BREAKING CHANGE:
Moves `upload` field and `relationship` fields with `hasMany: false` &
`relationTo: string` from the many-to-many `_rels` join table to simple
columns. This only affects Postgres database users.
## TL;DR
We have dramatically simplified the storage of simple relationships in
relational databases to boost performance and align with more expected
relational paradigms. If you are using the beta Postgres adapter, and
you need to keep simple relationship data, you'll need to run a
migration script that we provide you.
### Background
For example, prior to this update, a collection of "posts" with a simple
`hasMany: false` and `relationTo: 'categories'` field would have a
`posts_rels` table where the category relations would be stored.
This was somewhat unnecessary as simple relations like this can be
expressed with a `category_id` column which is configured as a foreign
key. This also introduced added complexity for dealing directly with the
database if all you have are simple relations.
### Who needs to migrate
You need to migrate if you are using the beta Postgres database adapter
and any of the following applies to you.
- If you have versions enabled on any collection / global
- If you use the `upload` field
- If you have relationship fields that are `hasMany: false` (default)
and `relationTo` to a single category ([has
one](https://payloadcms.com/docs/fields/relationship#has-one)) relations
### We have a migration for you
Even though the Postgres adapter is in beta, we've prepared a predefined
migration that will work out of the box for you to migrate from an
earlier version of the adapter to the most recent version easily.
It makes the schema changes in step with actually moving the data from
the old locations to the new before adding any null constraints and
dropping the old columns and tables.
### How to migrate
The steps to preserve your data while making this update are as follows.
These steps are the same whether you are moving from Payload v2 to v3 or
a previous version of v3 beta to the most recent v3 beta.
**Important: during these steps, don't start the dev server unless you
have `push: false` set on your Postgres adapter.**
#### Step 1 - backup
Always back up your database before performing big changes, especially
in production cases.
#### Step 2 - create a pre-update migration
Before updating to new Payload and Postgres adapter versions, run
`payload migrate:create` without any other config changes to have a
prior snapshot of the schema from the previous adapter version
#### Step 3 - if you're migrating a dev DB, delete the dev `push` row
from your `payload_migrations` table
If you're migrating a dev database where you have the default setting to
push database changes directly to your DB, and you need to preserve data
in your development database, then you need to delete a `dev` migration
record from your database.
Connect directly to your database in any tool you'd like and delete the
dev push record from the `payload_migrations` table using the following
SQL statement:
```sql
DELETE FROM payload_migrations where batch = -1`
```
#### Step 4 - update Payload and Postgres versions to most recent
Update packages, making sure you have matching versions across all
`@payloadcms/*` and `payload` packages (including
`@payloadcms/db-postgres`)
#### Step 5 - create the predefined migration
Run the following command to create the predefined migration we've
provided:
```
payload migrate:create --file @payloadcms/db-postgres/relationships-v2-v3
```
#### Step 6 - migrate!
Run migrations with the following command:
```
payload migrate
```
Assuming the migration worked, you can proceed to commit this change and
distribute it to be run on all other environments.
Note that if two servers connect to the same database, only one should
be running migrations to avoid transaction conflicts.
Related discussion:
https://github.com/payloadcms/payload/discussions/4163
---------
Co-authored-by: James <james@trbl.design>
Co-authored-by: PatrikKozak <patrik@payloadcms.com>
