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EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Basic Mappings/Lob

< EclipseLink‎ | UserGuide‎ | JPA‎ | Basic JPA Development‎ | Mapping‎ | Basic Mappings
Revision as of 14:36, 27 October 2011 by (Talk | contribs) (Database Limitations)

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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
public class Employee implements Serializable {
    @Column(name="EMP_PIC", columnDefinition="BLOB NOT NULL")
    protected byte[] pic;
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For more information, see Section 11.1.24 "Lob Annotation" in the JPA Specification.


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.


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

EclipseLink supports using a LOB locator to write LOBs on Oracle. This was required to write LOBs > 4k when using the Oracle JDBC thin driver until Oracle 11g. If the Oracle8Platform or higher (until Oracle11Platform) is used LOBs will be written using a locator. This can be configured in the database platform.

EclipseLink by default binds LOB values as byte[] or String. Some databases or JDBC drivers may require stream binding. Stream binding can be configured in the database platform in code, using a SessionCustomizer

Version: 2.1.0
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