Base objects

Database is the root object of Watermelon. It owns:

  • a DatabaseAdapter
  • a map of Collections

DatabaseAdapter connects Watermelon's reactive world to low-level imperative world of databases. See Adapters.

Collection manages all records of a given kind:

  • it has a cache of records already fetched from the database (RecordCache)
  • it has the public API to find, query and create existing records
  • it implements fetch/update/delete operations on records

Model is an instance of a collection record. A model class describes a kind of a record. Model is the base class for your concrete models (e.g. Post, Comment, Task):

  • it describes the specific instance - id + all custom fields and actions
  • it has public API to update, markAsDeleted and destroyPermanently
  • implements record-level observation observe()
  • static fields describe base information about a model (table, associations) - See Defining models

As a general rule, Model manages the state of a specific instance, and Collection of the entire collection of records. So for example, model.markAsDeleted() changes the local state of called record, but then delegates to its collection to notify collection observers and actually remove from the database

Query is a helper object that gives us a nice API to perform queries (query.observe(), query.fetchCount()):

  • created via collection.query()
  • encapsulates a QueryDescription structure which actually describes the query conditions
  • fetch/observe methods actually delegate to Collection to perform database operations
  • caches Observables created by observe/observeCount methods so they can be reused and shared

Helper functions

Watermelon's objects and classes are meant to be as minimal as possible — only manage their own state and be an API for your app. Most logic should be stateless, and implemented as pure functions:

QueryDescription is a structure (object) describing the query, built using Q.* helper functions

encodeMatcher(), simpleObserver(), reloadingObserver(), fieldObserver() implement query observation logic (See Observation.)

Model decorators transform simple class properties into Watermelon-aware record fields.

Much of Adapters' logic is implemented as pure functions too. See Adapters.