EclipseLink/Examples/JPA/Indexes

EclipseLink (as of 2.2) provides a way to have a database INDEX generated when EclipseLink is used to generate the database. An index is used in a database to optimize queries that use that column to provide optimal look-up and avoid table scans. Different databases have different levels of index support, EclipseLink supports the creation of basic indexes on databases that support them. Normally databases auto-index primary key and foreign key fields, so normally these do not require indexes. Previous to EclipseLink 2.2, DDL scripts or native SQL queries could be used to defined indexes. These can also be used to define more complex indexes.

EclipseLink supports index creation using its @Index annotation or <index> xml element. The @Index has a name, schema, catalog, table, unique and a set of column names. An @Index can be put on any @Basic attribute and all of its properties will be defaulted to index the attribute's column. @Index can be set on a class to define a multi-column index. The @Indexes annotation can be used to define multiple indexes in one class.

To allow indexes to be generated DDL generation must be enabled. This is done through the "eclipselink.ddl-generation" persistence unit property, set to either "create-tables" or "drop-and-create-tables".

See also:

• @Index (EclipseLink JPA Extensions Reference)
• But what if I'm not querying by id? (database and cache indexes) (blog)

Example Index

The firstName and lastName are indexed, together and individually.

@Entity
@Index(name="EMP_NAME_INDEX", columnNames={"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;
    ...
}

This produces the SQL,

CREATE INDEX INDEX_EMPLOYEE_F_NAME ON EMPLOYEE (F_NAME)
CREATE INDEX INDEX_EMPLOYEE_L_NAME ON EMPLOYEE (L_NAME)
CREATE INDEX EMP_NAME_INDEX ON EMPLOYEE (F_NAME, L_NAME)