Forums » Impact Engine » Confused about ig.game.getEntitiesByType

Let's say I create a entity called EntityParent, then another entity that extends EntityParent called EntityChild.

When I call ig.game.getEntitiesByType(EntityParent), I get both EntityParent and EntityChild instances. I was expecting to get only EntityParent instances.

Assuming that that is normal behavior, how does one get just EntityParent instances?

Yes, that is expected behavior. getEntitiesByType() uses JavaScript&039;s #instanceof operator – so an instance of EntityChild is actually of the type EntityParent, ig.Entity and Object as well. I should really have made this more clear in the documentation. Sorry.

There is no built-in function that does what you want, though. You'll have to check for a certain property (that only one of those two classes has) by yourself.

Depending on how many entities you have, it would maybe also make sense to have several arrays of entities in your Game and add entities to these lists in their init() method.

I ended up sorting the array of parent entities by their id's, then grabbing the first.

I suspect this might be brittle, but from what I can see my parent entity always has the lowest numbered ID. If that fails, I'll consider detecting a unique-to-the-parent property.

For those curious, here's how I grab the first one:

function compare(a,b) {
  return (a.id - b.id);
}
      
var parentEntities = this.getEntitiesByType(EntityParent);
this.parent = parentEntities.sort(compare)[0];

The IDs of entities are assigned in their order of creation. So if you spawn an EntityChild first and an EntityParent after that, the EntityChild will have the lower id.

If you just need to get one entity anyway, consider giving this entity a name and use the getEntityByName() method.

I actually tried using getEntityByName() first without success. Giving an entity a property of name, either in the constructor or after instantiation didn't change what ig.game.getEntityByName returned (which was always undefined).

Can you verify that it's working?

Assigning a name after instantiation will have no effect, because it is only looked at once, during spawnEntity(). So either set the name as a class property (if you only ever will have one single instance of that entity) or set in the entity&039;s #init() method.

There was also a bug in 1.14 causing it to ignore an entity&039;s name completely when it was not set in Weltmeister (i.e. through the #settings object). See the changelog. Again... sorry for that :/

There was also a bug in 1.14

That explains a lot. I'm still on 1.14. I'll grab the latest and use getEntityByName().

I've upgraded to 1.15 and the only time I'm able to get getEntityByName to return anything is when I spawn an entity with a settings object like so:

So this works:

ig.game.spawnEntity(EntityNpc, 24,24, {name: "first_npc"});
ig.game.getEntityByName("first_npc"); // returns what we just spawned

getEntityByName doesn&039;t return objects with a class property with a certain name. #getEntityByName doesn&039;t return objects after adding a #name property to the settings object within an entity&039;s #init method.

I don&039;t mind class properties not playing nice, but setting the name within init would be quite nice. Especially since a lot of my NPCs are loaded as part of a level and all the entity spawning is happening deep within #loadLevel.

Could you show me a working example of setting the name within init just in case I'm doing it wrong?

Are you sure you are using the 1.15 sources? It sounds like you&039;re still having the bug from 1.14. Please check if your #lib/impact/game.js file reads the following on lines 86-91:

	var ent = new (entityClass)( x, y, settings || {} );
	this.entities.push( ent );
	if( ent.name ) {
		this.namedEntities[ent.name] = ent;
	}
	return ent;

There's not much to do wrong when setting the name. Something like this for your entity should be perfectly fine:

init: function( x, y, settings ) {
	this.parent( x, y, settings );
	this.name = 'first_npc';
},

Well, I thought I had the 1.15 source, but I had a git configuration issue and hadn't pulled the latest game.js for some reason. I'm up to date now and all is well.