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Java Persistence API (JPA) Extensions Reference for EclipseLink, Release 2.4
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@Index

An index is a database structure defined for a table, to improve query and look-up performance for a set of columns. Use the @Index annotation in code or the <index> element in the eclipselink-orm.xml descriptor to create an index on a table.

An index can be defined on an entity or on an attribute. For the entity it must define a set of columns to index.

Index creation is database specific. Some databases may not support indexes. Most databases auto-index primary key and foreign key columns. Some databases support advanced index DDL options. To create more advanced index DDL, a DDL script or native query can be used.


Annotation Elements

Table 2-26 describes this annotation's elements.

Table 2-26 @Index Annotation Elements

Annotation Element Description Default

java.lang.String catalog

(Optional) The catalog of the INDEX.

Default catalog

java.lang.String[] columnNames

(Not required when annotated on a field or method) Specify the set of columns to define the index on.

For an Entity, none.

For an attribute, the attribute's column.

java.lang.String name

(Optional) The name of the INDEX.

<table>_<column>_INDEX (but a name should be provided)

java.lang.String schema

(Optional) The schema of the INDEX.

Default schema

java.lang.String table

(Optional) The table to define the index on; defaults to entities primary table.

The entity's primary table.

boolean unique

(Optional) Specify whether the index is unique or non-unique.

false



Usage

Use @Index annotation to index any attributes or columns that will commonly be used in queries.


Examples

This example defines three indexes, one on first name, one on last name, and a multiple column index on first name and last name.

Example 2-48 Using @Index Annotation

@Entity
@Index(name="EMP_NAME_INDEX", columns={"F_NAME","L_NAME"})
public class Employee{
    @Id
    private long id;
    @Index
    @Column(name="F_NAME")
    private String firstName;
    @Index
    @Column(name="L_NAME")
    private String lastName;
    ...
}

You can also create an index in the eclipselink-orm.xml descriptor using <index>, as shown in the following example. Define columns using the <column> subelement. All the attributes supported in the @Index annotation are also supported in the <index> element.

Example 2-49 Using <index> XML

<index name="EMP_NAME_INDEX" table="EMPLOYEE" unique="true">
    <column>F_NAME</column>
    <column>L_NAME</column>
</index>


See Also

For more information see:

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