java – 如何从Hibernate MetadataSources中发现完全限定的表列

发布时间：2020-12-15 00:58:48 所属栏目：Java 来源：网络整理

导读：我有一个实体,我有一个Class MyEntity参考： @Entityclass MyEntity { @Id int id; @Column String col1; @Column(name = "abc") String col2;} 我目前正在使用Hibernate将我的实体导出到内存数据库中,如下所示： MetadataSources metadata = new MetadataSo

我有一个实体,我有一个Class< MyEntity>参考：

@Entity
class MyEntity {
    @Id int id;
    @Column String col1;
    @Column(name = "abc") String col2;
}

我目前正在使用Hibernate将我的实体导出到内存数据库中,如下所示：

MetadataSources metadata = new MetadataSources(...);
metadata.addAnnotatedClass(MyEntity.class);
SchemaExport export = new SchemaExport();
export.create(EnumSet.of(TargetType.DATABASE),metadata.buildMetadata());

Details about the Hibernate-specific API here.

有没有可靠的方法通过Hibernate API从MyEntity.col2(带注释的Java字段引用)到数据库中的完全限定列名(反之亦然)获取映射？在没有明确限定的情况下,我想避免重新实现Java标识符(包括getter和setter)如何映射到SQL标识符的所有细节.

解决方法

这是一个非常好的问题,所以我决定将 an article用于更详细地回答它.

org.hibernate.boot.Metadata是我们感兴趣的,因为它包含PersistentClass实体绑定.

首先,您需要创建一个Integrator来访问元数据：

public class MetadataExtractorIntegrator 
    implements org.hibernate.integrator.spi.Integrator {

    public static final MetadataExtractorIntegrator INSTANCE = 
        new MetadataExtractorIntegrator();

    private Database database;

    private Metadata metadata;

    public Database getDatabase() {
        return database;
    }

    public Metadata getMetadata() {
        return metadata;
    }

    @Override
    public void integrate(
            Metadata metadata,SessionFactoryImplementor sessionFactory,SessionFactoryServiceRegistry serviceRegistry) {

        this.database = metadata.getDatabase();
        this.metadata = metadata;

    }

    @Override
    public void disintegrate(
        SessionFactoryImplementor sessionFactory,SessionFactoryServiceRegistry serviceRegistry) {

    }
}

如果您使用JPA,您可以按如下方式注册：

Map<String,Object> configuration = new HashMap<>();

Integrator integrator = integrator();
if (integrator != null) {
    configuration.put("hibernate.integrator_provider",(IntegratorProvider) () -> Collections.singletonList(
            MetadataExtractorIntegrator.INSTANCE
        )
    );
}

EntityManagerFactory entityManagerFactory = new EntityManagerFactoryBuilderImpl(
    new PersistenceUnitInfoDescriptor(persistenceUnitInfo),configuration
)
.build();

现在,在运行以下测试用例时：

Metadata metadata = MetadataExtractorIntegrator.INSTANCE.getMetadata();

for ( PersistentClass persistentClass : metadata.getEntityBindings()) {

    Table table = persistentClass.getTable();

    LOGGER.info( "Entity: {} is mapped to table: {}",persistentClass.getClassName(),table.getName()
    );

    for(Iterator propertyIterator = persistentClass.getPropertyIterator(); 
            propertyIterator.hasNext(); ) {
        Property property = (Property) propertyIterator.next();

        for(Iterator columnIterator = property.getColumnIterator(); 
                columnIterator.hasNext(); ) {
            Column column = (Column) columnIterator.next();

            LOGGER.info( "Property: {} is mapped on table column: {} of type: {}",property.getName(),column.getName(),column.getSqlType()
            );
        }
    }
}

反对以下实体：

我们得到以下输出：

Entity: com.vladmihalcea.book.hpjp.util.providers.entity.BlogEntityProvider$Tag is mapped to table: tag
Property: name is mapped on table column: name of type: varchar(255)
Property: version is mapped on table column: version of type: integer

Entity: com.vladmihalcea.book.hpjp.util.providers.entity.BlogEntityProvider$PostComment is mapped to table: post_comment
Property: post is mapped on table column: post_id of type: bigint
Property: review is mapped on table column: review of type: varchar(255)
Property: version is mapped on table column: version of type: integer

Entity: com.vladmihalcea.book.hpjp.util.providers.entity.BlogEntityProvider$Post is mapped to table: post
Property: title is mapped on table column: title of type: varchar(255)
Property: version is mapped on table column: version of type: integer

Entity: com.vladmihalcea.book.hpjp.util.providers.entity.BlogEntityProvider$PostDetails is mapped to table: post_details
Property: createdBy is mapped on table column: created_by of type: varchar(255)
Property: createdOn is mapped on table column: created_on of type: datetime(6)
Property: version is mapped on table column: version of type: integer

很酷,对吗？

您也可以查看此示例on GitHub.

（编辑：李大同）

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