Entity Component System API reference

This page contains an overview of some key APIs that make up Unity's Entity Component System (ECS).

Entity types	Description
Entity	The fundamental identifier in ECS.
EntityArchetype	A unique combination of component types. For more information, see Archetype concepts.
EntityQuery	Select entities with specific characteristics. For more information, see Querying entity data with an entity query.
EntityQueryBuilder	Create EntityQuery objects.
EntityManager	Manages entities and provides utility methods.
World	An isolated collection of entities. For more information see World concepts

Component types	Description
IComponentData	A marker interface for general purpose components.
ISharedComponentData	A marker interface for components that more than one entity shares. For moe information, see Shared components.
ICleanupComponentData	A marker interface for specialized system components. For more information, see Cleanup components.
IBufferElementData	A marker interface for buffer elements. For more information, see Buffer components.
DynamicBuffer	Access buffer elements.
BlobAssetReference	A reference to a blob asset in a component.

System types	Description
ISystem	An interface to create systems from.
ComponentSystemBase	Defines a set of basic functionality for systems. For more information, see Creating systems with SystemBase.
SystemBase	The base class to extend when writing a system.
ComponentSystemGroup	A group of systems that update as a unit. For more information, see System groups.

ECS job types	Description
IJobEntity	An interface to implicitly create a job that iterates over the entities. For more information, see Iterate over component data with IJobEntity.
Entities.ForEach	An implicitly created job that iterates over a set of entities. For more information, see Iterate over data with Entities.ForEach.
Job.WithCode	An implicitly created single job.
IJobChunk	An interface to explicitly create a job that iterates over the chunks matched by an entity query. For more information, see Iterate over data with IJobChunk.

Other important types	Description
ArchetypeChunk	The storage unit for entity components.
EntityCommandBuffer	A buffer for recording entity modifications used to reduce structural changes. For more information see Scheduling data changes with an EntityCommandBuffer.
ComponentType	Define types when creating entity queries.
BlobBuilder	A utility class to create blob assets, which are immutable data structures that can be safely shared between jobs using BlobAssetReference instances.
ICustomBootstrap	An interface to implement to create your own system loop.
SystemAPI	Class that gives access to access to buffers, components, time, enumeration, singletons and more. This also includes any IAspect, IJobEntity, SystemBase, and ISystem.

Attributes	Description
UpdateInGroup	Defines the ComponentSystemGroup that a system should be added to.
UpdateBefore	Specifies that one system must update before another.
UpdateAfter	Specifies that one system must update after another
DisableAutoCreation	Prevents a system from being automatically discovered and run when your application starts up
ExecuteAlways	Specifies that a system's update function must be invoked every frame, even when no entities are returned by the system's entity query.