1 package org.apache.onami.persist;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import javax.inject.Provider;
23 import javax.persistence.EntityManager;
24
25 /**
26 * Provider for {@link EntityManager}.
27 * <p/>
28 * Even though this class extends the {@link Provider} interface it is not bound as a provider of
29 * {@link EntityManager}. The reason for this is that the {@link EntityManager} objects do have a
30 * life cycle and should therefore not be stored in instance/member variables.
31 * <p/>
32 * The {@link UnitOfWork} defines the life cycle of the {@link EntityManager}. An entity manager
33 * will be created when the unit of work is started. It is open and valid for use during the entire
34 * unit of work. When the unit of work ends the entity manager is closed and can no longer
35 * be used.
36 * <p/>
37 * It is a good practice to store this provider in a instance/member variable and only obtain an
38 * {@link EntityManager} instance in a method where it is used. This ensures that the method always
39 * has access to a valid {@link EntityManager}.
40 * <p/>
41 * The {@link EntityManagerProvider} is thread save.
42 */
43 public interface EntityManagerProvider extends Provider<EntityManager>
44 {
45
46 /**
47 * @return the {@link EntityManager}.
48 * @throws IllegalStateException if {@link UnitOfWork#isActive()} returns false.
49 */
50 EntityManager get()
51 throws IllegalStateException;
52
53 }