Evaluate a Decision Table with Lookup

This example shows how to combine the evaluation of a decision table with lookup functionality, offering you a powerful tool for data processing and decision-making. By incorporating lookup capabilities, you can retrieve additional information or make data-driven decisions based on external data sources, enhancing the decision-making process within the evaluation of the decision table.

Java Code Listing

package com.northconcepts.datapipeline.foundations.examples.decisiontable;

import com.northconcepts.datapipeline.core.FieldList;
import com.northconcepts.datapipeline.core.Record;
import com.northconcepts.datapipeline.foundations.decisiontable.DecisionTable;
import com.northconcepts.datapipeline.foundations.decisiontable.DecisionTableResult;
import com.northconcepts.datapipeline.foundations.decisiontable.DecisionTableRule;
import com.northconcepts.datapipeline.internal.expression.DefaultExpressionContext;
import com.northconcepts.datapipeline.transform.lookup.BasicLookup;
import com.northconcepts.datapipeline.transform.lookup.Lookup;

public class EvaluateADecisionTableWithLookup {

    public static void main(String[] args) {
        DefaultExpressionContext input = new DefaultExpressionContext();
        input.setValue("Price", 159);
        input.setValue("Currency Code", "cad");

        Lookup currencyLookup = new BasicLookup(new FieldList("Currency Name"))
                .add("CAD", "Canadian Dollars")
                .add("USD", "American Dollars")
                .add("EUR", "Euros")
                .add("GBP", "British Pounds")
                .add("MXN", "Mexican Pesos")
                ;
        
        DecisionTable table = new DecisionTable()
                .setValue("currencyLookup", currencyLookup)
                .addRule(new DecisionTableRule()
                        .addCondition("Price", "? == null || ? < 20")
                        .addOutcome("Shipping", "0.00")
                        .addOutcome("Currency", "lookup(0, currencyLookup, toUpperCase(${Currency Code}))")
                        )
                .addRule(new DecisionTableRule()
                        .addCondition("Price", "? < 50")
                        .addOutcome("Shipping", "5.00")
                        .addOutcome("Currency", "lookup(0, currencyLookup, toUpperCase(${Currency Code}))")
                        )
                .addRule(new DecisionTableRule()
                        .addCondition("Price", "? < 100")
                        .addOutcome("Shipping", "7.00")
                        .addOutcome("Currency", "lookup(0, currencyLookup, toUpperCase(${Currency Code}))")
                        )
                .addRule(new DecisionTableRule()
                        .addCondition("Price", "? >= 100")
                        .addOutcome("Shipping", "${Price} * 0.10")
                        .addOutcome("Currency", "lookup(0, currencyLookup, toUpperCase(${Currency Code}))")
                        )
                ;
        
        DecisionTableResult result = table.evaluate(input);
        Record outcome = result.getOutcome();

        System.out.println("outcome = " + outcome);
    }

}

Code Walkthrough

1. A DefaultExpressionContext is defined as the input of the decision tree where we set properties such as Price, Currency Code.
2. BasicLookup is created to specify additional information about Currency. A new field Currency Name is added with five rows.
3. Then, a DecisionTable is initialized and currencyLookup specified in the previous step is applied.
4. Rules are defined in DecisionTableRule objects.
5. In order to add a condition to a rule, addCondition() method is called. As in the example, more than one condition can be applied to a single rule. 
6. addOutcome() method is invoked to attach an outcome with a rule.
7. The input is then evaluated and stored in a DecisionTableResult instance.
8. Finally, getOutcome() is invoked to display the results of the evaluation on the console.

Console Output

outcome = Record (MODIFIED) {
    0:[Shipping]:DOUBLE=[15.9]:Double
    1:[Currency]:STRING=[Canadian Dollars]:String
}