是否可以在 Hibernate/JPA 中动态定义列名? [英] Is it possible to dynamically define column names in Hibernate / JPA?

问题描述

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(以允许运行时扩展字段数记录).

So i have this existing DB schema with a number of tables that i want to model with JPA/Hibernate. Each table has the same group of 30 additional columns ( to allow for runtime expansion of the number of fields recorded).

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),
}

我打算为每个表定义简单的类

I plan to define simple classes for each table

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

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

    @Id
    Long id = null;
}

然后在通用类中定义通用的附加参数

and then define the common additional parameters in a common class

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;
}

虽然这行得通，但我不喜欢类的硬编码性质.

while this will work, i don't like the hardcoded nature of the class.

我想将每组字符串、长字段和双字段建模为一个附加参数组，然后有 0..9 组.如果需要，这将允许我稍后轻松添加额外的组.

I would like to model each set of string,long and double fields as an additional parameter group, and then have 0..9 groups. This would allow me easily add extra groups later if required.

如果我使用 xml 映射解决方案，我可以在生成 .hbm.xml 时动态确定正确的列名每张桌子.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?

If i use the xml mapping solution i can dynamically determine the correct column name when generating the .hbm.xml for each table. I would prefer to use an annotated solution, but is there a way to override the @Column getName() method so that i can return a dynamically generated column name?

推荐答案

你需要创建一个自定义的 NamingStrategy.

You need to create a custom NamingStrategy.

假设您在 JPA 中使用 spring 和 hibernate，这里是一个带有自定义 NamingStrategy 的配置片段:

Assuming you use spring and hibernate with JPA, here is a configuration snippet with a custom NamingStrategy:

<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>

如果你不使用spring，配置会有所不同，但你仍然可以使用自定义的NamingStrategy(参见实现命名策略 来自 Hibernate 文档).

If you don't use spring, configuration will be different, but you can still use a custom NamingStrategy (see Implementing a NamingStrategy from the Hibernate Documentation).

无论如何，这里有一个示例 NamingStrategy，它为连接表构建了 TYPE1_TYPE2 形式的表名，并为所有表添加了一个公共前缀:

Anyway, here is a sample NamingStrategy that builds table names of the form TYPE1_TYPE2 for join tables and adds a common prefix to all tables:

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("_", "");

    }

}

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