Unity Ecs Patterns

Unity ECS Patterns

Production patterns for Unity's Data-Oriented Technology Stack (DOTS) including Entity Component System, Job System, and Burst Compiler.

Use this skill when

• Building high-performance Unity games
• Managing thousands of entities efficiently
• Implementing data-oriented game systems
• Optimizing CPU-bound game logic
• Converting OOP game code to ECS
• Using Jobs and Burst for parallelization

Do not use this skill when

• The task is unrelated to unity ecs patterns
• You need a different domain or tool outside this scope

Instructions

• Clarify goals, constraints, and required inputs.
• Apply relevant best practices and validate outcomes.
• Provide actionable steps and verification.
• If detailed examples are required, open resources/implementation-playbook.md.

Resources

• resources/implementation-playbook.md for detailed patterns and examples.

Unity ECS Patterns Implementation Playbook

This file contains detailed patterns, checklists, and code samples referenced by the skill.

Unity ECS Patterns

Production patterns for Unity's Data-Oriented Technology Stack (DOTS) including Entity Component System, Job System, and Burst Compiler.

When to Use This Skill

• Building high-performance Unity games
• Managing thousands of entities efficiently
• Implementing data-oriented game systems
• Optimizing CPU-bound game logic
• Converting OOP game code to ECS
• Using Jobs and Burst for parallelization

Core Concepts

1. ECS vs OOP

2. DOTS Components

Entity: Lightweight ID (no data)
Component: Pure data (no behavior)
System: Logic that processes components
World: Container for entities
Archetype: Unique combination of components
Chunk: Memory block for same-archetype entities

Patterns

Pattern 1: Basic ECS Setup

using Unity.Entities;
using Unity.Mathematics;
using Unity.Transforms;
using Unity.Burst;
using Unity.Collections;

// Component: Pure data, no methods
public struct Speed : IComponentData
{
    public float Value;
}

public struct Health : IComponentData
{
    public float Current;
    public float Max;
}

public struct Target : IComponentData
{
    public Entity Value;
}

// Tag component (zero-size marker)
public struct EnemyTag : IComponentData { }
public struct PlayerTag : IComponentData { }

// Buffer component (variable-size array)
[InternalBufferCapacity(8)]
public struct InventoryItem : IBufferElementData
{
    public int ItemId;
    public int Quantity;
}

// Shared component (grouped entities)
public struct TeamId : ISharedComponentData
{
    public int Value;
}

Pattern 2: Systems with ISystem (Recommended)

using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;
using Unity.Burst;

// ISystem: Unmanaged, Burst-compatible, highest performance
[BurstCompile]
public partial struct MovementSystem : ISystem
{
    [BurstCompile]
    public void OnCreate(ref SystemState state)
    {
        // Require components before system runs
        state.RequireForUpdate<Speed>();
    }

    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        float deltaTime = SystemAPI.Time.DeltaTime;

        // Simple foreach - auto-generates job
        foreach (var (transform, speed) in
            SystemAPI.Query<RefRW<LocalTransform>, RefRO<Speed>>())
        {
            transform.ValueRW.Position +=
                new float3(0, 0, speed.ValueRO.Value * deltaTime);
        }
    }

    [BurstCompile]
    public void OnDestroy(ref SystemState state) { }
}

// With explicit job for more control
[BurstCompile]
public partial struct MovementJobSystem : ISystem
{
    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        var job = new MoveJob
        {
            DeltaTime = SystemAPI.Time.DeltaTime
        };

        state.Dependency = job.ScheduleParallel(state.Dependency);
    }
}

[BurstCompile]
public partial struct MoveJob : IJobEntity
{
    public float DeltaTime;

    void Execute(ref LocalTransform transform, in Speed speed)
    {
        transform.Position += new float3(0, 0, speed.Value * DeltaTime);
    }
}

Pattern 3: Entity Queries

[BurstCompile]
public partial struct QueryExamplesSystem : ISystem
{
    private EntityQuery _enemyQuery;

    public void OnCreate(ref SystemState state)
    {
        // Build query manually for complex cases
        _enemyQuery = new EntityQueryBuilder(Allocator.Temp)
            .WithAll<EnemyTag, Health, LocalTransform>()
            .WithNone<Dead>()
            .WithOptions(EntityQueryOptions.FilterWriteGroup)
            .Build(ref state);
    }

    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        // SystemAPI.Query - simplest approach
        foreach (var (health, entity) in
            SystemAPI.Query<RefRW<Health>>()
                .WithAll<EnemyTag>()
                .WithEntityAccess())
        {
            if (health.ValueRO.Current <= 0)
            {
                // Mark for destruction
                SystemAPI.GetSingleton<EndSimulationEntityCommandBufferSystem.Singleton>()
                    .CreateCommandBuffer(state.WorldUnmanaged)
                    .DestroyEntity(entity);
            }
        }

        // Get count
        int enemyCount = _enemyQuery.CalculateEntityCount();

        // Get all entities
        var enemies = _enemyQuery.ToEntityArray(Allocator.Temp);

        // Get component arrays
        var healths = _enemyQuery.ToComponentDataArray<Health>(Allocator.Temp);
    }
}

Pattern 4: Entity Command Buffers (Structural Changes)

// Structural changes (create/destroy/add/remove) require command buffers
[BurstCompile]
[UpdateInGroup(typeof(SimulationSystemGroup))]
public partial struct SpawnSystem : ISystem
{
    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        var ecbSingleton = SystemAPI.GetSingleton<BeginSimulationEntityCommandBufferSystem.Singleton>();
        var ecb = ecbSingleton.CreateCommandBuffer(state.WorldUnmanaged);

        foreach (var (spawner, transform) in
            SystemAPI.Query<RefRW<Spawner>, RefRO<LocalTransform>>())
        {
            spawner.ValueRW.Timer -= SystemAPI.Time.DeltaTime;

            if (spawner.ValueRO.Timer <= 0)
            {
                spawner.ValueRW.Timer = spawner.ValueRO.Interval;

                // Create entity (deferred until sync point)
                Entity newEntity = ecb.Instantiate(spawner.ValueRO.Prefab);

                // Set component values
                ecb.SetComponent(newEntity, new LocalTransform
                {
                    Position = transform.ValueRO.Position,
                    Rotation = quaternion.identity,
                    Scale = 1f
                });

                // Add component
                ecb.AddComponent(newEntity, new Speed { Value = 5f });
            }
        }
    }
}

// Parallel ECB usage
[BurstCompile]
public partial struct ParallelSpawnJob : IJobEntity
{
    public EntityCommandBuffer.ParallelWriter ECB;

    void Execute([EntityIndexInQuery] int index, in Spawner spawner)
    {
        Entity e = ECB.Instantiate(index, spawner.Prefab);
        ECB.AddComponent(index, e, new Speed { Value = 5f });
    }
}

Pattern 5: Aspect (Grouping Components)

using Unity.Entities;
using Unity.Transforms;
using Unity.Mathematics;

// Aspect: Groups related components for cleaner code
public readonly partial struct CharacterAspect : IAspect
{
    public readonly Entity Entity;

    private readonly RefRW<LocalTransform> _transform;
    private readonly RefRO<Speed> _speed;
    private readonly RefRW<Health> _health;

    // Optional component
    [Optional]
    private readonly RefRO<Shield> _shield;

    // Buffer
    private readonly DynamicBuffer<InventoryItem> _inventory;

    public float3 Position
    {
        get => _transform.ValueRO.Position;
        set => _transform.ValueRW.Position = value;
    }

    public float CurrentHealth => _health.ValueRO.Current;
    public float MaxHealth => _health.ValueRO.Max;
    public float MoveSpeed => _speed.ValueRO.Value;

    public bool HasShield => _shield.IsValid;
    public float ShieldAmount => HasShield ? _shield.ValueRO.Amount : 0f;

    public void TakeDamage(float amount)
    {
        float remaining = amount;

        if (HasShield && _shield.ValueRO.Amount > 0)
        {
            // Shield absorbs damage first
            remaining = math.max(0, amount - _shield.ValueRO.Amount);
        }

        _health.ValueRW.Current = math.max(0, _health.ValueRO.Current - remaining);
    }

    public void Move(float3 direction, float deltaTime)
    {
        _transform.ValueRW.Position += direction * _speed.ValueRO.Value * deltaTime;
    }

    public void AddItem(int itemId, int quantity)
    {
        _inventory.Add(new InventoryItem { ItemId = itemId, Quantity = quantity });
    }
}

// Using aspect in system
[BurstCompile]
public partial struct CharacterSystem : ISystem
{
    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        float dt = SystemAPI.Time.DeltaTime;

        foreach (var character in SystemAPI.Query<CharacterAspect>())
        {
            character.Move(new float3(1, 0, 0), dt);

            if (character.CurrentHealth < character.MaxHealth * 0.5f)
            {
                // Low health logic
            }
        }
    }
}

Pattern 6: Singleton Components

// Singleton: Exactly one entity with this component
public struct GameConfig : IComponentData
{
    public float DifficultyMultiplier;
    public int MaxEnemies;
    public float SpawnRate;
}

public struct GameState : IComponentData
{
    public int Score;
    public int Wave;
    public float TimeRemaining;
}

// Create singleton on world creation
public partial struct GameInitSystem : ISystem
{
    public void OnCreate(ref SystemState state)
    {
        var entity = state.EntityManager.CreateEntity();
        state.EntityManager.AddComponentData(entity, new GameConfig
        {
            DifficultyMultiplier = 1.0f,
            MaxEnemies = 100,
            SpawnRate = 2.0f
        });
        state.EntityManager.AddComponentData(entity, new GameState
        {
            Score = 0,
            Wave = 1,
            TimeRemaining = 120f
        });
    }
}

// Access singleton in system
[BurstCompile]
public partial struct ScoreSystem : ISystem
{
    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        // Read singleton
        var config = SystemAPI.GetSingleton<GameConfig>();

        // Write singleton
        ref var gameState = ref SystemAPI.GetSingletonRW<GameState>().ValueRW;
        gameState.TimeRemaining -= SystemAPI.Time.DeltaTime;

        // Check exists
        if (SystemAPI.HasSingleton<GameConfig>())
        {
            // ...
        }
    }
}

Pattern 7: Baking (Converting GameObjects)

using Unity.Entities;
using UnityEngine;

// Authoring component (MonoBehaviour in Editor)
public class EnemyAuthoring : MonoBehaviour
{
    public float Speed = 5f;
    public float Health = 100f;
    public GameObject ProjectilePrefab;

    class Baker : Baker<EnemyAuthoring>
    {
        public override void Bake(EnemyAuthoring authoring)
        {
            var entity = GetEntity(TransformUsageFlags.Dynamic);

            AddComponent(entity, new Speed { Value = authoring.Speed });
            AddComponent(entity, new Health
            {
                Current = authoring.Health,
                Max = authoring.Health
            });
            AddComponent(entity, new EnemyTag());

            if (authoring.ProjectilePrefab != null)
            {
                AddComponent(entity, new ProjectilePrefab
                {
                    Value = GetEntity(authoring.ProjectilePrefab, TransformUsageFlags.Dynamic)
                });
            }
        }
    }
}

// Complex baking with dependencies
public class SpawnerAuthoring : MonoBehaviour
{
    public GameObject[] Prefabs;
    public float Interval = 1f;

    class Baker : Baker<SpawnerAuthoring>
    {
        public override void Bake(SpawnerAuthoring authoring)
        {
            var entity = GetEntity(TransformUsageFlags.Dynamic);

            AddComponent(entity, new Spawner
            {
                Interval = authoring.Interval,
                Timer = 0f
            });

            // Bake buffer of prefabs
            var buffer = AddBuffer<SpawnPrefabElement>(entity);
            foreach (var prefab in authoring.Prefabs)
            {
                buffer.Add(new SpawnPrefabElement
                {
                    Prefab = GetEntity(prefab, TransformUsageFlags.Dynamic)
                });
            }

            // Declare dependencies
            DependsOn(authoring.Prefabs);
        }
    }
}

Pattern 8: Jobs with Native Collections

using Unity.Jobs;
using Unity.Collections;
using Unity.Burst;
using Unity.Mathematics;

[BurstCompile]
public struct SpatialHashJob : IJobParallelFor
{
    [ReadOnly]
    public NativeArray<float3> Positions;

    // Thread-safe write to hash map
    public NativeParallelMultiHashMap<int, int>.ParallelWriter HashMap;

    public float CellSize;

    public void Execute(int index)
    {
        float3 pos = Positions[index];
        int hash = GetHash(pos);
        HashMap.Add(hash, index);
    }

    int GetHash(float3 pos)
    {
        int x = (int)math.floor(pos.x / CellSize);
        int y = (int)math.floor(pos.y / CellSize);
        int z = (int)math.floor(pos.z / CellSize);
        return x * 73856093 ^ y * 19349663 ^ z * 83492791;
    }
}

[BurstCompile]
public partial struct SpatialHashSystem : ISystem
{
    private NativeParallelMultiHashMap<int, int> _hashMap;

    public void OnCreate(ref SystemState state)
    {
        _hashMap = new NativeParallelMultiHashMap<int, int>(10000, Allocator.Persistent);
    }

    public void OnDestroy(ref SystemState state)
    {
        _hashMap.Dispose();
    }

    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        var query = SystemAPI.QueryBuilder()
            .WithAll<LocalTransform>()
            .Build();

        int count = query.CalculateEntityCount();

        // Resize if needed
        if (_hashMap.Capacity < count)
        {
            _hashMap.Capacity = count * 2;
        }

        _hashMap.Clear();

        // Get positions
        var positions = query.ToComponentDataArray<LocalTransform>(Allocator.TempJob);
        var posFloat3 = new NativeArray<float3>(count, Allocator.TempJob);

        for (int i = 0; i < count; i++)
        {
            posFloat3[i] = positions[i].Position;
        }

        // Build hash map
        var hashJob = new SpatialHashJob
        {
            Positions = posFloat3,
            HashMap = _hashMap.AsParallelWriter(),
            CellSize = 10f
        };

        state.Dependency = hashJob.Schedule(count, 64, state.Dependency);

        // Cleanup
        positions.Dispose(state.Dependency);
        posFloat3.Dispose(state.Dependency);
    }
}

Performance Tips

// 1. Use Burst everywhere
[BurstCompile]
public partial struct MySystem : ISystem { }

// 2. Prefer IJobEntity over manual iteration
[BurstCompile]
partial struct OptimizedJob : IJobEntity
{
    void Execute(ref LocalTransform transform) { }
}

// 3. Schedule parallel when possible
state.Dependency = job.ScheduleParallel(state.Dependency);

// 4. Use ScheduleParallel with chunk iteration
[BurstCompile]
partial struct ChunkJob : IJobChunk
{
    public ComponentTypeHandle<Health> HealthHandle;

    public void Execute(in ArchetypeChunk chunk, int unfilteredChunkIndex,
        bool useEnabledMask, in v128 chunkEnabledMask)
    {
        var healths = chunk.GetNativeArray(ref HealthHandle);
        for (int i = 0; i < chunk.Count; i++)
        {
            // Process
        }
    }
}

// 5. Avoid structural changes in hot paths
// Use enableable components instead of add/remove
public struct Disabled : IComponentData, IEnableableComponent { }

Best Practices

Do's

• Use ISystem over SystemBase - Better performance
• Burst compile everything - Massive speedup
• Batch structural changes - Use ECB
• Profile with Profiler - Identify bottlenecks
• Use Aspects - Clean component grouping

Don'ts

• Don't use managed types - Breaks Burst
• Don't structural change in jobs - Use ECB
• Don't over-architect - Start simple
• Don't ignore chunk utilization - Group similar entities
• Don't forget disposal - Native collections leak

Resources

• Unity DOTS Documentation
• Unity DOTS Samples
• Burst User Guide