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

Question

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：

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 获取从 MyEntity.col2（带注释的 Java 字段引用）到数据库中完全限定的列名（反之亦然）的映射？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 标识符的所有微妙细节。

Answer 1

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，它可以让您访问Metadata：

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) {
 
    }
}

如果你使用JPA，可以如下注册：

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()
            );
        }
    }
}

针对以下实体：

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，对吧？

您也可以查看此示例 on GitHub。