    001// Copyright 2007, 2008 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007//     http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5.grid;
    016
    017import java.util.List;
    018
    019/**
    020 * Defines how a {@link org.apache.tapestry5.corelib.components.Grid} component (and its sub-components) gain access to
    021 * the row data that is displayed on the page. In many cases, this is just a wrapper around a simple List, but the
    022 * abstractions exist to support access to a large data set that is accessible in sections.
    023 */
    024public interface GridDataSource
    025{
    026
    027    /**
    028     * Return whether the data source is empty, i.e. does not have any rows available.
    029     */
    030    default public boolean isEmpty()
    031    {
    032        return getAvailableRows(1) == 0;
    033    }
    034
    035    /**
    036     * Return the number of rows available in the data source with an upper limit.
    037     * If determining the total number of rows is expensive, this method should be overridden to provide a more
    038     * efficient implementation.
    039     * Please note that the default Grid pager will still determine the total number of rows, so for this to have
    040     * an effect, a custom pager should be used.
    041     *
    042     * @param limit the upper limit
    043     * @return the number of rows or {@code limit}, whichever is lower
    044     */
    045    default public int getAvailableRows(final int limit)
    046    {
    047        int availableRows = getAvailableRows();
    048        if (availableRows >= limit)
    049        {
    050            return limit;
    051        }
    052        return availableRows;
    053    }
    054
    055    /**
    056     * Returns the number of rows available in the data source.
    057     */
    058    int getAvailableRows();
    059
    060    /**
    061     * Invoked to allow the source to prepare to present values. This gives the source a chance to pre-fetch data (when
    062     * appropriate) and informs the source of the desired sort order.  Sorting comes first, then extraction by range.
    063     *
    064     * @param startIndex      the starting index to be retrieved
    065     * @param endIndex        the ending index to be retrieved
    066     * @param sortConstraints identify how data is to be sorted
    067     */
    068    void prepare(int startIndex, int endIndex, List<SortConstraint> sortConstraints);
    069
    070    /**
    071     * Returns the row value at the provided index. This method will be invoked in sequential order. In rare instances,
    072     * {@link #getAvailableRows()} may return a different number of rows than are actually available (i.e., the database
    073     * was changed between calls to {@link #getAvailableRows()} and the call to {@link #prepare(int, int,
    074     * java.util.List)}).  In that case, this method should return null for any out-of-range indexes.
    075     */
    076    Object getRowValue(int index);
    077
    078    /**
    079     * Returns the type of value in the rows, or null if not known. This value is used to create a default {@link
    080     * org.apache.tapestry5.beanmodel.BeanModel} when no such model is explicitly provided.
    081     *
    082     * @return the row type, or null
    083     */
    084    Class getRowType();
    085}