Support required relation constraints in schema

[uriva]

Problem

It would be useful if Instant schema could express that a relation is required, so application data can rely on that invariant being enforced by the database layer.

Today, even when an app models a one-to-one or one-to-many link as conceptually mandatory, the relation can still be unset. That means applications need to enforce the invariant entirely in application code and periodically audit or repair missing links.

Feature request

Add support for required relation constraints in the schema.

Examples of the kind of guarantees that would be helpful:

• a one-link that must always be present
• a relation with a minimum cardinality, such as at least one linked record
• validation on writes so invalid states are rejected instead of silently accepted

Why this would help

This would make schema definitions more expressive and reduce a class of data-integrity bugs that are otherwise easy to introduce through alternate write paths, migrations, or manual/admin mutations.

Possible directions

Some possible designs:

• schema-level required support for links
• min / max cardinality constraints on relations
• optional validation tooling that can both block invalid writes and report existing violations

Even a limited first version for required one-links would be very useful.

[nezaj]

We do have a way to set required links in the schema! You can do this both in the explorer and in the schema definition

This will be enforced on the server but the client may still have partial results. This is due to edge cases like when you create a new entity and link it to an existing entity that hasn't been loaded -- right now would optimistically show the new entity and then attach the existing entity once it's loaded from the server. More details here: https://discord.com/channels/1031957483243188235/1488987919996944484/1488992798551179375

[uriva]

So typing wise, we can't get this as "always there"?

[nezaj]

Right now no, we could change the behavior to make it so via filtering out partial results until the server responds but that would be at the expense of the optimistic update and not work offline.

There could be another solution though, we need to think on it more!

[kiluazen]

Your thread on required relation constraints caught my eye. I've been scoping the inspection side of the same problem.

Lens is a schema-aware client for InstantDB. It reads the schema and surfaces relations as first class, including which ones are partial vs filled. One click scopes everything, writes land live.

Not shipping yet but adding user-one slots. The page has a way to ping me if useful.

best,
kushal

[uriva]

@kiluazen lol just send a pr?