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Storage

Adapters:

How we determine which adapter to use

We determine the storage adapter here.

The Storage class

  • The Storage class is what interacts with the adapters.

Storage Adapters

  1. There is one adapter per database type we support (i.e. three adapters).
  2. Each adapter provides a unified API for the storage engine to interact with.
  3. The SQLite adapter lives in it’s own package.
  4. ExclusiveStorage wraps public storage methods (e.g. Storage.runExclusive)
    1. Guarantees consistency
    2. Makes the storage class transactional
    3. Provides concurrency control

How DataStore finds records locally:

  • Varies by storage adapter
  • SQLiteAdapter: DataStore constructs a query.
  • Async Storage: DataStore scans and filters.
  • IndexedDB: if the query is by primary key, DataStore queries against the index, otherwise it scans and filters.
    • Note: The lazy loading branch includes an improvement to the IndexedDB adapter that will check if any search criteria can leverage an index (there is no preference for low cardinality; the first identified index is used.) If so, the base result is sourced from the index and the remaining criteria will be applied as a filter.

Understanding the difference between Save and Batch Save

  • As the names imply, save accepts a single record and persists it, while batchSave accepts a page of records and persists them all. batchSave, however, is only used within the sync processor, and will filter out deleted records from the sync page results, and then delete them from the local db.