[英]JPA Multiple Embedded fields
Is it possible for a JPA entity class to contain two embedded ( @Embedded
) fields? JPA实体类是否可以包含两个嵌入(
@Embedded
)字段? An example would be: 一个例子是:
@Entity
public class Person {
@Embedded
public Address home;
@Embedded
public Address work;
}
public class Address {
public String street;
...
}
In this case a Person
can contain two Address
instances - home and work. 在这种情况下,
Person
可以包含两个Address
实例 - home和work。 I'm using JPA with Hibernate's implementation. 我正在使用JPA和Hibernate的实现。 When I generate the schema using Hibernate Tools, it only embeds one
Address
. 当我使用Hibernate Tools生成模式时,它只嵌入一个
Address
。 What I'd like is two embedded Address
instances, each with its column names distinguished or pre-pended with some prefix (such as home and work). 我想要的是两个嵌入的
Address
实例,每个实例的列名都有区别或预先设置了一些前缀(例如家庭和工作)。 I know of @AttributeOverrides
, but this requires that each attribute be individually overridden. 我知道
@AttributeOverrides
,但这需要单独覆盖每个属性。 This can get cumbersome if the embedded object ( Address
) gets big as each column needs to be individually overridden. 如果嵌入对象(
Address
)变大,因为每个列都需要单独覆盖,这会很麻烦。
The generic JPA way to do it is with @AttributeOverride. 通用的JPA方法是使用@AttributeOverride。 This should work in both EclipseLink and Hibernate.
这应该在EclipseLink和Hibernate中都有效。
@Entity
public class Person {
@AttributeOverrides({
@AttributeOverride(name="street",column=@Column(name="homeStreet")),
...
})
@Embedded public Address home;
@AttributeOverrides({
@AttributeOverride(name="street",column=@Column(name="workStreet")),
...
})
@Embedded public Address work;
}
@Embeddable public class Address {
@Basic public String street;
...
}
}
If you want to have the same embeddable object type twice in the same entity, the column name defaulting will not work: at least one of the columns will have to be explicit. 如果要在同一实体中两次使用相同的可嵌入对象类型,则列名默认将不起作用:至少有一列必须是显式的。 Hibernate goes beyond the EJB3 spec and allows you to enhance the defaulting mechanism through the NamingStrategy.
Hibernate超越了EJB3规范,允许您通过NamingStrategy增强默认机制。 DefaultComponentSafeNamingStrategy is a small improvement over the default EJB3NamingStrategy that allows embedded objects to be defaulted even if used twice in the same entity.
DefaultComponentSafeNamingStrategy是对默认EJB3NamingStrategy的一个小改进,即使在同一实体中使用两次,也允许默认嵌入对象。
From Hibernate Annotations Doc: http://docs.jboss.org/hibernate/stable/annotations/reference/en/html_single/#d0e714 来自Hibernate Annotations Doc: http : //docs.jboss.org/hibernate/stable/annotations/reference/en/html_single/#d0e714
When using Eclipse Link, an alternative to using AttributeOverrides it to use a SessionCustomizer. 使用Eclipse Link时,使用AttributeOverrides的替代方法是使用SessionCustomizer。 This solves the issue for all entities in one go:
这一次解决了所有实体的问题:
public class EmbeddedFieldNamesSessionCustomizer implements SessionCustomizer {
@SuppressWarnings("rawtypes")
@Override
public void customize(Session session) throws Exception {
Map<Class, ClassDescriptor> descriptors = session.getDescriptors();
for (ClassDescriptor classDescriptor : descriptors.values()) {
for (DatabaseMapping databaseMapping : classDescriptor.getMappings()) {
if (databaseMapping.isAggregateObjectMapping()) {
AggregateObjectMapping m = (AggregateObjectMapping) databaseMapping;
Map<String, DatabaseField> mapping = m.getAggregateToSourceFields();
ClassDescriptor refDesc = descriptors.get(m.getReferenceClass());
for (DatabaseMapping refMapping : refDesc.getMappings()) {
if (refMapping.isDirectToFieldMapping()) {
DirectToFieldMapping refDirectMapping = (DirectToFieldMapping) refMapping;
String refFieldName = refDirectMapping.getField().getName();
if (!mapping.containsKey(refFieldName)) {
DatabaseField mappedField = refDirectMapping.getField().clone();
mappedField.setName(m.getAttributeName() + "_" + mappedField.getName());
mapping.put(refFieldName, mappedField);
}
}
}
}
}
}
}
}
In case you are using hibernate you can also use a different naming scheme which adds unique prefixes to columns for identical embedded fields. 如果您正在使用休眠,您还可以使用不同的命名方案,为相同的嵌入字段的列添加唯一的前缀。 See Automatically Add a Prefix to Column Names for @Embeddable Classes
请参阅自动为@Embeddable类的列名添加前缀
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