oracle.toplink.essentials.queryframework.ValueReadQuery Maven / Gradle / Ivy
/*
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* of the Common Development and Distribution License
* (the "License"). You may not use this file except
* in compliance with the License.
*
* You can obtain a copy of the license at
* glassfish/bootstrap/legal/CDDLv1.0.txt or
* https://glassfish.dev.java.net/public/CDDLv1.0.html.
* See the License for the specific language governing
* permissions and limitations under the License.
*
* When distributing Covered Code, include this CDDL
* HEADER in each file and include the License file at
* glassfish/bootstrap/legal/CDDLv1.0.txt. If applicable,
* add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your
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// Copyright (c) 1998, 2007, Oracle. All rights reserved.
package oracle.toplink.essentials.queryframework;
import oracle.toplink.essentials.internal.queryframework.*;
import oracle.toplink.essentials.exceptions.*;
/**
* Purpose:
* Concrete class to perform a read of a single data value.
*
*
Responsibilities:
* Used in conjunction with CursoredStream size and Platform getSequence.
* This can be used to read a single data value (i.e. one field).
* A single data value is returned, or null if no rows are returned.
*
* @author James Sutherland
* @since TOPLink/Java 1.2
*/
public class ValueReadQuery extends DirectReadQuery {
/**
* PUBLIC:
* Initialize the state of the query.
*/
public ValueReadQuery() {
super();
}
/**
* PUBLIC:
* Initialize the query to use the specified SQL string.
*/
public ValueReadQuery(String sqlString) {
super(sqlString);
}
/**
* PUBLIC:
* Initialize the query to use the specified call.
*/
public ValueReadQuery(Call call) {
super(call);
}
/**
* INTERNAL:
* Execute the query.
* Perform the work to execute the SQL string.
* @exception DatabaseException an error has occurred on the database
* @return Object the data value or null.
*/
public Object executeDatabaseQuery() throws DatabaseException {
Object values = super.executeDatabaseQuery();
ContainerPolicy cp = getContainerPolicy();
if (cp.sizeFor(values) == 0) {
return null;
} else {
return cp.next(cp.iteratorFor(values), getSession());
}
}
}