History Tracking

NOTE

This is functionality is limited to applications using the Solid Protocol.

In some situations, it is desirable to keep track of changes made to a model over time. That is the cornerstone of making local-first applications.

History tracking is disabled by default, but you can enable it in the model declaration:

class Person extends SolidModel {
    static history = true;
}

Once this is enabled, any changes that are made to the model will create new operations using the built-in operations relationship:

const alice = await Person.create({ name: 'Alice' });

await alice.update({ name: 'Alice Doe' });

console.log(alice.operations.length);
// console output: 2

The code above will generate the following operations:

Set name to "Alice"
Set name to "Alice Doe"

This is a trivial example, but this allows implementing a crude CRDT mechanism that uses the Solid POD as mediator. This can be demonstrated by creating two instances of a model, updating them separately, and synchronizing them afterwards using the synchronize method:

// Create two divergent models.
const original = await Person.create({ name: 'Peter Parker', alias: 'Spider-Man' });
const divergent = original.clone({ clean: true });

// Update them independently.
await original.update({ alias: 'The Amazing Spider-Man' });
await divergent.update({ name: 'Miles Morales' });

// Synchronize updates.
await SolidModel.synchronize(original, divergent);

// Both are now "Miles Morales - The Amazing Spider-Man". 🤔
console.log(original.getAttributes());
console.log(divergent.getAttributes());

There are also other use-cases supported, such as soft-deletes (marking a resource as deleted even though it still exists), and tombstones (leaving a crdt:Tombstone resource behind instead of deleting the entire document).

If you want to learn more about CRDTs in Solid, check out the following presentation:

History Tracking ​

History Tracking