Indexes are database structures that speed up searches, similar to how the index of a book helps you find what you're looking for. Placing indexes on columns that you often use in queries can drastically improve query performance. Note that primary key columns and columns with a physical foreign key are already naturally indexed by the database; you do not need to place additional indexes on them.

JDOR only uses index markup for table creation; it is not used at runtime. If you are mapping your classes to existing tables, you do not have to denote your existing indexes in the mapping metadata.

As with foreign keys, JDOR allows you to specify an index with either an attribute or an element. In the attribute-based approach, you place the indexed attribute on the mapping element whose columns you want to index. This attribute recognizes the values true, false, and unique. A unique index assumes that the combined data in the index's columns is unique for each row. The following mapping elements accept the indexed attribute: discriminator, version, field, join, element, key, value, order.

<class name="Article" table="ART">
    <field name="title" column="TITLE" indexed="true"/>
    ...
</class>

In place of the indexed attribute, you can use a contextual index element. Any element that accepts the indexed attribute also accepts a nested index element. The element goes after any nested columns and foreign-keys. It has the following attributes:

The index element also permits nested extension elements.

Here is the previous example with an index element in place of the indexed attribute:

<class name="Article" table="ART">
    <field name="title" column="TITLE">
        <index name="ART_TTL_IDX"/>
    </field>
    ...
</class>