如何同时创建两个相互引用的 Ebean 实体？答案

【问题标题】：How to create two Ebean entities referring to each other at the same time?如何同时创建两个相互引用的 Ebean 实体？
【发布时间】：2013-12-18 09:48:53
【问题描述】：

我有一个实体 CheckpointAnswer.java：

@Entity
public class CheckpointAnswer extends Model {

    @Id
    public Long id;

    @Column(length=160,nullable=false)
    public String answer;

    @ManyToOne
    public Checkpoint checkpoint;

    public CheckpointAnswer(String answer, Checkpoint checkpoint) {
        this.answer = answer;
        this.checkpoint = checkpoint;
    }

    public static Model.Finder<Long, CheckpointAnswer> find =
            new Finder<Long, CheckpointAnswer>(Long.class, CheckpointAnswer.class);
}

还有 Checkpoint.java：

@Entity
public class Checkpoint extends Model {

        @Id
        public Long id;

        @Column(length=80,nullable=false)
        public String name;

        @Column(nullable=false)
        public double longitude;

        @Column(nullable=false)
        public double latitude;

        @Column(nullable=false)
        public int points;

        @Column(length=160,nullable=false)
        public String message;

        @OneToMany
        public List<CheckpointAnswer> possibleAnswers = new ArrayList<CheckpointAnswer>();

        @ManyToOne
        public Scenario scenario;

        public Checkpoint(String name, double longitude, double latitude, int points, String message, List<String> answers, Scenario scenario) {
                this.name = name;
                this.longitude = longitude;
                this.latitude = latitude;
                this.points = points;
                this.message = message;
                this.scenario = scenario;
                for(String answer: answers) {
                        CheckpointAnswer ca = new CheckpointAnswer(answer, this);
                        ca.save();
                        possibleAnswers.add(ca);
                }
        }

        public static Model.Finder<Long, Checkpoint> find =
                new Finder<Long, Checkpoint>(Long.class, Checkpoint.class);

        public void addPossibleAnswer(String answer) {
                CheckpointAnswer checkpointAnswer = new CheckpointAnswer(answer, this);
                checkpointAnswer.save();
                this.possibleAnswers.add(checkpointAnswer);
                this.update();
        }

        public static List<Checkpoint> findAssignedTo(Long scenario) {
                return find.where()
                        .eq("scenario.id", scenario)
                        .findList();
        }
}

如何创建一个包含一些CheckpointAnswer 对象的Checkpoint 对象？没有CheckpointAnswer，Checkpoint 就不能存在，反之亦然。

我尝试了您可以在代码中看到的方法，但失败了。我有以下单元测试：

 @Test
 public void createAndRetrieveCheckpoint() {
     new User("bob@gmail.com", "Bob", "secret", "000000000", USER_PRIVILEGE.regular).save();
     Scenario scenario = Scenario.create("Scenario 1", false, null, "bob@gmail.com");

     List<String> answers = new ArrayList<String>();
     answers.add("test answer 1");
     new Checkpoint("test checkpoint", 21.456, 10.2, 10, "Test question for the user", answers, scenario).save();
     List<Checkpoint> checkpoints = Checkpoint.find.all();
     assertNotNull(checkpoints);
     assertEquals(1, checkpoints.size());
     assertNotNull(checkpoints.get(0).possibleAnswers);
     assertEquals(1, checkpoints.get(0).possibleAnswers);
}

结果：

[error] Test models.ModelsTest.createAndRetrieveCheckpoint failed: expected:<1> but was:<BeanList deferred >

【问题讨论】：

哪个测试失败了？ assertEquals(1, checkpoints.size()); 或 assertEquals(1, checkpoints.get(0).possibleAnswers);?
@mantithetical 第二个。

标签： java orm playframework ebean playframework-2.2

【解决方案1】：

假设 assertEquals(1, checkpoints.get(0).possibleAnswers); 失败，您可能想要：

assertEquals(1, checkpoints.get(0).possibleAnswers.size());

同样不相关，您不必将CheckpointAnswer 保存在Checkpoint 构造函数或addPossibleAnswers 中。当您保存Checkpoint 时，您的CheckpointAnswers 应该会被保留。这正是我们使用 ORM 的原因。这是cascades的一些信息。

【讨论】：