HHH-18517 allow composition of CriteriaDefinitions

Signed-off-by: Gavin King <gavin@hibernate.org>

hibernate-core/src/main/java/org/hibernate/query/criteria/CriteriaDefinition.java

@@ -18,6 +18,8 @@ import org.hibernate.query.QueryProducer;
 import org.hibernate.query.SelectionQuery;
 import org.hibernate.query.criteria.spi.HibernateCriteriaBuilderDelegate;
 import org.hibernate.query.sqm.FetchClauseType;
+import org.hibernate.query.sqm.tree.SqmCopyContext;
+import org.hibernate.query.sqm.tree.select.SqmSelectStatement;
 
 import java.util.Collection;
 import java.util.List;
@@ -85,6 +87,28 @@ import java.util.function.Function;
  *     ...
  * });
  * </pre>
+ * A {@code CriteriaDefinition} may be used to modify another {@code CriteriaDefinition}:
+ * <pre>
+ * var bookFilter
+ *         = new CriteriaDefinition&lt;&gt;(sessionFactory, Book.class) {{
+ *             where(like(from(Book.class).get(Book_.title), "%Hibernate%"));
+ *         }};
+ * long count
+ *         = new CriteriaDefinition&lt;&gt;(bookFilter, Long.class) {{
+ *             select(count());
+ *         }}
+ *         .createSelectionQuery(session)
+ *         .getSingleResult();
+ * var books =
+ *         = new CriteriaDefinition&lt;&gt;(bookFilter) {{
+ *             var book = (Root&lt;Book&gt;) getRootList().get(0);
+ *             book.fetch(Book_.authors);
+ *             orderBy(desc(book.get(Book_.publicationDate)), asc(book.get(Book_.isbn)));
+ *         }}
+ *         .createSelectionQuery(session)
+ *         .setMaxResults(10)
+ *         .getResultList();
+ * </pre>
  *
  * @param <R> the query result type
  *
@@ -99,6 +123,37 @@ public abstract class CriteriaDefinition<R>
 
 	private final JpaCriteriaQuery<R> query;
 
+	/**
+	 * Construct a new {@code CriteriaDefinition} based on the given
+	 * {@code CriteriaDefinition}, with the same query return type.
+	 *
+	 * @param template the original query
+	 *
+	 * @since 7.0
+	 */
+	public CriteriaDefinition(CriteriaDefinition<R> template) {
+		super( template.getCriteriaBuilder() );
+		query = ((SqmSelectStatement<R>) template.query)
+				.copy( SqmCopyContext.simpleContext() );
+	}
+
+	/**
+	 * Construct a new {@code CriteriaDefinition} based on the given
+	 * {@code CriteriaDefinition}. This overload permits changing the
+	 * query return type. It is expected that {@link #select} be called
+	 * to rewrite the selection list.
+	 *
+	 * @param template the original query
+	 * @param resultType the new return type
+	 *
+	 * @since 7.0
+	 */
+	public CriteriaDefinition(CriteriaDefinition<?> template, Class<R> resultType) {
+		super( template.getCriteriaBuilder() );
+		query = ((SqmSelectStatement<?>) template.query)
+				.createCopy( SqmCopyContext.simpleContext(), resultType );
+	}
+
 	public CriteriaDefinition(SessionFactory factory, Class<R> resultType) {
 		super( factory.getCriteriaBuilder() );
 		query = createQuery( resultType );

hibernate-core/src/main/java/org/hibernate/query/sqm/tree/select/SqmSelectStatement.java

@@ -13,6 +13,7 @@ import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
 
+import org.hibernate.Internal;
 import org.hibernate.query.criteria.JpaCriteriaQuery;
 import org.hibernate.query.criteria.JpaExpression;
 import org.hibernate.query.criteria.JpaSelection;
@@ -26,8 +27,6 @@ import org.hibernate.query.sqm.tree.SqmStatement;
 import org.hibernate.query.sqm.tree.cte.SqmCteStatement;
 import org.hibernate.query.sqm.tree.expression.ValueBindJpaCriteriaParameter;
 import org.hibernate.query.sqm.tree.expression.SqmParameter;
-import org.hibernate.query.sqm.tree.expression.SqmStar;
-import org.hibernate.query.sqm.tree.expression.ValueBindJpaCriteriaParameter;
 import org.hibernate.query.sqm.tree.from.SqmFromClause;
 import org.hibernate.query.sqm.tree.predicate.SqmPredicate;
 import org.hibernate.query.sqm.tree.from.SqmRoot;
@@ -127,7 +126,8 @@ public class SqmSelectStatement<T> extends AbstractSqmSelectQuery<T> implements
 		return createCopy( context, getResultType() );
 	}
 
-	private <X> SqmSelectStatement<X> createCopy(SqmCopyContext context, Class<X> resultType) {
+	@Internal
+	public <X> SqmSelectStatement<X> createCopy(SqmCopyContext context, Class<X> resultType) {
 		final Set<SqmParameter<?>> parameters;
 		if ( this.parameters == null ) {
 			parameters = null;

hibernate-core/src/test/java/org/hibernate/orm/test/jpa/criteria/query/CriteriaDefinitionTest.java

@@ -54,6 +54,11 @@ public class CriteriaDefinitionTest {
             orderBy(asc(message.get("id")));
         }};
 
+        var query5 = new CriteriaDefinition<>(query4, Long.class) {{
+            select(count());
+            orderBy();
+        }};
+
         scope.inSession(session -> {
             var idAndText = session.createSelectionQuery(query1).getSingleResult();
             assertNotNull(idAndText);
@@ -72,6 +77,9 @@ public class CriteriaDefinitionTest {
             assertNotNull(msg);
             assertEquals(1L,msg.id);
             assertEquals("hello",msg.text);
+
+            long count = session.createSelectionQuery(query5).getSingleResult();
+            assertEquals(1L,count);
         });
     }