Milestone adapters

1. Available adapters
   1. ShareDBMilestoneMongo
2. Usage
3. Requesting snapshots

The milestone adapter is responsible for storing periodic snapshots of documents, primarily in order to speed up document history.

Available adapters

ShareDBMilestoneMongo

sharedb-milestone-mongo runs on MongoDB.

Usage

An instance of a milestone adapter should be provided to the Backend() constructor’s milestoneDb option:

const backend = new Backend({
  milestoneDb: new ShareDBMilestoneMongo(),
})

Requesting snapshots

Adapters will define default snapshot behaviour. However, this logic can be overridden using the saveMilestoneSnapshot option in middleware.

Setting context.saveMilestoneSnapshot to true will request a snapshot be saved, and setting it to false means a snapshot will not be saved.

If context.saveMilestoneSnapshot is left to its default value of null, it will assume the default behaviour defined by the adapter.

shareDb.use('commit', (context, next) => {
  switch (context.collection) {
    case 'foo':
      // Save every 100 versions for collection 'foo'
      context.saveMilestoneSnapshot = context.snapshot.v % 100 === 0;
      break;
    case 'bar':
    case 'baz':
      // Save every 500 versions for collections 'bar' and 'baz'
      context.saveMilestoneSnapshot = context.snapshot.v % 500 === 0;
      break;
    default:
      // Don't save any milestones for collections not named here.
      context.saveMilestoneSnapshot = false;
  }

  next();
});