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Listen to a data store event

In this tutorial we will show how to listen to a components data store event.

Component data store

All your components are stored at runtime in a data store that you can access with System Runtime APIs. It sends: - an update event when a component has been updated in the data store, - an insert event when a component has been created in the data store and - a remove event when a component has been deleted from the data store.

Definiera ditt system

Skapa först ett schema som:

• has for name Person
• has a name property

{
  "_id": "eb74b2c8-a1b7-4a08-aa6e-eaf029e2e3f2",
  "_name": "Person",
  "_inherit": [
    "_Component"
  ],
  "name": "property"
}

• skapa sedan en komponent,
• klicka på komponenten för att ändra den,
• change the value of _id to luke,

{
  "_id": "luke",
  "name": ""
}

• then edit the start method of your system and
• lägg till denna kod:

function start() { 
  // hämta komponenten luke
  const luke = this.require('luke');

  // sätt egenskapen name i komponenten till luke
  luke.name('luke');
}

Listen to an update event of the data store

• klicka på knappen importera i det vänstra verktygsfältet,
• en dialogruta visas,
• click on from the library radio button,
• select Listen to components collection events from the proposed systems,
• click on the Compose button,

This system has now been composed in your system.

• on Behaviors tab, click on _Database model (on the right panel under Models),

• click on the update behavior to edit it,
• lägg till denna kod:

function update(event) { 
  // hämta loggnings-komponenten
  const logger = this. equire('logger');

  // reagerar endast om uppdateringen sker på Person
  om (event.collection === 'Person') {
    logger.info('component' + event.id + ' has for new property ' + event.field + ' : ' + event.value);
  }
}

• spara. Därefter,
• kör ditt system.

Du kommer att se ett meddelande som berättar att egenskapen för komponenten har ändrats.

A system makes a lot of update on the data store when running, so for performance reason always filter on a specific collection.