# 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.qi4j.api.dataset;

    import org.qi4j.api.property.Property;
    import org.qi4j.api.query.QueryException;
    import org.qi4j.api.query.QueryExecutionException;
    import org.qi4j.functional.Specification;
    import org.qi4j.functional.Visitor;

    /**
     * TODO
     */
    public interface Query<T>
    {
        public enum Order
        {
            ASCENDING, DESCENDING
        }

        Query filter( Specification<T> filter );

        Query orderBy( final Property<?> property, final Order order );

        Query skip( int skipNrOfResults );

        Query limit( int maxNrOfResults );

        // Variables
        Query<T> setVariable( String name, Object value );

        Object getVariable( String name );

        long count()
            throws QueryExecutionException;

        T first()
            throws QueryExecutionException;

        T single()
            throws QueryException;

        <ThrowableType extends Throwable> boolean execute( Visitor<T, ThrowableType> resultVisitor )
            throws ThrowableType, QueryExecutionException;

        Iterable<T> toIterable()
            throws QueryExecutionException;
    }