Entity Component System API reference

Entity types
Entity	The fundamental identifier in ECS
EntityArchetype	A unique combination of component types
EntityQuery	Use to select entities with specific characteristics
EntityQueryDesc	Use to create EntityQuery objects
EntityManager	Manages entities and provides utility methods
World	An isolated collection of entities

Component types
IComponentData	A marker interface for general purpose components
ISharedComponentData	A marker interface for components shared by many entities
ISystemStateComponentData	A marker interface for specialized system components
IBufferElementData	A marker interface for buffer elements
DynamicBuffer	The API to access buffer elements
[BlobAssetReference]	A reference to a blob asset in a component

System types
ComponentSystemBase	Defines a set of basic functionality for systems
SystemBase	The base class to extend when writing an ECS system
GameObjectConversionSystem	The base class to extend when writing GameObject conversion systems
ComponentSystemGroup	A group of systems that update as a unit

ECS job types
Entities.ForEach	An implicitly created job that iterates over a set of entities. Write quick, schedule once.
Job.WithCode	An implicitly created single job
IJobEntity	An interface to implicitly create a job that iterates over the entities. Write once, schedule multiple.
IJobEntityBatch	An interface to implement to explicitly create a job that iterates over the entities returned by an entity query in batches

Other important types
ArchetypeChunk	The storage unit for entity components
EntityCommandBuffer	A buffer for recording entity modifications used to reduce structural changes
ComponentType	Use to define types when creating entity queries
BlobBuilder	A utility class for creating 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

Attributes
UpdateInGroup	Defines the ComponentSystemGroup to which a system should be added
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
GenerateAuthoringComponent	Generates a MonoBehaviour-based Component for an ECS IComponentData struct, allowing you to add it directly to a GameObject in the Unity Editor
ConverterVersion	Use to ensure that serialized data is up to date with conversion code