/*******************************************************************************
* Copyright (c) 1998, 2013 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 v1.0 and Eclipse Distribution License v. 1.0
* which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
* and the Eclipse Distribution License is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* Contributors:
* Oracle - initial API and implementation from Oracle TopLink
******************************************************************************/
package org.eclipse.persistence.internal.expressions;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.exceptions.QueryException;
import org.eclipse.persistence.expressions.*;
import org.eclipse.persistence.internal.helper.DatabaseField;
import org.eclipse.persistence.internal.queries.ReportItem;
import org.eclipse.persistence.internal.sessions.AbstractSession;
import org.eclipse.persistence.mappings.DatabaseMapping;
import org.eclipse.persistence.mappings.querykeys.DirectQueryKey;
import org.eclipse.persistence.mappings.querykeys.QueryKey;
import org.eclipse.persistence.queries.ReportQuery;
/**
* Represents an alias to a item selected by a from clause sub-select.
*/
public class FromAliasExpression extends QueryKeyExpression {
protected ReportItem item;
protected ClassDescriptor containingDescriptor;
public FromAliasExpression() {
super();
}
public FromAliasExpression(String name, Expression base) {
super(name, base);
}
/**
* INTERNAL:
* Used for debug printing.
*/
@Override
public String descriptionOfNodeType() {
return "From Alias";
}
/**
* INTERNAL:
* If a descriptor cannot be found, then return null.
*/
@Override
public QueryKey getQueryKeyOrNull() {
if (!hasQueryKey) {
return null;
}
if (getContainingDescriptor() == null) {
// Assign an artificial query key to represent the alias.
DirectQueryKey alias = new DirectQueryKey();
alias.setField(new DatabaseField(this.name));
ReportQuery subQuery = ((FromSubSelectExpression)getBaseExpression()).getSubSelect().getSubQuery();
alias.setDescriptor(subQuery.getDescriptor());
this.queryKey = alias;
return alias;
}
return super.getQueryKeyOrNull();
}
/**
* INTERNAL:
* If the alias is for a query key item, then return its descriptor.
* If it is for a function, then it has no descriptor.
*/
@Override
public ClassDescriptor getContainingDescriptor() {
AbstractSession session = getBuilder().getSession();
if (this.containingDescriptor == null) {
Expression expression = getItem().getAttributeExpression();
if (expression.isQueryKeyExpression()) {
// Need to ensure expression has a session before getting its descriptor.
if (expression.getBuilder().getSession() == null) {
expression.getBuilder().setSession(session);
}
this.containingDescriptor = ((QueryKeyExpression)expression).getContainingDescriptor();
return this.containingDescriptor;
}
return null;
}
return containingDescriptor;
}
/**
* INTERNAL:
* Return the report item that this is an alias for.
*/
public ReportItem getItem() {
if (this.item == null) {
ReportQuery subQuery = ((FromSubSelectExpression)getBaseExpression()).getSubSelect().getSubQuery();
this.item = subQuery.getItem(this.name);
if (this.item == null) {
throw QueryException.invalidQueryKeyInExpression(this.name);
}
}
return this.item;
}
}