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我第一次将 JPA 与 Hibernate 一起使用，并尝试使用我的 Oracle 数据库中的现有序列设置自动 ID 生成。

我的实体映射如下所示：

<?xml version="1.0" encoding="UTF-8"?>
<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm"
        version="2.0">

    <entity class="AmmAdapter.DataAccessLayer.Models.AmmSyncTypePriorities">
        <table name="AMM_SYNC_TYPE_PRIORITIES" schema="TESTESTERON" catalog=""/>
        <attributes>
            <id name="id">
                <column name="ID" nullable="false" length="10"/>
                <generated-value strategy="SEQUENCE" generator="MODEL_SEQ"/>
                <sequence-generator name="MODEL_SEQ" sequence-name="AMM_ED_GROUP_TYPES_SEQ"/>
            </id>
            <basic name="priority">
                <column name="PRIORITY" nullable="false" length="10"/>
            </basic>
            <one-to-many name="ammSyncMessageTypesesById" mapped-by="ammSyncTypePrioritiesByPriority"
                         target-entity="AmmAdapter.DataAccessLayer.Models.AmmSyncMessageTypes"/>
        </attributes>
    </entity>
</entity-mappings>

我的 Java 类如下所示： package AmmAdapter.DataAccessLayer.Models;

import java.util.Collection;

public class AmmEdGroupTypes
{
    private Integer id;

    public Integer getId()
    {
        return id;
    }

    public void setId(Integer id)
    {
        this.id = id;
    }

    private String name;

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    @Override
    public boolean equals(Object o)
    {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        AmmEdGroupTypes that = (AmmEdGroupTypes)o;

        if (id != null ? !id.equals(that.id) : that.id != null) return false;
        if (name != null ? !name.equals(that.name) : that.name != null) return false;

        return true;
    }

    @Override
    public int hashCode()
    {
        int result = id != null ? id.hashCode() : 0;
        result = 31 * result + (name != null ? name.hashCode() : 0);
        return result;
    }

    private Collection<AmmEndDeviceGroups> ammEndDeviceGroupsesById;

    public Collection<AmmEndDeviceGroups> getAmmEndDeviceGroupsesById()
    {
        return ammEndDeviceGroupsesById;
    }

    public void setAmmEndDeviceGroupsesById(Collection<AmmEndDeviceGroups> ammEndDeviceGroupsesById)
    {
        this.ammEndDeviceGroupsesById = ammEndDeviceGroupsesById;
    }
}

我的序列 AMM_ED_GROUP_TYPES_SEQ 有：

最小值：1

最大值：9999999999999999999999999999

增量：1

我使用以下测试代码来确定自动生成是否正常工作： EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("AdapterPersistence");

EntityManager entityManager = entityManagerFactory.createEntityManager();

entityManager.getTransaction().begin();

AmmEdGroupTypes newGroup = new AmmEdGroupTypes();
newGroup.setName("test");

System.out.println(newGroup.getId());

结果我得到一个空 ID。有人知道问题是什么吗？

4

1 回答 1

2 
EntityManager entityManager = entityManagerFactory.createEntityManager();

entityManager.getTransaction().begin();

AmmEdGroupTypes newGroup = new AmmEdGroupTypes();
newGroup.setName("test");
entityManager.persist(newGroup);
entityManager.getTransaction().commit();
System.out.println(newGroup.getId());
于 2013-06-20T13:18:37.400 回答