ViewModelCache

Cache for ViewModel instances based on the specified field names set.

The key to the cache is the primary key for the record and the field names set on it. For example if you have a record that accepts id, name and email you could have a record cached for id, for name, for email or any combination of the 3 fields. This is to handle the common case of fetching partial data from a backend.

The cache implementation will update any cache entries that are a subset of a new cache entry. eg. Caching a record with all the possible fields set would result in all the existing partial field cache entries being updated to match the data on the full record for the fields it care about.

Usage:

// Assume User is a ViewModel already defined
// Add a record
User.cache.add(new User({ id: 1, name: 'John' }));
// Retrieve a record
const record = User.cache.get(1, ['id', 'name']);
// To update a record just add it again
User.cache.add(new User({ id: 1, name: 'Johnny' }));
// Cache is per unique set of fields but a superset will update a subset
User.cache.add(new User({ id: 1, name: 'Johnny Smith', email: 'johnny@test.com' }));
User.cache.get(1, ['id', 'name']);
// { id: 1, name: 'Johnny Smith' }
User.cache.get(1, ['id', 'name', 'email'])
// { id: 1, name: 'Johnny Smith', email: 'johnny@test.com' }
// Delete a specific cache for a subset of fields
User.cache.delete(1, ['id', 'name']);
User.cache.get(1, ['id', 'name']);
// null
User.cache.get(1, ['id', 'name', 'email'])
// { id: 1, name: 'Johnny Smith', email: 'johnny@test.com' }
// Or all fields
User.cache.delete(1);
User.cache.get(1, ['id', 'name', 'email'])
// null
// You can add multiple values at a time
User.cache.addList([johnny, sam]);
// You can listen to changes
User.cache.addListener(2, ['id', 'name'], (previous, next) => console.log(previous, 'change to', next));
User.cache.add(new User({ id: 2, name: 'Bob' }));
// null changed to User({ id: 2, name: 'Bob' })
User.cache.add(new User({ id: 2, name: 'Bobby' }));
// User({ id: 2, name: 'Bob' }) changed to User({ id: 2, name: 'Bobby' })
User.cache.delete(2)
// User({ id: 2, name: 'Bobby' }) changed to null
// You can listen to multiple changes. If you use this and addList then you only get one
// call for each change that occurs within addList
User.cache.addListenerList(
 // Ids to listen for changes to
 [3, 4],
 // Only get updates for cached records with these field names
 ['id', 'name'],
 (previous, next) => console.log(previous, 'change to', next)
);
User.cache.addList([new User({ id: 3, name: 'Jay' }), new User({ id: 4, name: 'Bee' })]);
// [null, null] changed to [new User({ id: 3, name: 'Jay' }), new User({ id: 4, name: 'Bee' })]
User.cache.addList([new User({ id: 3, name: 'Jayz' }), new User({ id: 4, name: 'Beeb' })]);
// [new User({ id: 3, name: 'Jay' }), new User({ id: 4, name: 'Bee' })] changed to [new User({ id: 3, name: 'Jayz' }), new User({ id: 4, name: 'Beeb' })]
User.cache.delete(3)
// [new User({ id: 3, name: 'Jayz' }), new User({ id: 4, name: 'Beeb' })] changed to [null, new User({ id: 4, name: 'Beeb' })]

If a model has a RelatedViewModelField the data for a related field can be retrieved using array notation:

// Fetch the 'name' field and the related 'group' record and its 'label' field
['name', ['group', 'label']]

To fetch all fields from a relation you can just specify its name:

['name', 'group']
// This will be expanded to include all non-relation fields on the related ViewModel
['name', ['group', 'label'], ['group', 'ownerId']]

NOTE: Using the shorthand for a relation won't include any nested relation

Accessing deeply related records is supported:

['name', ['group', 'owner', 'name']]

You can combine the shorthand with array notation to get all fields and the specified deep relations:

['name', 'group', ['group', 'owner', 'name']]
// Equivalent to:
['name', ['group', 'label'], ['group', 'owner', 'name']]

NOTE: When accessing a relation its sourceFieldName is always included regardless of whether you explicitly request it:

User.cache.get(1, ['name', 'group']);
// {
//   id: 1,
//   name: 'Bob',
//   groupId: 1,
//   group: {
//      id: 1,
//      label: 'Staff',
//   }
// }