Storing JSON objects in LDAP attributes…

jsonUntil recently, the only way to store a JSON object to an LDAP directory server, was to store it as string (either a Directory String i.e a sequence of UTF-8 characters, or an Octet String i.e. a blob of octets).

But now, in OpenDJ, the Open source LDAP Directory services in Java, there is now support for new syntaxes : one for JSON objects and one for JSON Query. Associated with the JSON query, a couple of matching rules, that can be easily customised and extended, have been defined.

To use the syntax and matching rules, you should first extend the LDAP schema with one or more new attributes, and use these attributes in object classes. For example :

dn: cn=schema
objectClass: top
objectClass: ldapSubentry
objectClass: subschema
attributeTypes: ( 1.3.6.1.4.1.36733.2.1.1.999 NAME 'json'
SYNTAX 1.3.6.1.4.1.36733.2.1.3.1 EQUALITY caseIgnoreJsonQueryMatch SINGLE-VALUE )
objectClasses: (1.3.6.1.4.1.36733.2.1.2.999 NAME 'jsonObject'
SUP top MUST (cn $ json ) )

Just copy the LDIF above into config/schema/95-json.ldif, and restart the OpenDJ server. Make sure you use your own OIDs when defining schema elements. The ones above are samples and should not be used in production.

Then, you can add entries in the OpenDJ directory server like this:

$ ldapmodify -a -D cn=directory\ manager -w secret12 -h localhost -p 1389

dn: cn=bjensen,ou=people,dc=example,dc=com
objectClass: top
objectClass: jsonObject
cn: bjensen
json: { "_id":"bjensen", "_rev":"123", "name": { "first": "Babs", "surname": "Jensen" }, "age": 25, "roles": [ "sales", "admin" ] }

dn: cn=scarter,ou=people,dc=example,dc=com
objectClass: top
objectClass: jsonObject
cn: scarter
json: { "_id":"scarter", "_rev":"456", "name": { "first": "Sam", "surname": "Carter" }, "age": 48, "roles": [ "manager", "eng" ] }

The very nice thing about the JSON syntax and matching rules, is that OpenDJ understands how the values of the json attribute are structured, and it becomes possible to make specific queries, using the JSON Query syntax.

Let’s search for all jsonObjects that have a json value with a specific _id :

$ ldapsearch -D cn=directory\ manager -w secret12 -h localhost -p 1389 -b "dc=example,dc=com" -s sub "(json=_id eq 'scarter')"

dn: cn=scarter,ou=people,dc=example,dc=com
objectClass: top
objectClass: jsonObject
json: { "_id":"scarter", "_rev":"456", "name": { "first": "Sam", "surname": "Carter" }, "age": 48, "roles": [ "manager", "eng" ] }
cn: scarter

We can run more complex queries, still using the JSON Query Syntax:

$ ldapsearch -D cn=directory\ manager -w secret12 -h localhost -p 1389 -b "dc=example,dc=com" -s sub "(json=name/first sw 'b' and age lt 30)"

dn: cn=bjensen,ou=people,dc=example,dc=com
objectClass: top
objectClass: jsonObject
json: { "_id":"bjensen", "_rev":"123", "name": { "first": "Babs", "surname": "Jensen" }, "age": 25, "roles": [ "sales", "admin" ] }
cn: bjensen

For a complete description of the query  filter expressions, please refer to ForgeRock Common  REST (CREST) Query Filter documentation.

The JSON matching rule supports indexing which can be enabled using dsconfig against the appropriate attribute index. By default all JSON fields of the attribute are indexed.

In a followup post, I will give more advanced configuration of the JSON Syntax, detail how to customise the matching rule to index only specific JSON fields, and will outline some best practices with the JSON syntax and attributes.

3 thoughts on “Storing JSON objects in LDAP attributes…

  1. Peter Major 24 October 2016 / 18:49

    Does the JSON support also allow retrieval of specific fields or portions of the JSON object stored? So for example could I construct a search request where I can retrieve the /sn JSON property of objects that have /_id=foobar?

    • Ludo 24 October 2016 / 19:37

      Hi Peter,
      Currently it is not possible to return a portion of the JSON objects, simply because the whole object is a single LDAP value. OpenDJ returns LDAP entries in which the attributes match the query filter. While there is a way to retrieve only the matching values, this is built as an extension and hardly used.

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