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experiment with a SimpleProjectionSpecification
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‎hibernate-core/src/main/java/org/hibernate/query/specification/SimpleProjectionSpecification.java‎

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/*
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* SPDX-License-Identifier: Apache-2.0
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* Copyright Red Hat Inc. and Hibernate Authors
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*/
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package org.hibernate.query.specification;
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import jakarta.persistence.EntityManager;
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import jakarta.persistence.TypedQueryReference;
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import jakarta.persistence.criteria.CriteriaBuilder;
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import jakarta.persistence.criteria.CriteriaQuery;
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import jakarta.persistence.metamodel.SingularAttribute;
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import org.hibernate.Incubating;
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import org.hibernate.Session;
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import org.hibernate.StatelessSession;
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import org.hibernate.query.SelectionQuery;
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import org.hibernate.query.restriction.Path;
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import org.hibernate.query.specification.internal.SimpleProjectionSpecificationImpl;
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/**
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* Allows a {@link SelectionSpecification} to be augmented with the specification of
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* a single projected {@linkplain SingularAttribute attribute} or {@linkplain Path path}.
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* <pre>
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* var specification =
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* SelectionSpecification.create(Book.class)
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* .restrict(Restriction.contains(Book_.title, "hibernate", false))
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* .sort(Order.desc(Book_.title));
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* var projection = SimpleProjectionSpecification.create(specification, Book_.isbn);
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* var isbns = projection.createQuery(session).getResultList();
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* </pre>
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* <p>
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* Use of a {@link Path} allows joining to associated entities.
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* <pre>
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* var specification =
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* SelectionSpecification.create(Book.class)
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* .restrict(Restriction.contains(Book_.title, "hibernate", false))
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* .sort(Order.desc(Book_.title));
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* var projection =
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* SimpleProjectionSpecification.create(specification,
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* Path.from(Book.class)
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* .to(Book_.publisher)
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* .to(Publisher_.name));
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* var publisherNames = projection.createQuery(session).getResultList();
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* </pre>
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*
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* @param <T> The result type of the {@link SelectionSpecification}
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* @param <X> The type of the projected path or attribute
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*
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* @since 7.2
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*
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* @author Gavin King
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*/
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@Incubating
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public interface SimpleProjectionSpecification<T,X> extends QuerySpecification<T> {
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/**
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* Create a new {@code ProjectionSpecification} which augments the given
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* {@link SelectionSpecification}.
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*/
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static <T,X> SimpleProjectionSpecification<T,X> create(
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SelectionSpecification<T> selectionSpecification,
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Path<T,X> projectedPath) {
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return new SimpleProjectionSpecificationImpl<>( selectionSpecification, projectedPath );
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}
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/**
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* Create a new {@code ProjectionSpecification} which augments the given
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* {@link SelectionSpecification}.
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*/
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static <T,X> SimpleProjectionSpecification<T,X> create(
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SelectionSpecification<T> selectionSpecification,
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SingularAttribute<T,X> projectedAttribute) {
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return new SimpleProjectionSpecificationImpl<>( selectionSpecification, projectedAttribute );
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}
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@Override
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SelectionQuery<X> createQuery(Session session);
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@Override
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SelectionQuery<X> createQuery(StatelessSession session);
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@Override
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SelectionQuery<X> createQuery(EntityManager entityManager);
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@Override
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CriteriaQuery<X> buildCriteria(CriteriaBuilder builder);
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@Override
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TypedQueryReference<X> reference();
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@Override
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SimpleProjectionSpecification<T,X> validate(CriteriaBuilder builder);
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}

‎hibernate-core/src/main/java/org/hibernate/query/specification/internal/ProjectionSpecificationImpl.java‎

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}
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@Override
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public Class<? extends Object[]> getResultType() {
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public Class<Object[]> getResultType() {
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return Object[].class;
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}
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‎hibernate-core/src/main/java/org/hibernate/query/specification/internal/SimpleProjectionSpecificationImpl.java‎

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/*
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* SPDX-License-Identifier: Apache-2.0
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* Copyright Red Hat Inc. and Hibernate Authors
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*/
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package org.hibernate.query.specification.internal;
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import jakarta.persistence.EntityManager;
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import jakarta.persistence.TypedQueryReference;
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import jakarta.persistence.criteria.CriteriaBuilder;
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import jakarta.persistence.criteria.CriteriaQuery;
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import jakarta.persistence.metamodel.SingularAttribute;
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import org.hibernate.Session;
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import org.hibernate.SharedSessionContract;
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import org.hibernate.StatelessSession;
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import org.hibernate.query.SelectionQuery;
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import org.hibernate.query.restriction.Path;
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import org.hibernate.query.restriction.Restriction;
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import org.hibernate.query.specification.QuerySpecification;
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import org.hibernate.query.specification.SelectionSpecification;
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import org.hibernate.query.specification.SimpleProjectionSpecification;
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import org.hibernate.query.sqm.tree.select.SqmSelectStatement;
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import java.util.Collections;
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import java.util.Map;
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/**
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* @author Gavin King
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*/
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public class SimpleProjectionSpecificationImpl<T,X> implements SimpleProjectionSpecification<T,X>, TypedQueryReference<X> {
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private final SelectionSpecification<T> selectionSpecification;
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private final Path<T, X> path;
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private final SingularAttribute<T, X> attribute;
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public SimpleProjectionSpecificationImpl(SelectionSpecification<T> specification, Path<T, X> path) {
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this.selectionSpecification = specification;
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this.path = path;
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this.attribute = null;
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}
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public SimpleProjectionSpecificationImpl(SelectionSpecification<T> specification, SingularAttribute<T, X> attribute) {
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this.selectionSpecification = specification;
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this.attribute = attribute;
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this.path = null;
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}
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@Override
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public QuerySpecification<T> restrict(Restriction<? super T> restriction) {
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throw new UnsupportedOperationException( "This is not supported yet!" );
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}
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@Override
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public SelectionQuery<X> createQuery(Session session) {
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return session.createSelectionQuery( buildCriteria( session.getCriteriaBuilder() ) );
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}
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@Override
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public SelectionQuery<X> createQuery(StatelessSession session) {
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return session.createSelectionQuery( buildCriteria( session.getCriteriaBuilder() ) );
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}
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@Override
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public SelectionQuery<X> createQuery(EntityManager entityManager) {
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return entityManager.unwrap( SharedSessionContract.class )
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.createQuery( buildCriteria( entityManager.getCriteriaBuilder() ) );
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}
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@Override
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public CriteriaQuery<X> buildCriteria(CriteriaBuilder builder) {
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var impl = (SelectionSpecificationImpl<T>) selectionSpecification;
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// TODO: handle HQL, existing criteria
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final var tupleQuery =
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(SqmSelectStatement<X>)
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builder.createQuery( getResultType() );
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final var root = tupleQuery.from( impl.getResultType() );
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// This cast is completely bogus
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final var castStatement = (SqmSelectStatement<T>) tupleQuery;
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impl.getSpecifications().forEach( spec -> spec.accept( castStatement, root ) );
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if ( path != null ) {
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tupleQuery.select( path.path( root ) );
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}
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else if ( attribute != null ) {
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tupleQuery.select( root.get( attribute ) );
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}
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return tupleQuery;
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}
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@Override
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public SimpleProjectionSpecification<T,X> validate(CriteriaBuilder builder) {
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selectionSpecification.validate( builder );
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// TODO: validate projection
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return this;
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}
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@Override
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public TypedQueryReference<X> reference() {
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return this;
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}
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@Override
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public String getName() {
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return null;
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}
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@Override
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public Class<X> getResultType() {
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if ( path != null ) {
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return path.getType();
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}
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else if ( attribute != null ) {
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return attribute.getJavaType();
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}
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else {
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throw new IllegalStateException( "No path or attribute" );
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}
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}
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@Override
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public Map<String, Object> getHints() {
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return Collections.emptyMap();
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}
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}

‎hibernate-core/src/test/java/org/hibernate/orm/test/query/dynamic/ProjectionSpecificationTest.java‎

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import org.hibernate.query.restriction.Path;
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import org.hibernate.query.specification.ProjectionSpecification;
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import org.hibernate.query.specification.SelectionSpecification;
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import org.hibernate.query.specification.SimpleProjectionSpecification;
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import org.hibernate.testing.orm.junit.DomainModel;
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import org.hibernate.testing.orm.junit.SessionFactoryScope;
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import org.junit.jupiter.api.BeforeAll;
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assertNull( otherId.in( tuple ) );
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});
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}
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@Test
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void testSimpleProjection(SessionFactoryScope factoryScope) {
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factoryScope.inTransaction( (session) -> {
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var spec = SelectionSpecification.create( BasicEntity.class );
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var projection = SimpleProjectionSpecification.create( spec, BasicEntity_.name );
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var name = projection.createQuery( session ).getSingleResult();
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assertEquals( "Gavin", name );
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});
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}
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@Test
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void testSimpleProjectionPath(SessionFactoryScope factoryScope) {
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factoryScope.inTransaction( (session) -> {
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var spec = SelectionSpecification.create( BasicEntity.class );
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var projection = SimpleProjectionSpecification.create( spec,
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Path.from( BasicEntity.class)
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.to( BasicEntity_.other )
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.to( OtherEntity_.id ) );
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var id = projection.createQuery( session ).getSingleResult();
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assertNull( id );
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});
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}
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}

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