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Difference between revisions of "EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Basic Mappings/Lob"

(Serialization)
(Example: @Lob)
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======'' Example: @Lob''======
 
======'' Example: @Lob''======
 
<source lang="java">
 
<source lang="java">
@Entity
+
@Entity
public class Employee implements Serializable {
+
public class Employee implements Serializable {
    ...
+
    ...
    @Lob
+
    @Lob
    @Basic(fetch=LAZY)
+
    @Basic(fetch=LAZY)
    @Column(name="EMP_PIC", columnDefinition="BLOB NOT NULL")
+
    @Column(name="EMP_PIC", columnDefinition="BLOB NOT NULL")
    protected byte[] pic;
+
    protected byte[] pic;
    ...
+
    ...
}
+
}
 
</source>
 
</source>
  

Revision as of 12:24, 27 October 2011

EclipseLink JPA

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Elug api package icon.png Key API


@Lob

By default, the EclipseLink persistence provider assumes that all persistent data can be represented as typical database data types.

Use the @Lob annotation with the @Basic mapping to specify that a persistent property or field should be persisted as a large object to a database-supported large object type.

A Lob may be either a binary or character type. The persistence provider infers the Lob type from the type of the persistent field or property.

For String and character-based types, the default is Clob. In all other cases, the default is Blob.

You can also use the @Column attribute columnDefinition to further refine the Lob type.

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For more information, see Section 11.1.9 "Column Annotation" in the JPA Specification.

The @Lob annotation does not have attributes.

The following example shows how to use this @Lob annotation to specify that persistent field pic should be persisted as a Blob.

Example: @Lob
@Entity
public class Employee implements Serializable {
    ...
    @Lob
    @Basic(fetch=LAZY)
    @Column(name="EMP_PIC", columnDefinition="BLOB NOT NULL")
    protected byte[] pic;
    ...
}
Elug javaspec icon.gif

For more information, see Section 11.1.24 "Lob Annotation" in the JPA Specification.

Serialization

Although a BLOB is stored as a byte[], the Java a type for a @Lob mapping can be any serializable type. JPA will automatically serialize and store the value into a BLOB field, and deserialize the value when read.

Lazy

If the LOB field is large, and may not always be required, it is normally a good idea to set its fetch type to LAZY using the @Basic annotation.

Database Limitations

Some database have size limitations for LOB fields, or requires large LOBs be written to the database in specific ways.

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Version: 2.1.0
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