@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.
j`ava.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:

"@Indexes"