Build Configurable Business Rules (Custom Metadata)

List<Case_Routing_Rule__mdt> rules = [
    SELECT Priority__c, Case_Type__c, Queue_Name__c
    FROM Case_Routing_Rule__mdt
];

1. List<Case_Routing_Rule__mdt> rules = [ — custom metadata is queried with regular SOQL (Module 29).
2. SELECT Priority__c, Case_Type__c, Queue_Name__c — the fields needed.
3. FROM Case_Routing_Rule__mdt — the object.
4. ]; — closes the query — critically, this runs once per transaction, at the top of the handler method, following the same "collect, then act" instinct from Module 25.

Map<String, String> queueByPriorityAndType = new Map<String, String>();

for (Case_Routing_Rule__mdt rule : rules) {
    String key = rule.Priority__c + '|' + rule.Case_Type__c;
    queueByPriorityAndType.put(key, rule.Queue_Name__c);
}

1. Map<String, String> queueByPriorityAndType = new Map<String, String>(); — the lookup, keyed by a composite string.
2. (blank line)
3. for (Case_Routing_Rule__mdt rule : rules) { — loops over the rules, in memory.
4. String key = rule.Priority__c + '|' + rule.Case_Type__c; — combining Priority__c and Case_Type__c into a single composite key (Module 16's Map lesson, applied with a small trick: concatenating two values into one key).
5. queueByPriorityAndType.put(key, rule.Queue_Name__c); — stores the queue under that key.
6. } — closes the loop.

This lets every subsequent lookup be a single, instant Map.get() instead of looping through the rules list again for every Case.

public void beforeInsert(List<Case> newCases) {
    // ... field-access check from the previous lesson ...

    Map<String, String> queueByPriorityAndType = buildRoutingLookup();

    for (Case c : newCases) {
        String key = c.Priority + '|' + c.Type;
        if (queueByPriorityAndType.containsKey(key)) {
            c.Assigned_Queue__c = queueByPriorityAndType.get(key);
        }
    }
}

private Map<String, String> buildRoutingLookup() {
    List<Case_Routing_Rule__mdt> rules = [SELECT Priority__c, Case_Type__c, Queue_Name__c FROM Case_Routing_Rule__mdt];
    Map<String, String> lookup = new Map<String, String>();
    for (Case_Routing_Rule__mdt rule : rules) {
        lookup.put(rule.Priority__c + '|' + rule.Case_Type__c, rule.Queue_Name__c);
    }
    return lookup;
}

1. public void beforeInsert(List<Case> newCases) { — the entry point.
2. // ... field-access check from the previous lesson ... — unchanged from before.
3. (blank line)
4. Map<String, String> queueByPriorityAndType = buildRoutingLookup(); — the lookup is built once.
5. (blank line)
6. for (Case c : newCases) { — loops over the new Cases.
7. String key = c.Priority + '|' + c.Type; — builds the same kind of composite key.
8. if (queueByPriorityAndType.containsKey(key)) { — checks the lookup.
9. c.Assigned_Queue__c = queueByPriorityAndType.get(key); — assigns the matching queue, one Map.get() each, entirely in memory.
10. } — closes the if.
11. } — closes the loop.
12. } — closes the method.
13. (blank line)
14. private Map<String, String> buildRoutingLookup() { — the helper.
15. List<Case_Routing_Rule__mdt> rules = [SELECT Priority__c, Case_Type__c, Queue_Name__c FROM Case_Routing_Rule__mdt]; — the one query.
16. Map<String, String> lookup = new Map<String, String>(); — the lookup being built.
17. for (Case_Routing_Rule__mdt rule : rules) { — loops over the rules.
18. lookup.put(rule.Priority__c + '|' + rule.Case_Type__c, rule.Queue_Name__c); — stores each one.
19. } — closes the loop.
20. return lookup; — hands back the completed lookup.
21. } — closes the helper.

However many Cases there are in newCases, this is exactly Module 25's bulkification discipline, now applied to configuration data instead of database records.