foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/internal/jpa/jpql/DerivedDeclaration.java

/*
 * Copyright (c) 2011, 2021 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Oracle - initial API and implementation
//
package org.eclipse.persistence.internal.jpa.jpql;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.expressions.Expression;
import org.eclipse.persistence.expressions.ExpressionBuilder;
import org.eclipse.persistence.mappings.DatabaseMapping;

/**
 * This <code>DerivedDeclaration</code> represents an identification variable declaration that was
 * declared in the <code><b>FROM</b></code> clause of a <code><b>SELECT</b></code> subquery. The
 * "root" object is not an entity name but a derived path expression.
 *
 * @see org.eclipse.persistence.jpa.jpql.parser.IdentificationVariableDeclaration IdentificationVariableDeclaration
 *
 * @version 2.5
 * @since 2.4
 * @author Pascal Filion
 */
final class DerivedDeclaration extends AbstractRangeDeclaration {

    /**
     * Creates a new <code>DerivedDeclaration</code>.
     *
     * @param queryContext The context used to query information about the application metadata and
     * cached information
     */
    DerivedDeclaration(JPQLQueryContext queryContext) {
        super(queryContext);
    }

    @Override
    Expression buildQueryExpression() {

        DatabaseMapping mapping = resolveMapping();

        // If the derived expression is a class (non direct collection), then create a new expression
        // builder for it, this builder will be compared as equal to the outer reference
        if ((mapping != null) && (mapping.getReferenceDescriptor() != null)) {

            Expression expression = new ExpressionBuilder(mapping.getReferenceDescriptor().getJavaClass());
            queryContext.addUsedIdentificationVariable(rootPath);
            queryContext.addQueryExpression(rootPath, expression);

            // Check to see if the Expression exists in the parent's context,
            // if not, then create/cache a new instance
            JPQLQueryContext parentContext = queryContext.getParent();

            if (parentContext.getQueryExpressionImp(rootPath) == null) {
                parentContext.addQueryExpressionImp(rootPath, queryContext.buildExpression(baseExpression));
            }

            return expression;
        }
        else {

            // Otherwise it will be derived by duplicating the join to the outer builder inside the
            // sub select. The same could be done for direct collection, but difficult to create a
            // builder on a table. Retrieve the superquery identification variable from the derived path
            int index = rootPath.indexOf('.');
            String superqueryVariableName = rootPath.substring(0, index).toUpperCase().intern();

            // Create the local ExpressionBuilder for the super identification variable
            Expression expression = queryContext.getParent().findQueryExpressionImp(superqueryVariableName);

            expression = new ExpressionBuilder(expression.getBuilder().getQueryClass());
            queryContext.addUsedIdentificationVariable(superqueryVariableName);
            queryContext.addQueryExpression(superqueryVariableName, expression);

            // Now create the base Expression for the actual derived path
            return queryContext.buildExpression(baseExpression);
        }
    }

    @Override
    public Type getType() {
        return Type.DERIVED;
    }

    @Override
    ClassDescriptor resolveDescriptor() {
        return queryContext.resolveDescriptor(getBaseExpression().getRootObject());
    }

    @Override
    DatabaseMapping resolveMapping() {
        return queryContext.resolveMapping(getBaseExpression().getRootObject());
    }
}