Getting component from relationship target

[sashton]

I'm trying to test out a simple scenario for Relationships, but I don't think I've seen mention in the docs or tests what the ideal solution is for getting a component of a relationship target. In my example I am trying to make one entity change direction toward another entity.
Here is a minimal example:

C_Targeting is a tag component with no data.

  # in world setup

  entity_a.add_components([
    C_Transform.new(Vector2(200,200))
  ])

  entity_b.add_components([
    C_Transform.new(Vector2(300,250)),
    C_Velocity.new(Vector2.ZERO)
  ])

  enitity_b.add_relationship(Relationship.new(C_Targeting.new(), entity_a))

Here is the targeting system

class_name TargetTrackingSystem
extends System

func query():
  return (
    q 
    .with_relationship([Relationship.new(C_Targeting.new())]) 
    .with_all([C_Velocity,C_Transform])
  )

@warning_ignore("unused_parameter")
func process(entities: Array[Entity], components: Array, delta: float):
  for entity in entities:
    var c_velocity = entity.get_component(C_Velocity) as C_Velocity
    var c_trs = entity.get_component(C_Transform) as C_Transform
    var rel := entity.get_relationship(Relationship.new(C_Targeting.new()))
    var target: Entity = rel.target as Entity
    

    # QUESTIONABLE ASSUMPTION HERE:
    # getting component from target, which may or may not exist on the entity!
    var c_target_trs = target.get_component(C_Transform) as C_Transform
    

    var vel = c_trs.position.direction_to(c_target_trs.position) * c_velocity.velocity.length()
    c_velocity.velocity = vel

In the system's process function, I need a C_Transform component from the target in order to know which direction to point. But I can't figure out if there is a way to formulate the system query to guarantee that the entity will have a C_Transform at that point. I can see examples of adding an entity in the docs/tests, but I don't see any examples of using that target entity further, like reading from one of its components. Is there a way to handle this without just assuming a component will be present?

[csprance]

You can the matches function against the entities.

So if you create a query

var ents_with_c_transform = ECS.world.query.with_all([C_Transform]).matches(list_of_entities)

Those entities are guaranteed to have what is defined in the query