add convenience createProjection() methods

Author: gavinking

hibernate-core/src/main/java/org/hibernate/query/specification/SelectionSpecification.java

@@ -4,11 +4,12 @@
  */
 package org.hibernate.query.specification;
 
-import jakarta.persistence.TypedQueryReference;
 import jakarta.persistence.EntityManager;
-import jakarta.persistence.criteria.CriteriaQuery;
+import jakarta.persistence.TypedQueryReference;
 import jakarta.persistence.criteria.CriteriaBuilder;
+import jakarta.persistence.criteria.CriteriaQuery;
 import jakarta.persistence.criteria.Root;
+import jakarta.persistence.metamodel.SingularAttribute;
 
 import org.hibernate.Incubating;
 import org.hibernate.Session;
@@ -17,9 +18,9 @@
 import org.hibernate.query.Order;
 import org.hibernate.query.Page;
 import org.hibernate.query.SelectionQuery;
-import org.hibernate.query.specification.internal.SelectionSpecificationImpl;
 import org.hibernate.query.restriction.Path;
 import org.hibernate.query.restriction.Restriction;
+import org.hibernate.query.specification.internal.SelectionSpecificationImpl;
 
 import java.util.List;
 
@@ -242,4 +243,50 @@ static <T> SelectionSpecification<T> create(Class<T> resultType, String hql) {
 	static <T> SelectionSpecification<T> create(CriteriaQuery<T> criteria) {
 		return new SelectionSpecificationImpl<>( criteria );
 	}
+
+	/**
+	 * Create a {@link ProjectionSpecification} allowing selection of specific
+	 * {@linkplain ProjectionSpecification#select(SingularAttribute) fields}
+	 * and {@linkplain ProjectionSpecification#select(Path) compound paths}.
+	 * The returned projection holds a reference to this specification,
+	 * and so mutation of this object also affects the projection.
+	 *
+	 * @return a new {@link ProjectionSpecification}
+	 *
+	 * @since 7.2
+	 */
+	@Incubating
+	default ProjectionSpecification<T> createProjection() {
+		return ProjectionSpecification.create( this );
+	}
+
+	/**
+	 * Create a {@link SimpleProjectionSpecification} for the given
+	 * {@linkplain ProjectionSpecification#select(SingularAttribute) field}.
+	 * The returned projection holds a reference to this specification,
+	 * and so mutation of this object also affects the projection.
+	 *
+	 * @return a new {@link SimpleProjectionSpecification}
+	 *
+	 * @since 7.2
+	 */
+	@Incubating
+	default <X> SimpleProjectionSpecification<T,X> createProjection(SingularAttribute<? super T, X> attribute) {
+		return SimpleProjectionSpecification.create( this, attribute );
+	}
+
+	/**
+	 * Create a {@link SimpleProjectionSpecification} for the given
+	 * {@linkplain ProjectionSpecification#select(Path) compound path}.
+	 * The returned projection holds a reference to this specification,
+	 * and so mutation of this object also affects the projection.
+	 *
+	 * @return a new {@link SimpleProjectionSpecification}
+	 *
+	 * @since 7.2
+	 */
+	@Incubating
+	default <X> SimpleProjectionSpecification<T,X> createProjection(Path<T, X> path) {
+		return SimpleProjectionSpecification.create( this, path );
+	}
 }

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

@@ -5,9 +5,7 @@
 package org.hibernate.orm.test.query.dynamic;
 
 import org.hibernate.query.restriction.Path;
-import org.hibernate.query.specification.ProjectionSpecification;
 import org.hibernate.query.specification.SelectionSpecification;
-import org.hibernate.query.specification.SimpleProjectionSpecification;
 import org.hibernate.testing.orm.junit.DomainModel;
 import org.hibernate.testing.orm.junit.SessionFactoryScope;
 import org.junit.jupiter.api.BeforeAll;
@@ -36,7 +34,7 @@ public static void setup(SessionFactoryScope factoryScope) {
 	void testProjection(SessionFactoryScope factoryScope) {
 		factoryScope.inTransaction( (session) -> {
 			var spec = SelectionSpecification.create( BasicEntity.class );
-			var projection = ProjectionSpecification.create( spec );
+			var projection = spec.createProjection();
 			var position = projection.select( BasicEntity_.position );
 			var name = projection.select( BasicEntity_.name );
 			var id = projection.select( Path.from( BasicEntity.class ).to( BasicEntity_.id ) );
@@ -53,7 +51,7 @@ void testProjection(SessionFactoryScope factoryScope) {
 	void testSimpleProjection(SessionFactoryScope factoryScope) {
 		factoryScope.inTransaction( (session) -> {
 			var spec = SelectionSpecification.create( BasicEntity.class );
-			var projection = SimpleProjectionSpecification.create( spec, BasicEntity_.name );
+			var projection = spec.createProjection( BasicEntity_.name );
 			var name = projection.createQuery( session ).getSingleResult();
 			assertEquals( "Gavin", name );
 		});
@@ -63,10 +61,11 @@ void testSimpleProjection(SessionFactoryScope factoryScope) {
 	void testSimpleProjectionPath(SessionFactoryScope factoryScope) {
 		factoryScope.inTransaction( (session) -> {
 			var spec = SelectionSpecification.create( BasicEntity.class );
-			var projection = SimpleProjectionSpecification.create( spec,
-					Path.from( BasicEntity.class)
-							.to( BasicEntity_.other )
-							.to( OtherEntity_.id ) );
+			var projection =
+					spec.createProjection(
+							Path.from( BasicEntity.class)
+									.to( BasicEntity_.other )
+									.to( OtherEntity_.id ) );
 			var id = projection.createQuery( session ).getSingleResult();
 			assertNull( id );
 		});