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
];

Custom metadata is queried with regular SOQL (Module 29), but critically, this runs once per transaction, at the top of the handler method — not once per Case, 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);
}

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) 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;
}

The lookup is built once, and every Case in newCases — however many there are — does one Map.get() each, entirely in memory. This is exactly Module 25's bulkification discipline, now applied to configuration data instead of database records.