CODEWITHSUNDEEP
javajpaannotationsjava-ee-7
Dev
Dev

Reputation: 13753

What is the significance of @javax.persistence.Lob annotation in JPA?

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

Upvotes: 68

Views: 68619

Answers (3)

Zielu
Zielu

Reputation: 8552

@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 database columns. That way, all the unmapped values can be stored in the database in one column in their binary 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.

Upvotes: 73

masikkk
masikkk

Reputation: 51

In my JPA + mysql test, java entity class field annotated with @Lob will generated longtext mysql column by auto ddl.

Upvotes: 3

levrun
levrun

Reputation: 283

According to: https://docs.oracle.com/javaee/7/api/javax/persistence/Lob.html

@Lob Specifies that a persistent property or field should be persisted as a large object to a database-supported large object type.

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

I suppose in database it could be not only binary data but character-based. As we could have BLOB and CLOB. Here's examples in java code:

@Lob
@Column(name = "CHARS", columnDefinition = "CLOB")
private String chars;`

@Lob
@Basic(fetch = FetchType.LAZY)
@Column(name = "DATA", columnDefinition = "BLOB", nullable = false)
private byte[] data;

Upvotes: 27

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