Query.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing,
 *  software distributed under the License is distributed on an
 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *  KIND, either express or implied.  See the License for the
 *  specific language governing permissions and limitations
 *  under the License.
 */

package org.apache.isis.applib.query;

import java.io.Serializable;

import com.google.common.base.Predicate;

import org.apache.isis.applib.DomainObjectContainer;

/**
 * For use by repository implementations, representing the values of a query.
 * 
 * <p>
 * The implementations of these objects are be provided by the underlying
 * persistor/object store; consult its documentation.
 * <p>
 * Implementations are expected to implement the {@link #getStart()} and 
 * {@link #getCount()} methods, which are used to support range / paging
 * the data. Returned result sets are expected to start from index "start",
 * and no more than "count" items are expected. 
 * <p>
 * <b>Note:</b> that not every object store will necessarily support this
 * interface. In particular, the in-memory object store does not. For this, you
 * can use the {@link Predicate} interface to similar effect, for example in
 * {@link DomainObjectContainer#allMatches(Class, Predicate, long...)}). Note that the
 * predicate is applied within the {@link DomainObjectContainer} (ie client-side)
 * rather than being pushed back to the object store.
 */
public interface Query<T> extends Serializable {

    /**
     * The {@link Class} of the objects returned by this query.
     */
    public Class<T> getResultType();

    /**
     * A human-readable representation of this query and its values.
     */
    public String getDescription();

    /**
     * The start index into the set table
     * @return
     */
    public long getStart();


    /**
     * The number of items to return, starting at {@link #getStart()}
     * @return
     */
    public long getCount();
}