• ddlx_script(oid) - builds SQL DDL scripts of entire dependancy trees

You can use these simply by casting object name (or oid) to some reg* type. All reg* types are supported:

• ddlx_create(regtype) returns text

  Generates SQL DDL source for type regtype.

• ddlx_create(regclass) returns text

  Generates SQL DDL source of a class (table or view) regclass. This also includes all associated comments, ownership, constraints, indexes, triggers, rules, grants, etc...

• ddlx_create(regproc) returns text

• ddlx_create(regprocedure) returns text

  Generates SQL DDL source of function regproc.

• ddlx_create(regoper) returns text

• ddlx_create(regoperator) returns text

  Generates SQL DDL source of operator regpoper.

• ddlx_create(regrole) returns text

  Generates SQL DDL source for role (user or group) regrole.

• ddlx_create(regconfig) returns text

  Generates SQL DDL source for text search configuration regconfig.

• ddlx_create(regdictionary) returns text

  Generates SQL DDL source for text search dictionary regdictionary.

There is also a convenience function to use oid directly, without casting:

• ddlx_create(oid) returns text

  Generates SQL DDL source for object ID, oid. This is the most general-purpose function of the bunch. It also works for objects other than reg* types specified above.

  For those, you can use something like: sql SELECT ddlx_create(oid) FROM pg_foreign_data_wrapper WHERE fdwname='postgres_fdw';

• ddlx_drop(oid) returns text

  Generates SQL DDL DROP statement for object ID, oid.

There is also a higher level function to build entire DDL scripts. Scripts include dependant objects and can get quite large.

• ddlx_script(oid) returns text

  Generates SQL DDL script for object ID, oid and all it's dependants.

• ddlx_script(text) returns text

  Generates SQL DDL script for object identified by textual sql identifier and all it's dependants.

  This works only for types, including classes such as tables and views and for functions. For a function, argument types need to be specified.

At the begining of a script, there are commented-out DROP statements for all dependant objects, so you can see them easily.

At the end of a script, there are CREATE statements to rebuild dropped dependant objects.

Note that dropping dependant tables will erase all data stored there, so use with care! Scripts might be more useful for rebuilding layers of functions and views and such.

For example:

```sql CREATE TABLE users ( id int PRIMARY KEY, name text );

SELECT ddlx_script('users');

CREATE TYPE my_enum AS ENUM ('foo','bar');

SELECT ddlx_script('my_enum');

SELECT ddlx_script(current_role::regrole);

```

A number of other functions are provided to extract more specific objects. Their names all begin with ddlx_. They are used internally by the extension and are possibly subject to change in future versions of the extension. They are generally not intended to be used by the end user. Nevertheless, some of them are:

• ddlx_identify(oid) returns record

  Identify an object by object ID, oid. This function is used a lot in others.

• ddlx_describe(regclass) returns setof record

  Get columns of a class.

See file ddlx.sql and full list of functions for additional details. Functions with comments are public API. The rest are intended for internal use, the purpose can usually be inferred from the name.

See file function_usage.svg for a picture of how this is put together.