JPA中@javax.persistence.Lob注解的意义是什么? [英] What is the significance of @javax.persistence.Lob annotation in JPA?

问题描述

我什么时候应该在 JPA 中使用 @javax.persistence.Lob 注释?这个注解可以注解哪些数据类型?

解决方案

@javax.persistence.Lob 表示注解的字段应该在数据库中表示为 BLOB(二进制数据).

您可以使用此注释注释任何 Serializable 数据类型.在 JPA 中，在持久化(检索)字段内容时，将使用标准 Java 序列化来序列化(反序列化).

@Lob 的常见用途是在您的实体中注释一个 HashMap 字段，以存储一些未映射到 DB 列的对象属性.这样，所有未映射的值都可以以二进制表示形式存储在数据库中的一列中.当然，付出的代价是，由于它们以二进制格式存储，因此无法使用 JPQL/SQL 进行搜索.

When should I use @javax.persistence.Lob annotation in JPA? What datatypes can be annotated by this annotation?

解决方案

@javax.persistence.Lob signifies that the annotated field should be represented as BLOB (binary data) in the DataBase.

You can annotate any Serializable data type with this annotation. In JPA, upon persisting (retrieval) the field content will be serialized (deserialized) using standard Java serialization.

Common use of @Lob is to annotate a HashMap field inside your Entity to store some of the object properties which are not mapped into DB columns. That way all the unmapped values can be stored in the DB in one column in their binarry representation. Of course the price that is paid is that, as they are stored in binary format, they are not searchable using the JPQL/SQL.

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