Building for Electric

Electric maintains a fork of the original because we need a few tweaks on the upstream behaviour, specifically:

  • Set column defaults within the CREATE TABLE (...) block, rather than via ALTER TABLE .. SET DEFAULT statements after the table creation.

  • Define table constraints within the create table block too

Both of these are to support direct PostgreSQL -> SQLite command translation. For example, SQLite does not support ALTER TABLE .. SET DEFAULT and we are currently very strict about the migrations that we allow on electrified tables.

So it’s best for our use case that tables are created in one shot, without additional ALTER TABLE commands.

As PG versions progress it may be necessary to update these functions, hence this fork which applies our patches in the ddlx.sql file which has pre-processor statements for multiple PG version support.

Generating Electric extension SQL

For the purposes of Electric, “extension” does not mean a postgresql extension. Electric has its own extension mechanism based on simple SQL statements, maintained via a basic migration system.

That extension mechanism expects everything to be written within the electric pg schema. PostgreSQL allows for extensions to be relocated into any schema via the built-in extension mechanism. Since we can’t use that, we need to be able to write our functions into a specific schema.

So we have a pre-processor script that prefixes all function definitions and calls with a @schemaname@ prefix which we can replace when applying the sql to the live pg database.

To generate a new “electrified” ddlx script, run the following:

make electric VERSION=$PG_VERSION

This will write a processed file to electric-ddlx-$PG_VERSION.sql in this repo.

This file should be moved into the electric repo somewhere under components/electric/lib/electric/postgres/extension/migrations/$TIMESTAMP/ddlx-$PG_VERSION.sql. See the existing ddlx migration version for a template.