org.lenskit.data.dao

Interface Query<E extends Entity>

public interface Query<E extends Entity>

Fluent interface for DAO queries. This interface is immutable - new objects are always returned - so it is safe to save partial queries and use them to build up more sophisticated queries.

An implementation on top of the base DAO methods is used by AbstractDataAccessObject. Other DAO implementations can reimplement this interface in other ways, for example to generate SQL queries.

Method Summary

Modifier and Type	Method and Description
<V extends Entity> Query<V>	asType(Class<V> type) View results as a different type.
int	count() Get the number of results the query would return.
List<E>	get() Get the results of this query as a list.
GroupedQuery<E>	groupBy(String name) Group the results of this query by an attribute.
GroupedQuery<E>	groupBy(TypedName<Long> name) Group the results of this query by an attribute.
Query<E>	orderBy(TypedName<? extends Comparable<?>> name) Sort the query results by a field.
Query<E>	orderBy(TypedName<? extends Comparable<?>> name, SortOrder order) Sort the query results by a field.
ObjectStream<E>	stream() Stream the results of this query.
LongSet	valueSet(TypedName<Long> attr) Get the set of values from an attribute in the entities in this query.
<T> Query<E>	withAttribute(TypedName<T> name, T value) Add an attribute value condition to the query.

Method Detail

withAttribute

<T> Query<E> withAttribute(TypedName<T> name,
                           T value)

Add an attribute value condition to the query.

Parameters:

name - The attribute name.

value - The attribute value.

T - The attribute type.

Returns:

A query.

orderBy

Query<E> orderBy(TypedName<? extends Comparable<?>> name)

Sort the query results by a field.

Parameters:

name - The field name.

Returns:

A query.

orderBy

Query<E> orderBy(TypedName<? extends Comparable<?>> name,
                 SortOrder order)

Sort the query results by a field.

Parameters:

name - The field name.

order - The sort order.

Returns:

A query.

asType

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

View results as a different type.

Parameters:

type - The entity view type.

V - The entity view type.

Returns:

A query.

groupBy

GroupedQuery<E> groupBy(TypedName<Long> name)

Group the results of this query by an attribute.

Parameters:

name - The attribute name to group by.

Returns:

A grouped query.

groupBy

GroupedQuery<E> groupBy(String name)

Group the results of this query by an attribute.

Parameters:

name - The attribute name to group by.

Returns:

A grouped query.

stream

ObjectStream<E> stream()

Stream the results of this query.

Returns:

A stream of the results of this query.

get

List<E> get()

Get the results of this query as a list.

Returns:

A list of the results of this query.

count

int count()

Get the number of results the query would return.

Returns:

The number of entities returned by the query.

valueSet

LongSet valueSet(TypedName<Long> attr)

Get the set of values from an attribute in the entities in this query. Use this to do things like get the set of items referenced in a user’s ratings:

dao.query(Rating.class)
   .withAttribute(CommonAttributes.USER_ID, user)
   .valueSet(CommonAttributes.ITEM_ID);

Parameters:

attr - The attribute name to select.

Returns:

The set of values attribute takes on in the query.