Add support for Postgres GENERATED ALWAYS AS IDENTITY

[mdurling]

Feature Description

The Problem

A recent feature added Postgres support for identity columns { generated: 'identity' } which will generate columns using GENERATED BY DEFAULT AS IDENTITY. It would be great to support the option to generate columns using GENERATED ALWAYS AS IDENTITY.

The Solution

We currently use { insert: false } column option so that Typeorm won't include the identity column in the INSERT statements for some existing tables we have whose identity column was previously created with GENERATED ALWAYS AS IDENTITY.

It would be nice to be able to have Typeorm use GENERATE ALWAYS AS IDENTITY or GENERATE BY DEFAULT AS IDENTITY based on some option. The insert option is not included in TableColumnOptions so that would not appear to be useful as a solution for conditionally generating the proper migration code.

Relevant Database Driver(s)

DB Type	Relevant
aurora-data-api	no
aurora-data-api-pg	no
better-sqlite3	no
cockroachdb	no
cordova	no
expo	no
mongodb	no
mysql	no
nativescript	no
oracle	no
postgres	yes
react-native	no
sap	no
sqlite	no
sqlite-abstract	no
sqljs	no
sqlserver	no

Are you willing to resolve this issue by submitting a Pull Request?

• ✖️ Yes, I have the time, and I know how to start.
• ✖️ Yes, I have the time, but I don't know how to start. I would need guidance.
• ✖️ No, I don’t have the time, but I can support (using donations) development.
• ✅ No, I don’t have the time and I’m okay to wait for the community / maintainers to resolve this issue.

[leoromanovsky]

We're on the same wavelength @drtyh2o - mentioned this the other day in TypeORM's Slack and seems like there is support from the Maintainer to go in this direction: https://typeorm.slack.com/archives/CCTEVJC8G/p1636621370078900

How did you create and manage your tables with an identity before the feature was added?

[mdurling]

How did you create and manage your tables with an identity before the feature was added?

We used generated: ‘increment’ and modified the migration manually. It was super tedious (especially on subsequent migrations as typeorm always wanted to change it back). The new generated: ‘identity’ is a huge improvement. The ability to optionally use GENERATED ALWAYS AS IDENTITY would be most welcome.

Feel free to expand and use this issue (or close it in favor of a new one) should you decide to pursue a contribution.