Entitias Collisions

BaseCollisionSystem.cs

using Entitas;
using System.Collections.Generic;

public abstract class CollisionSystem : ReactiveSystem<InputEntity>
{
    protected Contexts _contexts;

    public CollisionSystem(Contexts contexts) : base(contexts.input)
    {
        _contexts = contexts;
    }

    protected override ICollector<InputEntity> GetTrigger(IContext<InputEntity> context)
    {
        return context.CreateCollector(InputMatcher.Collision);
    }

    protected override bool Filter(InputEntity entity)
    {
        if (!entity.hasCollision) return false;
        return Filter(entity.collision.self, entity.collision.other);
    }

    protected abstract bool Filter(GameEntity self, GameEntity other);

    protected override void Execute(List<InputEntity> entities)
    {
        foreach (var e in entities)
            Execute(e.collision.self, e.collision.other);        
    }

    protected abstract void Execute(GameEntity self, GameEntity other);
}

CollisionComponent.cs

[Input, Cleanup(CleanupMode.DestroyEntity)]
public sealed class CollisionComponent : IComponent
{
    public GameEntity self;
    public GameEntity other;
}

Helpers.cs

using UnityEngine;

public static class EntitasUnityHelpers
{
    public static bool GetEntity(this GameObject go, out GameEntity entity)
    {
        entity = null;
        var view = go.GetComponent<IView>();
        if (view == null || view.Entity == null || !view.Entity.isEnabled) return false;
        entity = view.Entity;
        return true;
    }    
}

PlayerCollisionWithSceneExitSystem.cs

public class PlayerCollisionWithSceneExitSystem : CollisionSystem
{
    public PlayerCollisionWithSceneExitSystem(Contexts contexts) : base(contexts)
    {
    }

    protected override bool Filter(GameEntity self, GameEntity other)
    {
        return self.hasSceneExit && other.isPlayer; 
    }

    protected override void Execute(GameEntity self, GameEntity other)
    {
        _contexts.state.sceneManagerEntity.ReplaceLoadSceneRequest(self.sceneExit.sceneName);
        _contexts.state.sceneManagerEntity.ReplaceSceneEntranceRequest(self.sceneExit.targetEntryPoint);
    }
}

View.cs

// this is the collision-relevant parts of the View monobehaviour
public class View : MonoBehaviour, IView 
{
    public GameEntity Entity {get; set;} // this gets assigned by view service

    protected virtual void OnCollisionEnter2D(Collision2D collision)
    {
        if (Entity == null) return;
        GameEntity otherEntity = null;
        if (collision.gameObject.GetEntity(out otherEntity))
            _contexts.input.CreateEntity().AddCollision(Entity, otherEntity);    
    }
    
    // also add OnTriggerEnter2D in the same way
    // in my games these events are not distinguished from eachother
    
    // ... irrelevant code removed ... 
}

Base collision system, collision component, relevant part of View code to propagate collisions from Unity, example collision system that handles player colliding with scene exit triggers, and a helper to get the entity from the gameobject.