Custom Metadata Types

Custom settings and regular records both live purely in an org's data — they don't automatically move when code is deployed from a sandbox to production. Custom metadata records are different: they're treated as metadata, the same category as an Apex class or a custom field, meaning they deploy right alongside code changes.

List<Discount_Rule__mdt> rules = [
    SELECT Label, Discount_Percent__c, Minimum_Order_Amount__c
    FROM Discount_Rule__mdt
];

for (Discount_Rule__mdt rule : rules) {
    System.debug(rule.Label + ': ' + rule.Discount_Percent__c + '%');
}

Custom metadata's API name ends in __mdt (rather than __c), and — unlike list custom settings — it's queried with regular SOQL syntax, just like any object from Module 20. It doesn't hit the cached-read path custom settings use, but it gains something custom settings can't offer: deployability.

Imagine a set of discount rules that must be identical across a sandbox and production, tested together with the Apex logic that reads them. Custom metadata records travel in the same deployment as that Apex code — a change set or package includes both together, staying in sync. A custom setting's values, by contrast, would need to be manually re-entered (or migrated with a separate data tool) in every environment.