Volt Introduction and Docs

Store Collection

The store collection backs data in the database. Currently, the only supported database is Mongo. (More coming soon, RethinkDb and Postgres will probably be next). Because store sometimes need to wait for data to come back from the server, all query methods on store return a Promise. If you are new to promises, be sure to read more about Opal's promises before continuing.

In Volt, you can access store on the front-end and the back-end. Data will automatically be synced between the browser and the server. Any changes to the data in store will be reflected on any clients using the data (unless a buffer is in use - see below).

store._items.create({name: 'Item 1'})
# => #<Promise(70297824266280): #<Volt::Model id: "9a46..5dd7", name: "Item 1">>

# => #<Promise(70297821413860): #<Volt::Model id: "9a46..5dd7", name: "Item 1">>

Calling create (or append, or <<) on store._items will create an items table in the data store (if it doesn't exist) and insert the model document into it. A globally unique id will be generated automatically.

Promises on store

In order to support asynchronus loading, methods on store ArrayModels return promises. If you want to work with the results of a query, you can call .then on it.

store._items.first.then do |item|
  # work with item

See here for more information on promises in ruby/opal.

Promises in Bindings

Promises can be passed to bindings and the bindings will update with the value once the promise resolves. This means you can do something like the following:

{{ store._items.first.then {|i| i._name } }}

This would grab the first item, then return its name once it resolves. This also preserves the reactivity, since if the first item changes, it will re-run the binding all together and re-resolve.

Promise Method Forwarding

To make the above example simpler, Volt extends promises so you can call methods directly on the promise and it will call the method on the resolved value once the promise resolved. The following are the semantically the same:

store._items.first.then {|i| i._name }

Promise method forwarding only works on methods not already defined on the Promise class. Currently the following methods are defined on Promise. (The plan is to redo the Promise class at some point to remove most of these)

error, prev, next, value, act?, action, exception?, realized?, resolved?, rejected?, ^, <<, >>, resolve, resolve!, reject, reject!, exception!, then, do, fail, rescue, catch, always, finally, ensure, trace, inspect, method_missing, each, value_or_error, to_json, unwrap, sync

The ones you may run into are .to_json and .inspect

Promise Sync

If you are working with store on the server only (in tasks for example), you can call .sync on a Promise to have it synchronusly resolve and return the result. If the promise is rejected, .sync will raise an error.

# Remember this only works on the server or console

store._items.create({name: 'Item 1'})

# .sync blocks until the items are loaded
# => #<Volt::Model id: "3607..a0b0", name: "Item 1">

# => 1


Currently store persists to a mongodb database. We are working on adding a data provider api that will allow support for any data store. Volt currently supports the following query methods:


.where passes down its arguments to a mongodb .find call.


.limit lets you restrict how many results you want.


.skip says how many items in you want to start fetching. So store._items.skip(5).limit(10) would grab items 5-15.


.order passes its arguments to a mongodb .sort call. Since .sort is already a method on ruby's Enum class, we use .order instead.

Store Model State

Because there is a delay when syncing data to the server, store models provide a loaded_state method that can be used to determine if the model is in the process of loading.

state description
not_loaded data is not loaded
loading model is fetching data from the server
loaded data is loaded and no changes are unsynced
dirty the data was loaded, but it is no longer being kept in sync with the server