How to handle Lists with different types

Question

I have a function that takes an object as a JSON body and returns a returns the list as a JSON body.

Here is the function:

public List<Event> executeRule(Rule rule) {
        List<Transaction> userTransaction = transactionsService.latestTransactionsForUser(rule.getUserId());
        List<Rule> ruleList = activeRulesForUser(rule.getUserId());

       return eventList;
}

From the object passed as a parameter I get userId and find all transactions and rules for a particular user. Now I have to return those transactions and rules of single user as new list of type Event .

What would be the best practice for it as I have two list with different types and third list that I have to return with also different type?

Answer 1

I supposed you want to return the user transactions and rules, if you are encountering these together many times, maybe it's a sign that you should wrap them in a class, as follows:

class UserEvents {

    private List<Transaction> transactions;
    private List<Rule> rules;
    
    public UserEvents(List<Transaction> transactions, List<Rule> rules) {
        this.transactions = transactions;
        this.rules = rules;
    }

    public UserEvents() {
        this(new ArrayList<>(), new ArrayList<>());
    }

    public List<Transaction> getTransactions() {
        return transactions;
    }

    public void setTransactions(List<Transaction> transactions) {
        this.transactions = transactions;
    }

    public List<Rule> getRules() {
        return rules;
    }

    public void setRules(List<Rule> rules) {
        this.rules = rules;
    }
}

Then your function will look something like this:

public UserEvents executeRule(Rule rule) {
    List<Transaction> transactions = transactionsService.latestTransactionsForUser(rule.getUserId());
    List<Rule> rules = activeRulesForUser(rule.getUserId());
    
    return new UserEvents(transactions, rules);
}

I would like to let you know that a function with 'execute' in it's name does not really need to return something, it should execute a task or something similar.

You should give descriptive and correct names to your functions and methods, one should understand only from the method decleration what the method does.

Answer 2

I found a working solution.

public List<Event> executeRule(Rule rule) {
        List<Transaction> userTransaction = transactionsService.latestTransactionsForUser(rule.getUserId());
        List<Rule> ruleList = activeRulesForUser(rule.getUserId());
        
        List<Event> eEventList = new ArrayList<>();
        Event event = new Event();
        event.setUserId(rule.getUserId());
        savingsEvent.setTransactions(userTransaction);
        savingsEvent.setSavingsRules(savingsRuleList);

        savingsEventList.add(savingsEvent);

       return savingsEventList;
    }

So the solution was to create a new object Event and populate it with data that I need from the two lists, then add that object to Event list.

In Event object I added both lists:

class Event {

    private Long id;
    private Long userId;
    private List<Transaction> transactions;
    private List<Rule> rules;
    
    //Getters, Setters, Constructors
}