Creating a Dynamic Variable

This guide walks through the steps to create a dynamic variable in a value library using the Rules Designer. Dynamic variables allow you to externalize configuration values that can be overridden at runtime.

Prerequisites

  • MPS (version 2022.3.1)

  • A model using the com.iconsolutions.simple.devkit, or a devkit that uses it

Steps

1. Create or Open a Value Library

Dynamic variables are defined within value libraries. If you don’t have one already, create a new value library by right-clicking on your model in the Logical View and navigating to New > com.iconsolutions.simple > Value Library.

create dynamic variable step 1 1

If creating a new Dynamic Variable Library, then make sure to name it.

create dynamic variable step 1 2

2. Add a Dynamic Variable

Within the value library, create a new entry by placing the cursor on the Dynamic Variable table, or where it says <no declarations> (if no variables have been defined); and press Enter. A new row in the table will be created with empty column elements ready to be defined.

create dynamic variable step 2

3. Name the Variable

Give your dynamic variable a descriptive name. This name will be combined with the model name to form the configuration key.

For example, if your model is named paymentService and you name the variable upperBound, the configuration key will be paymentService_upperBound.

create dynamic variable step 3

4. Set the Type

Specify the type of your dynamic variable. Supported types are:

  • number - for numeric values

  • string - for text values

  • boolean - for true/false values

  • list<number> - for lists of numbers

  • list<string> - for lists of strings

  • list<boolean> - for lists of booleans

Press Ctrl+Space in the type field to see available options.

create dynamic variable step 4

5. Set the Default Value

Every dynamic variable must have a default value. This value is used when no configuration override is provided at runtime.

Enter an appropriate default value for your type:

  • Numbers: 1000, 3.14

  • Strings: "USD"

  • Booleans: true, false

  • Lists: [1, 2, 3], ["USD", "EUR"]

create dynamic variable step 5

6. Set the Description

Finally, a description should be added to explain what the variable is for, or any other important information related to it.

create dynamic variable step 6

7. Complete Example

A completed value library with multiple dynamic variables might look like this:

create dynamic variable step 7

In this example:

  • exampleString is a string with default "example"

  • exampleInt is an int with default 1

  • exampleBoolean is a boolean with default true

  • exampleStringList is a list of strings with default ["a", "b", "c"]

Generated Code

When you build your model, MPS generates a class that implements DynamicVariablesLibrary, containing:

  • Static DynamicVariable<T> constants for each variable

  • A singleton INSTANCE

  • A getDynamicVariables() method returning all variables

public class ExampleDynamicVariablesLib implements DynamicVariableLibrary {

    public static final DynamicVariable<String> exampleString =
        new DynamicVariable<>("exampleModel", "exampleString",
            String.class, "example");

    // ... other DynamicVariable static declarations

    private final List<DynamicVariable<?>> dynamicVariables;

    public static DynamicVariableLibrary INSTANCE = new ExampleDynamicVariablesLib();
    private ExampleDynamicVariablesLib() {
        dynamicVariables = new ArrayList<>();
        dynamicVariables.add(exampleString);
        // ... adds other DynamicVariables
    }


    public static DynamicVariable<?> valueOf(String name) {
        switch(name) {
            case "exampleString":
                return exampleString;
            // ... other DynamicVariable cases
            default:
                return null;
        }
    }

    @Override
    public List<DynamicVariable<?>> getDynamicVariables() {
        return dynamicVariables;
    }
}

Next Steps

After creating your dynamic variables:

  1. Build your MPS model to generate the Java code

  2. Configure override values using HOCON configuration or via another dynamic value source.

  3. Use the variables in your business rules - see Using Dynamic Variables in Business Rules

Additional Resources