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.

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

| Aspect | Traditional OOP | ECS/DOTS | | ----------- | ----------------- | --------------- | | Data layout | Object-oriented | Data-oriented | | Memory | Scattered | Contiguous | | Processing | Per-object | Batched | | Scaling | Poor with count | Linear scaling | | Best for | Complex behaviors | Mass simulation |

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();
    }

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

        // Simple foreach - auto-generates job
        foreach (var (transform, speed) in
            SystemAPI.Query, RefRO>())
        {
            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()
            .WithNone()
            .WithOptions(EntityQueryOptions.FilterWriteGroup)
            .Build(ref state);
    }

    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        // SystemAPI.Query - simplest approach
        foreach (var (health, entity) in
            SystemAPI.Query>()
                .WithAll()
                .WithEntityAccess())
        {
            if (health.ValueRO.Current ()
                    .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(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();
        var ecb = ecbSingleton.CreateCommandBuffer(state.WorldUnmanaged);

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

            if (spawner.ValueRO.Timer  _transform;
    private readonly RefRO _speed;
    private readonly RefRW _health;

    // Optional component
    [Optional]
    private readonly RefRO _shield;

    // Buffer
    private readonly DynamicBuffer _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())
        {
            character.Move(new float3(1, 0, 0), dt);

            if (character.CurrentHealth ();

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

        // Check exists
        if (SystemAPI.HasSingleton())
        {
            // ...
        }
    }
}

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
    {
        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
    {
        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(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 Positions;

    // Thread-safe write to hash map
    public NativeParallelMultiHashMap.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 _hashMap;

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

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

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

        int count = query.CalculateEntityCount();

        // Resize if needed
        if (_hashMap.Capacity (Allocator.TempJob);
        var posFloat3 = new NativeArray(count, Allocator.TempJob);

        for (int i = 0; i  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

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: sherererlock
• Source: sherererlock/UnityDev_ClaudeCode
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.