Java 使用 JPA 存储 Map<String,String>
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Storing a Map<String,String> using JPA
提问by corydoras
I am wondering if it is possible using annotations to persist the attributesmap in the following class using JPA2
我想知道是否可以使用注释将attributes地图保存在使用 JPA2 的以下类中
public class Example {
long id;
// ....
Map<String, String> attributes = new HashMap<String, String>();
// ....
}
As we already have a pre existing production database, so ideally the values of attributescould map to the following existing table:
由于我们已经有一个预先存在的生产数据库，因此理想情况下， 的值attributes可以映射到以下现有表：
create table example_attributes {
example_id bigint,
name varchar(100),
value varchar(100));
采纳答案by Pascal Thivent
JPA 2.0 supports collections of primitives through the @ElementCollectionannotation that you can use in conjunction with the support of java.util.Mapcollections.
Something like this should work:
JPA 2.0 通过@ElementCollection注解支持原语集合，您可以将这些注解与java.util.Map集合支持结合使用。这样的事情应该工作：
@Entity
public class Example {
@Id long id;
// ....
@ElementCollection
@MapKeyColumn(name="name")
@Column(name="value")
@CollectionTable(name="example_attributes", joinColumns=@JoinColumn(name="example_id"))
Map<String, String> attributes = new HashMap<String, String>(); // maps from attribute name to value
}
See also (in the JPA 2.0 specification)
另请参阅（在 JPA 2.0 规范中）
- 2.6 - Collections of Embeddable Classes and Basic Types
- 2.7 Map Collections
- 10.1.11 - ElementCollection Annotation
- 11.1.29 MapKeyColumn Annotation
- 2.6 - 可嵌入类和基本类型的集合
- 2.7 地图集合
- 10.1.11 - ElementCollection 注释
- 11.1.29 MapKeyColumn 注解
回答by wciesiel
@ElementCollection(fetch = FetchType.LAZY)
@CollectionTable(name = "raw_events_custom", joinColumns = @JoinColumn(name = "raw_event_id"))
@MapKeyColumn(name = "field_key", length = 50)
@Column(name = "field_val", length = 100)
@BatchSize(size = 20)
private Map<String, String> customValues = new HashMap<String, String>();
This is an example on how to set up a map with control over column and table names and field length.
这是一个关于如何设置映射以控制列和表名称以及字段长度的示例。
