utilities:state-transitions

A simplified reactive state transitions engine

Installation

meteor add utilities:state-transitions

Description

This package watches a given property on your documents, and executes a callback when it changes to a specified value.

Note that this is not a full-fledged state machine, but just a way to conditionally execute code when a document's property changes between a set of given values.

Adding Transitions

myCollection.stateTransitions(property, transitions)

• property: String
• transitions: Array of transitions.

This will watch property on every document belonging to the myCollection collection, and whenever it changes check to see if a transition should be triggered.

Transitions have the following properties:

• name: the transition's name.
• from: the start state to match, array of start states, or wildcard (*).
• to: the end state to match, array of start states, or wildcard (*)
• callback(oldDocument, newDocument): the function to execute if the transition is matched.

Note that you should add all your desired transitions before Meteor.startup(), not inside it.

Listing Transitions

Transitions can be accessed as collection.stateTransitions.

Example

Let's suppose posts in our app each have a status property that tracks whether they're approved, pending, rejected, deleted, etc.

Here's how you would increment a category's postsCount property whenever a post belonging to that category is approved, and decrement it whenever that post is unapproved.

By using the * wildcard, we can match transitions between approved and any other possible value for the status property.

Posts = new Mongo.Collection("posts");

Posts.transitions.add("status", [
  {
    name: "approve",
    from: "*",
    to: "approved",
    callback: function (post) {
      Categories.update(post.categoryId, {$inc: {"postsCount": 1}});
    }
  },
  {
    name: "unapprove",
    from: "*",
    to: "approved",
    callback: function (post) {
      Categories.update(post.categoryId, {$inc: {"postsCount": -1}});
    }
  }
]);