java - Hibernate - 使用生成的复合键插入临时子实体

Question

我在使用 Hibernate 插入一堆临时子实体时遇到问题，这些临时子实体可能具有由其他临时子实体组成的复合键，方法是保存分离的父实体。我很确定我的复合键类设置正确，但每次我尝试保存具有 transient 实体(尚未生成 ID)的父实体时，我都会收到此错误:

org.hibernate.id.IdentifierGenerationException: null id generated for:class org._.website.data.entity.Mean

所以 Hibernate 从不生成 Composite 键，我认为它应该能够给出被引用的属性。但是，由于复合键引用的属性也是暂时的，因此没有 ID 可用于手动设置复合键。所以我希望 Hibernate 足够聪明，可以自己生成。

有没有办法让 Hibernate 处理带有引用其他 transient 子实体的复合键的 transient 子实体的保存/插入？

这是我正在使用的代码。如果在 projectDao.save(project) 上失败；

Variable variable = new Variable();
variable.setProject(project);
variable.setName("x");

Belief belief = new Belief();
belief.setProject(project);
belief.setName("model-1");

Mean mean = new Mean();
mean.setVariable(variable);
mean.setBelief(belief);

// I can't do this because variable and belief are transient and have no ID yet
//MeanPK meanPk = new MeanPK(variableId, beliefId);
//mean.setPk(meanPk);

belief.getMeans().add(mean);

project.getVariables().add(variable);
project.getBeliefs().add(belief);

projectDao.save(project);

如果有帮助，这里是 Embeddable MeanPK 类

@Embeddable
public static class MeanPK implements Serializable {

    private static final long serialVersionUID = 341373316515655834L;

    @GeneratedValue
    @Column(name = "belief_id", nullable = false, updatable = false)
    protected Integer beliefId;

    @GeneratedValue
    @Column(name = "variable_id", nullable = false, updatable = false)
    protected Integer variableId;

    // getters/setters excluded for brevity

    @Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (!(obj instanceof MeanPK)) {
            return false;
        }
        MeanPK other = (MeanPK) obj;
        return beliefId.equals(other.beliefId) && variableId.equals(other.variableId);
    }

    @Override
    public int hashCode() {
        return new HashCodeBuilder().append(beliefId).append(variableId).toHashCode();
    }

}

如果绝对必要，我可以先保存复合键引用的 transient 实体以获取 ID 并手动构建 MeanPK 复合键，但我希望 Hibernate 能够通过单个调用 projectDao.save(...);

感谢您的帮助!

Answer 1

我想出了我的问题的答案，我想我会发布它以防有人发现它有用。

我所做的是在将引用的 Variable 和 Belief 实体设置为 Mean 实体时将它们存储在 MeanPK 类本身中。我向 MeanPk 类中的 ID getter 添加了一些逻辑，以便当它们被 hibernate 调用时，它将首先检查以设置存储在 MeanPK 类中的对象的 id。这是有效的，因为 hibernate 将在到达 Mean 实体之前插入并保留 transient Variable 和 Belief 实体，因为它是最底层的子实体。我的所有集合都有 CascadeType.ALL，所以我不需要担心手动保存每个实体，Hibernate 会将保存操作从父级级联到子级。

这是更新后的 MeanPK 类和 Mean 实体类:

@Entity
@Table(name = "mean")
public class Mean implements Serializable {

    private static final long serialVersionUID = -5732898358425089380L;


    // composite key
    @EmbeddedId
    private MeanPK pk = new MeanPK();

    @ManyToOne(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH })
    @JoinColumn(name = "belief_id", insertable = false, nullable = false, updatable = false)
    private Belief belief;

    @ManyToOne(fetch = FetchType.LAZY, cascade = { CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH })
    @JoinColumn(name = "variable_id", insertable = false, nullable = false, updatable = false)
    private Variable variable;

    // more attributes excluded

    public MeanPK getPk() {
        return pk;
    }

    protected void setPk(MeanPK pk) {
        this.pk = pk;
    }


    public Belief getBelief() {
        return belief;
    }

    public void setBelief(Belief belief) {
        pk.setBelief(this.belief = belief);
    }


    @XmlTransient
    public Variable getVariable() {
        return variable;
    }

    public void setVariable(Variable variable) {
        pk.setVariable(this.variable = variable);
    }


    @Embeddable
    public static class MeanPK implements Serializable {

        private static final long serialVersionUID = 341373316515655834L;

        @Access(AccessType.PROPERTY)
        @Column(name = "belief_id", nullable = false, updatable = false)
        protected Integer beliefId;

        @Access(AccessType.PROPERTY)
        @Column(name = "variable_id", nullable = false, updatable = false)
        protected Integer variableId;

        @Transient
        private Belief belief;

        @Transient
        private Variable variable;


        public Integer getBeliefId() {
            if (beliefId == null && belief != null) {
                beliefId = belief.getId();
            }
            return beliefId;
        }

        protected void setBeliefId(Integer beliefId) {
            this.beliefId = beliefId;
        }

        public Belief getBelief() {
            return belief;
        }

        void setBelief(Belief belief) {
            this.belief = belief;
            if (belief != null) {
                beliefId = belief.getId();
            }
        }


        public Integer getVariableId() {
            if (variableId == null && variable != null) {
                variableId = variable.getId();
            }
            return variableId;
        }

        protected void setVariableId(Integer variableId) {
            this.variableId = variableId;
        }

        public Variable getVariable() {
            return variable;
        }

        void setVariable(Variable variable) {
            this.variable = variable;
            if (variable != null) {
                variableId = variable.getId();
            }
        }


        @Override
        public boolean equals(Object obj) {
            if (obj == this) {
                return true;
            }
            if (!(obj instanceof MeanPK)) {
                return false;
            }
            MeanPK other = (MeanPK) obj;
            return getBeliefId().equals(other.getBeliefId()) && getVariableId().equals(other.getVariableId());
        }

        @Override
        public int hashCode() {
            return new HashCodeBuilder().append(getBeliefId()).append(getVariableId()).toHashCode();
        }

    }

}