org.apache.cayenne.query

Interface Select<T>

All Superinterfaces:

Query, Serializable

All Known Implementing Classes:

ColumnSelect, FluentSelect, MappedSelect, ObjectSelect, PrefetchSelectQuery, SelectById, SelectQuery, SQLSelect

public interface Select<T>
extends Query

A common interface for grouping together different kinds of queries that return results.

Method Summary

Modifier and Type	Method and Description
ResultBatchIterator<T>	batchIterator(ObjectContext context, int size) Creates a ResultBatchIterator based on the provided context and batch size.
void	iterate(ObjectContext context, ResultIteratorCallback<T> callback) Creates a ResultIterator based on the provided context and passes it to a callback for processing.
ResultIterator<T>	iterator(ObjectContext context) Creates a ResultIterator based on the provided context.
List<T>	select(ObjectContext context) Selects objects using provided context.
T	selectFirst(ObjectContext context) Selects a single object using provided context.
T	selectOne(ObjectContext context) Selects a single object using provided context.

Methods inherited from interface org.apache.cayenne.query.Query

createSQLAction, getDataMap, getMetaData, getName, route

Method Detail

select

List<T> select(ObjectContext context)

Selects objects using provided context.

Essentially the inversion of "ObjectContext.select(Select)".

Since:

4.0

selectOne

T selectOne(ObjectContext context)

Selects a single object using provided context. The query is expected to match zero or one object. It returns null if no objects were matched. If query matched more than one object, CayenneRuntimeException is thrown.

Essentially the inversion of "ObjectContext.selectOne(Select)".

Since:

4.0

selectFirst

T selectFirst(ObjectContext context)

Selects a single object using provided context. The query itself can match any number of objects, but will return only the first one. It returns null if no objects were matched.

If it matched more than one object, the first object from the list is returned. This makes 'selectFirst' different from selectOne(ObjectContext), which would throw in this situation. 'selectFirst' is useful e.g. when the query is ordered and we only want to see the first object (e.g. "most recent news article"), etc.

Selecting the first object via "Select.selectFirst(ObjectContext)" is more comprehensible than selecting via "ObjectContext.selectFirst(Select)", because implementations of "Select" set fetch size limit to one.

Since:

4.0

iterate

void iterate(ObjectContext context,
             ResultIteratorCallback<T> callback)

Creates a ResultIterator based on the provided context and passes it to a callback for processing. The caller does not need to worry about closing the iterator. This method takes care of it.

Essentially the inversion of "ObjectContext.iterate(Select, ResultIteratorCallback)".

Since:

4.0

iterator

ResultIterator<T> iterator(ObjectContext context)

Creates a ResultIterator based on the provided context. It is usually backed by an open result set and is useful for processing of large data sets, preserving a constant memory footprint. The caller must wrap iteration in try/finally (or try-with-resources for Java 1.7 and higher) and close the ResultIterator explicitly. Or use iterate(ObjectContext, ResultIteratorCallback) as an alternative.

Essentially the inversion of "ObjectContext.iterator(Select)".

Since:

4.0

batchIterator

ResultBatchIterator<T> batchIterator(ObjectContext context,
                                     int size)

Creates a ResultBatchIterator based on the provided context and batch size. It is usually backed by an open result set and is useful for processing of large data sets, preserving a constant memory footprint. The caller must wrap iteration in try/finally (or try-with-resources for Java 1.7 and higher) and close the ResultBatchIterator explicitly.

Since:

4.0