    001// Licensed under the Apache License, Version 2.0 (the "License");
    002// you may not use this file except in compliance with the License.
    003// You may obtain a copy of the License at
    004//
    005// http://www.apache.org/licenses/LICENSE-2.0
    006//
    007// Unless required by applicable law or agreed to in writing, software
    008// distributed under the License is distributed on an "AS IS" BASIS,
    009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    010// See the License for the specific language governing permissions and
    011// limitations under the License.
    012
    013package org.apache.tapestry5.jpa;
    014
    015import org.apache.tapestry5.grid.GridDataSource;
    016import org.apache.tapestry5.grid.SortConstraint;
    017
    018import javax.persistence.EntityManager;
    019import javax.persistence.TypedQuery;
    020import javax.persistence.criteria.CriteriaBuilder;
    021import javax.persistence.criteria.CriteriaQuery;
    022import javax.persistence.criteria.Path;
    023import javax.persistence.criteria.Root;
    024import java.util.List;
    025
    026/**
    027 * A simple implementation of {@link org.apache.tapestry5.grid.GridDataSource} based on a
    028 * {@linkplain javax.persistence.EntityManager} and a known
    029 * entity class. This implementation does support multiple
    030 * {@link org.apache.tapestry5.grid.SortConstraint sort
    031 * constraints}.
    032 *
    033 * This class is <em>not</em> thread-safe; it maintains internal state.
    034 *
    035 * Typically, an instance of this object is created fresh as needed (that is, it is not stored
    036 * between requests).
    037 *
    038 * @since 5.3
    039 */
    040public class JpaGridDataSource<E> implements GridDataSource
    041{
    042
    043    private final EntityManager entityManager;
    044
    045    private final Class<E> entityType;
    046
    047    private int startIndex;
    048
    049    private List<E> preparedResults;
    050
    051    public JpaGridDataSource(final EntityManager entityManager, final Class<E> entityType)
    052    {
    053        super();
    054        this.entityManager = entityManager;
    055        this.entityType = entityType;
    056    }
    057
    058    /**
    059     * {@inheritDoc}
    060     */
    061    @Override
    062    public int getAvailableRows()
    063    {
    064        final CriteriaBuilder builder = entityManager.getCriteriaBuilder();
    065
    066        CriteriaQuery<Long> criteria = builder.createQuery(Long.class);
    067
    068        final Root<E> root = criteria.from(entityType);
    069
    070        criteria = criteria.select(builder.count(root));
    071
    072        applyAdditionalConstraints(criteria, root, builder);
    073
    074        return entityManager.createQuery(criteria).getSingleResult().intValue();
    075    }
    076
    077    /**
    078     * {@inheritDoc}
    079     */
    080    @Override
    081    public void prepare(final int startIndex, final int endIndex,
    082            final List<SortConstraint> sortConstraints)
    083    {
    084        final CriteriaBuilder builder = entityManager.getCriteriaBuilder();
    085
    086        final CriteriaQuery<E> criteria = builder.createQuery(entityType);
    087
    088        final Root<E> root = criteria.from(entityType);
    089
    090        applyAdditionalConstraints(criteria.select(root), root, builder);
    091
    092        for (final SortConstraint constraint : sortConstraints)
    093        {
    094
    095            final String propertyName = constraint.getPropertyModel().getPropertyName();
    096
    097            final Path<Object> propertyPath = root.get(propertyName);
    098
    099            switch (constraint.getColumnSort())
    100            {
    101
    102                case ASCENDING:
    103
    104                    criteria.orderBy(builder.asc(propertyPath));
    105                    break;
    106
    107                case DESCENDING:
    108                    criteria.orderBy(builder.desc(propertyPath));
    109                    break;
    110
    111                default:
    112            }
    113        }
    114
    115        final TypedQuery<E> query = entityManager.createQuery(criteria);
    116
    117        query.setFirstResult(startIndex);
    118        query.setMaxResults(endIndex - startIndex + 1);
    119
    120        this.startIndex = startIndex;
    121
    122        preparedResults = query.getResultList();
    123
    124    }
    125
    126    protected void applyAdditionalConstraints(final CriteriaQuery<?> criteria, final Root<E> root,
    127            final CriteriaBuilder builder)
    128    {
    129    }
    130
    131    /**
    132     * {@inheritDoc}
    133     */
    134    @Override
    135    public Object getRowValue(final int index)
    136    {
    137        return preparedResults.get(index - startIndex);
    138    }
    139
    140    /**
    141     * {@inheritDoc}
    142     */
    143    @Override
    144    public Class<E> getRowType()
    145    {
    146        return entityType;
    147    }
    148
    149}