# OrderBy.java

    /*
     * Copyright 2007 Niclas Hedhman.
     * Copyright 2008 Alin Dreghiciu.
     *
     * Licensed  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.query.grammar;

    /**
     * Query sorting segment.
     */
    public class OrderBy
    {
        /**
         * Order direction.
         */
        public enum Order
        {
            ASCENDING, DESCENDING
        }

        /**
         * Order.
         */
        private final PropertyFunction<?> propertyReference;
        /**
         * Direction.
         */
        private final Order order;

        /**
         * Constructor.
         *
         * @param propertyReference property that determines the order; cannot be null
         * @param order             direction
         *
         * @throws IllegalArgumentException - If property is null
         */
        public OrderBy( final PropertyFunction<?> propertyReference,
                        final Order order
        )
        {
            if( propertyReference == null )
            {
                throw new IllegalArgumentException( "Ordering property cannot be null" );
            }
            this.propertyReference = propertyReference;
            this.order = order;
        }

        /**
         * Getter.
         *
         * @return property; cannot be null
         */
        public PropertyFunction<?> property()
        {
            return propertyReference;
        }

        /**
         * Getter.
         *
         * @return direction; cannot be null
         */
        public Order order()
        {
            return order;
        }

        @Override
        public String toString()
        {
            return new StringBuilder()
                .append( propertyReference )
                .append( " " )
                .append( order )
                .toString();
        }
    }