Storing & accessing nested structures in the Camunda context

Camunda 7 Topics Discussion & Questions
1

The data that we’re currently storing in the Camunda context is composed of nested java.util.Maps. Here’s how we correlate messages to the engine, along with passing the context:

Map<String, Object> context = <construct map>;
var builder = processEngine.getRuntimeService()
    .createMessageCorrelation(MESSAGE_NAME)
    .processInstanceVariablesEqual(CORRELATIONS)
    .setVariables(context);

The issue that we face at the moment is how to update only parts of the context. Lets say in a running process we have the following context:

vendingMachineId: "123",
inventory: [
    "coke": ["quantity": 1, price: "10"],
    "pepsi": ["quantity": 2, price: "5"]
]

The [:] syntax means a map. From what we read, the inventory would be stored as a LOB in the database. Is there a way to update only a part of this LOB? For example, to decrease the quantity of pepsi to 1, by correlating a message with the variables inventory: [pepsi: ["quantity": 1]]. Effectively performing a merge instead of a replace. Is there a way to customise how the context is updated?

One solution 1), or a workaround, that we found is to flatten the maps, so that the context looks like this:

vendingMachineId: "123",
inventory.coke.quantity: "1",
inventory.coke.price: "10",
inventory.pepsi.quantity: "2",
inventory.pepsi.price: "5"

In this case we can directly replace only inventory.pepsi.quantity. However, this brings the following disadvantages:

  • more load for the database for each running process, as each variable is a separate row
  • clumsier usage of the variables in the BPMN, as we can no longer directly use inventory.pepsi.price but have to call execution.getVariable('inventory.pepsi.price').

As an improvement we can introduce a custom function, lets say c, and call it in expressions - ${c('inventory').pepsi.price > 10. This way we can maintain a flattened context, as in solution 1), but at least make the bpmn usage slightly easier. Of course the desired expression would simply be ${inventory.pepsi.price}.

Kind regards,
Milan

1 Like
2

Being able to update parts of a map in a context would be helpful. I’m also interested to see if that’s possible and how to implement it (apart from having to perform manual correlation and update of the context).

3