LDAP Datastore Mapping

When persisting a Java object to an LDAP datastore clearly the user would like some control over where and how in the LDAP DIT (directory information tree) we are persisting the object. In general Java objects are mapped to LDAP entries and fields of the Java objects are mapped to attributes of the LDAP entries.

Java Types

The following Java types are supported and stored as single-valued attribute to the LDAP entry:

  • String, primitives (like int and double), wrappers of primitives (like java.util.Long), java.util.BigDecimal, java.util.BigInteger, java.util.UUID
  • boolean and java.lang.Boolean are converted to RFC 4517 "boolean" syntax (TRUE or FALSE)
  • java.util.Date and java.util.Calendar are converted to RFC 4517 "generalized time" syntax
Arrays, Collections, Sets and Lists of these data types are stored as multi-valued attributes. Please note that when using Arrays and Lists no order could be guaranteed and no duplicate values are allowed!

Relationships

By default PersistenceCapable objects are stored as separate LDAP entries. There are some options how to persist relationship references between PersistenceCapable objects:

It is also possible to store PersistenceCapable objects embedded.

Examples

Here's an example using JDO XML MetaData: 

<jdo>
    <package name="org.datanucleus.samples.models.company">
        <class name="Group" table="ou=Groups,dc=example,dc=com" schema="top,groupOfNames" detachable="true">
            <field name="name" column="cn" primary-key="true" />
            <field name="users" column="member" />
        </class>

        <class name="Person" table="ou=Users,dc=example,dc=com" schema="top,person,organizationalPerson,inetOrgPerson" detachable="true">
            <field name="personNum" column="cn" primary-key="true" />
            <field name="firstName" column="givenMame" />
            <field name="lastName" column="sn" />
        </class>
    </package>
</jdo>

For the class as a whole we use the table attribute to set the distinguished name of the container under which to store objects of a type. So, for example, we are mapping all objects of class Group as subordinates to "ou=Groups,dc=example,dc=com". You can also use the extension "dn" to specify the same thing.

For the class as a whole we use the schema attribute to define the object classes of the LDAP entry. So, for example, all objects of type Person are mapped to the common "top,person,organizationalPerson,inetOrgPerson" object classes in LDAP. You can also use the extension "objectClass" to specify the same thing.

For each field we use the column attribute to define the LDAP attribute that we are mapping this field to. So, for example, we map the Group "name" to "cn" in our LDAP. You can also use the extension "attribute" to specify the same thing.

Some resulting LDAP entries would look like this: 

dn: cn=Sales,ou=Groups,dc=example,dc=com
objectClass: top
objectClass: groupOfNames
cn: Sales
member: cn=1,ou=Users,dc=example,dc=com

dn: cn=1,ou=Users,dc=example,dc=com
objectClass: top
objectClass: person
objectClass: organizationalPerson
objectClass: inetOrgPerson
cn: 1
givenName: Bugs
sn: Bunny

Here's the same example using JDO Annotations: 

@PersistenceCapable(table = "ou=Groups,dc=example,dc=com", schema = "top,groupOfNames")
public class Group
{
    @PrimaryKey
    @Column(name = "cn")
    String name;

    @Column(name = "member")
    protected Set<Person> users = new HashSet<Person>();
}

@PersistenceCapable(table = "ou=Users,dc=example,dc=com", schema = "top,person,organizationalPerson,inetOrgPerson")
public class Person
{
    @PrimaryKey
    @Column(name = "cn")
    private long personNum;

    @Column(name = "givenName")
    private String firstName;

    @Column(name = "sn")
    private String lastName;
}