OpenIDM: Sequential Number Generator

The problem 

Working on a Proof of Concept recently the customer wanted numbers to be allocated to new users in sequence. They wanted the sequence to start at 300000000 and increase by 1 each time a new user was created. This was to 'guarantee' uniqueness of the number allocated to each user.

The solution

I decided to make use of the generic repository object capability of OpenIDM. This is a little known feature but something I've blogged about in the past (See: http://yaunap.blogspot.co.uk/2015/09/data-driven-preferences-list-in-openidm.html) But just storing a number wasn't enough...I needed some logic to increment the number and store the result, as well as an API in order to 'GetNextId' when a new user was created.
So there are several parts to this:

1. Repository Object 
2. Script to read stored number, increment it, store it and return it 
3. Custom endpoint in OpenIDM to expose the script to clients 

Repository object 

Creating the repository object is straightforward. I called my object 'counter'. It will have a single field/value called 'lastid' seeded with 300000000 (note limitation below):

curl --header "X-OpenIDM-Username: openidm-admin" --header "X-OpenIDM-Password: openidm-admin"  --header "Content-Type: application/json" --data '{"lastid":"300000000" }' --request POST http://localhost:8080/openidm/repo/counter?_action=create

Script

The script is also fairly simple:

(function getNextId () {
  //read last number from custom repo object, add 1, store it back, return it!
  var  lastid = (openidm.read('repo/counter/lastid'));
  var nextid = Number(lastid['lastid']) + 1;
  lastid['lastid'] = nextid;
  openidm.update('repo/counter/lastid',null,lastid);
  return {nextid:nextid.toString()};
}());

This needs to be saved to a new .js file in the 'script' directory under the OpenIDM deployment directory. e.g. openidm/script/getNextId.js

Custom Endpoint

The custom endpoint is a simple definition (creating custom endpoints is well documented in the Integrators Guide):

{
    "type" : "text/javascript",
    "file" : "script/getNextId.js"
} 

 This needs to be saved to a .json file in the 'conf' directory. The naming convention is important. It must start with 'endpoint-'. Anything after the '-' will be the name of API you can access over HTTP. Therefore a file called:
openidm/conf/endpoint-getnextid.json
will be addressable thus:

curl -H "X-OpenIDM-Username: openidm-admin" -H "X-OpenIDM-Password: openidm-admin" 'http://localhost:8080/openidm/endpoint/getnextid'

Limitation: 

The endpoint only handles javascript numbers with values less than 2147483648 If you want larger numbers (i.e. starting at 3000000000) then the logic will need to support some way of handling the larger number.

Counter Reset:

To reset the counter, use:

curl --header "X-OpenIDM-Username: openidm-admin" --header "X-OpenIDM-Password: openidm-admin"  --header "Content-Type: application/json" --data '{"lastid":"300000000" }' --header "If-Match: *" --request PUT http://localhost:8080/openidm/repo/counter/lastid