Option to use joins instead of multiple calls for relations.

Suggestion

An option to use joins instead of multiple calls for relations would be useful for performance reasons and would also not effect multi datasources setups by default.

Use Cases

We are using a lot of DB calls with nested relations and each of those relations are fetched using extra DB calls which could be avoided. I understand the reasoning behind not using joins but I believe there should at least be an option to include relations through joins when required.

Examples

The syntax could be something like this -

"include": [
{
"relation": "child",
"join": "true"
}
],

or this could be defined at the model level in the relation decorator.

Acceptance criteria

TBD - will be filled by the team.

No files, tests, entry points, or acceptance criteria are named in the issue. Start by reviewing how relation includes and PostgreSQL queries are currently handled, then clarify the join syntax, model-level behavior, multi-datasource constraints, and tests required before implementation can be considered done.