org.lenskit.data.dao

Interface DataAccessObject

All Known Implementing Classes:

AbstractDataAccessObject, EntityCollectionDAO

public interface DataAccessObject

Interface for accessing data in LensKit.

LensKit data is represented by entities; see org.lenskit.data.entities

DAOs must be thread-safe, but individual streams they return need not be.

Method Summary

Modifier and Type	Method and Description
LongSet	getEntityIds(EntityType type) Get the IDs of all entities with a particular type.
Set<EntityType>	getEntityTypes() Get the types of entities that are available in this DAO.
Entity	lookupEntity(EntityType type, long id) Look up an entity by ID.
<E extends Entity> E	lookupEntity(EntityType type, long id, Class<E> view) Look up an entity by ID and project it to a view class.
<V extends Entity> Query<V>	query(Class<V> type) Start a query for a particular type using the fluent query interface.
Query<Entity>	query(EntityType type) Start a query using the fluent query interface.
<E extends Entity> ObjectStream<E>	streamEntities(EntityQuery<E> query) Stream entities in response to a query.
ObjectStream<Entity>	streamEntities(EntityType type) Stream all entities of a particular type.
<E extends Entity> ObjectStream<IdBox<List<E>>>	streamEntityGroups(EntityQuery<E> query, TypedName<Long> grpCol) Stream entities in response to a query, grouping them by a long ID.

Method Detail

getEntityTypes

Set<EntityType> getEntityTypes()

Get the types of entities that are available in this DAO.

Returns:

The set of available entity types.

getEntityIds

LongSet getEntityIds(EntityType type)

Get the IDs of all entities with a particular type.

Parameters:

type - The entity type.

Returns:

The set of item IDs.

lookupEntity

@Nullable
Entity lookupEntity(EntityType type,
                               long id)

Look up an entity by ID.

Parameters:

type - The entity type.

id - The entity ID.

Returns:

The entity, or null if no such entity exists.

lookupEntity

@Nullable
<E extends Entity> E lookupEntity(EntityType type,
                                             long id,
                                             Class<E> view)

Look up an entity by ID and project it to a view class.

Parameters:

type - The entity type.

id - The entity ID.

view - The view class.

Returns:

The entity, or null if no such entity exists.

Throws:

IllegalArgumentException - if the entity cannot be projected to view.

streamEntities

ObjectStream<Entity> streamEntities(EntityType type)

Stream all entities of a particular type.

Parameters:

type - The entity type.

Returns:

The stream of the entities.

streamEntities

<E extends Entity> ObjectStream<E> streamEntities(EntityQuery<E> query)

Stream entities in response to a query.

Parameters:

query - The query.

E - The view class type.

Returns:

The stream of the entities.

Throws:

UnsupportedQueryException - if the query cannot be satisfied.

streamEntityGroups

<E extends Entity> ObjectStream<IdBox<List<E>>> streamEntityGroups(EntityQuery<E> query,
                                                                   TypedName<Long> grpCol)

Stream entities in response to a query, grouping them by a long ID.

Parameters:

query - The query.

grpCol - The column to group by.

E - The view class type.

Returns:

The stream of the entities.

Throws:

UnsupportedQueryException - if the query cannot be satisfied

query

Query<Entity> query(EntityType type)

Start a query using the fluent query interface.

Parameters:

type - The type of entity to retrieve.

Returns:

The query.

query

<V extends Entity> Query<V> query(Class<V> type)

Start a query for a particular type using the fluent query interface. This method looks up the entity type using the DefaultEntityType annotation on the view class.

Parameters:

type - The view class type.

Returns:

The query.

Throws:

IllegalArgumentException - if the type has no DefaultEntityType annotation.