!!! Overview
[{$pagename}] ([1.3.6.1.4.1.30221.2.5.9]) describes the relationship that you want to use to identify other [LDAP Entries|LDAP Entry] that are in some way related to the entries matching your [SearchRequest].


the following ASN.1 encoding:
{{{
 LDAPJoin ::= SEQUENCE {
     joinRule         JoinRule,
     baseObject       CHOICE {
          useSearchBaseDN      [0] NULL,
          useSourceEntryDN     [1] NULL,
          useCustomBaseDN      [2] LDAPDN,
          ... },
     scope            [0] ENUMERATED {
          baseObject             (0),
          singleLevel            (1),
          wholeSubtree           (2),
          subordinateSubtree     (3),
          ... } OPTIONAL,
     derefAliases     [1] ENUMERATED {
          neverDerefAliases       (0),
          derefInSearching        (1),
          derefFindingBaseObj     (2),
          derefAlways             (3),
          ... } OPTIONAL,
     sizeLimit        [2] INTEGER (0 .. maxInt) OPTIONAL,
     filter           [3] Filter OPTIONAL,
     attributes       [4] AttributeSelection OPTIONAL,
     requireMatch     [5] BOOLEAN DEFAULT FALSE,
     nestedJoin       [6] LDAPJoin OPTIONAL,
     ... }

JoinRule ::= CHOICE {
     and               [0] SET (1 .. MAX) of JoinRule,
     or                [1] SET (1 .. MAX) of JoinRule,
     dnJoin            [2] AttributeDescription,
     equalityJoin      [3] JoinRuleAssertion,
     containsJoin      [4] JoinRuleAssertion,
     reverseDNJoin     [5] AttributeDescription,
     ... }

JoinRuleAssertion ::= SEQUENCE {
     sourceAttribute     AttributeDescription,
     targetAttribute     AttributeDescription,
     matchAll            BOOLEAN DEFAULT FALSE }
}}}     
Most of the fields of the join request should be familiar because they’re similar to the fields of an ordinary search request. Also note that the Javadoc for the JoinRequestControl, JoinRequestValue, JoinRule, and JoinBaseDN classes in the [UnboundID LDAP SDK For Java] may provide additional information.

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [The LDAP Join Control in the Ping Identity Directory Server|https://nawilson.com/2019/02/14/the-ldap-join-control-in-the-ping-identity-directory-server/|target='_blank'] - based on information obtained 2019-03-19