The Entity.prerequisites() method is, in fact, very straightforward to use. After an entity is initialised, alongside its properties, but before the onEnterWorld() method is called, the EntityManager class calls the prerequisites() method on the entity. The method must return a list of all assets that must be loaded before the entity enters the world.

A simple example is illustrated below:

class TradeKiosk( BigWorld.Entity ):
  MODEL = 'models\kiosk.model'

  def prerequisites( self ):
    # return list even if it is just a single file
    return [ TradeKiosk.MODEL ]

  def onEnterWorld( self, prerequisites ):
    self.model = prerequisites[ TradeKiosk.MODEL ]

Simple example of loading prerequisite assets

A more realistic scenario is when the required resources vary according to the entity state. In this case, a single entity type is used to model all types of pickable flowers. The type property is used to differentiate each instance. Since type is guaranteed to be initialised when the prerequisites method is called, the script can customise which resources are loaded. In this case, the type property will not change over the lifetime of this particular entity, so we only need to load resource once.

class PickableFlower( BigWorld.Entity ):
  ASSETS = {
    'lili' : ('models\lili.model', 'effects\sparkles.xml')
    'daisy' : ('models\daisy.model', 'effects\spirits.xml')
    'orchid' : ('models\orchid.model', 'effects\petals.xml')
  }

  PICK_SOUND = 'sounds\pick_flower.wav'

  def prerequisites( self ):
    prereq = []
    prereq.append(PickableFlower.ASSETS[self.type][0])
    prereq.append(PickableFlower.ASSETS[self.type][1])
    prereq.append(PickableFlower.PICK_SOUND)
    return prereq

  def onEnterWorld( self, prerequisites ):
    # model varies according to the type of flower.
    # prerequisites can be accessed like a map, and returns python objects.
    # in this case, we know that .model files become PyModels.
    self.model = prerequisites[ PickableFlower.ASSETS[self.type][0] ]
    
    # it is up to us whether or not to hold onto the PyResourceRefs instance
    # passed into onEnterWorld.  In this case, we will be using the particle
    # system at a later date, so we'll simply hold onto the object until it
    # is needed.
    self.prerequisites = prerequisites

  def onPickEvent( self ):
    # picking sound effect is constant between types
    self.model.playSound( PickableFlower.PICK_SOUND )

    # particle effect varies according to the type of flower
    particles = self.prerequisites[ PickableFlower.ASSETS[self.type][1] ]
    self.model.root.attach( particles )
    particles.force(1)

Another example of load prerequisite assets