是否可以在Hibernate/JPA中动态定义列名？

Question

所以我有这个现有的数据库模式,其中包含许多我想用JPA/Hibernate建模的表.每个表具有相同的30个附加列组(以允许运行时扩展记录的字段数).

CREATE TABLE XX
  (
    "ID"          VARCHAR2(100 BYTE) NOT NULL ENABLE,
    "USER_LABEL"      VARCHAR2(256 BYTE),
    "CREATION_DATE"   NUMBER(38,0) NOT NULL ENABLE,
    "ADD_STR_FIELD_0" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_0" NUMBER(38,0),
    "ADD_DBL_FIELD_0" NUMBER(38,0),
    "ADD_STR_FIELD_1" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_1" NUMBER(38,0),
    "ADD_DBL_FIELD_1" NUMBER(38,0),
    "ADD_STR_FIELD_2" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_2" NUMBER(38,0),
    "ADD_DBL_FIELD_2" NUMBER(38,0),
    "ADD_STR_FIELD_3" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_3" NUMBER(38,0),
    "ADD_DBL_FIELD_3" NUMBER(38,0),
    "ADD_STR_FIELD_4" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_4" NUMBER(38,0),
    "ADD_DBL_FIELD_4" NUMBER(38,0),
    "ADD_STR_FIELD_5" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_5" NUMBER(38,0),
    "ADD_DBL_FIELD_5" NUMBER(38,0),
    "ADD_STR_FIELD_6" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_6" NUMBER(38,0),
    "ADD_DBL_FIELD_6" NUMBER(38,0),
    "ADD_STR_FIELD_7" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_7" NUMBER(38,0),
    "ADD_DBL_FIELD_7" NUMBER(38,0),
    "ADD_STR_FIELD_8" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_8" NUMBER(38,0),
    "ADD_DBL_FIELD_8" NUMBER(38,0),
    "ADD_STR_FIELD_9" VARCHAR2(200 BYTE),
    "ADD_LNG_FIELD_9" NUMBER(38,0),
    "ADD_DBL_FIELD_9" NUMBER(38,0),
}

我计划为每个表定义简单的类

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="XX")
public class XX {

    @Id
    Long id = null;
}

然后在公共类中定义公共附加参数

import javax.persistence.Column;

public abstract class AdditionalParameters {

    @Column(name="ADD_STR_FIELD_0")
    private String addStringField0 = null;
    @Column(name="ADD_LNG_FIELD_0")
    private Long addLongField0 = null;
    @Column(name="ADD_DBL_FIELD_0")
    private Double addDoubleField0 = null;
    ....
    ....
    ....
    @Column(name="ADD_STR_FIELD_8")
    private String addStringField8 = null;
    @Column(name="ADD_LNG_FIELD_8")
    private Long addLongField8 = null;
    @Column(name="ADD_DBL_FIELD_8")
    private Double addDoubleField8 = null;
}

虽然这会奏效,但我不喜欢班级的硬编码性质.

我想将每组字符串,长字段和双字段模型作为附加参数组,然后具有0..9组.如果需要,这将允许我稍后轻松添加额外的组.

如果我使用xml映射解决方案,我可以在为每个表生成.hbm.xml时动态确定正确的列名.我更喜欢使用带注释的解决方案,但有没有办法覆盖@Column getName()方法,以便我可以返回动态生成的列名？

Answer 1

您需要创建自定义NamingStrategy.

假设您在JPA中使用spring和hibernate,这是一个带有自定义NamingStrategy的配置代码段:

<bean id="entityManagerFactory"
    class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="persistenceUnitName" value="myunit" />
    <property name="dataSource" ref="dataSource" />
    <property name="persistenceXmlLocation"
              value="classpath:META-INF/persistence.xml" />
    <property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="showSql" value="false" />
            <property name="generateDdl" value="true" />
            <property name="database" value="MYSQL" />
        </bean>
    </property>
    <property name="jpaProperties">
        <props>
            <prop 
                key="hibernate.ejb.naming_strategy">
                com.yourcompany.CustomNamingStrategy
            </prop>
        </props>
    </property>
</bean>

如果不使用spring,配置会有所不同,但您仍然可以使用自定义NamingStrategy(请参阅从Hibernate文档实现NamingStrategy).

无论如何,这是一个示例NamingStrategy,它为连接表构建TYPE1_TYPE2形式的表名,并为所有表添加一个公共前缀:

public class CustomNamingStrategy extends ImprovedNamingStrategy {

    private static final long serialVersionUID = 1L;
    private static final String PREFIX = "PFX_";

    @Override
    public String classToTableName(final String className) {
        return this.addPrefix(super.classToTableName(className));
    }

    @Override
    public String collectionTableName(final String ownerEntity,
            final String ownerEntityTable, final String associatedEntity,
            final String associatedEntityTable, final String propertyName) {
        return this.addPrefix(super.collectionTableName(ownerEntity,
                ownerEntityTable, associatedEntity, associatedEntityTable,
                propertyName));
    }

    @Override
    public String logicalCollectionTableName(final String tableName,
            final String ownerEntityTable, final String associatedEntityTable,
            final String propertyName) {
        return this.addPrefix(super.logicalCollectionTableName(tableName,
                ownerEntityTable, associatedEntityTable, propertyName));
    }

    private String addPrefix(final String composedTableName) {

        return PREFIX
                + composedTableName.toUpperCase().replace("_", "");

    }

}