Declarative versus Programmatic Customization

What it is

Salesforce can be customized with declarative tools (clicks: fields, formulas, validation rules, Flow, page layouts) or programmatic tools (code: Apex, SOQL, Lightning Web Components, Visualforce).

The platform's guidance is clear: use declarative tools when they meet the requirement, because they are faster to build, easier to maintain and upgrade safely. Use code when the requirement is beyond what clicks can do.

How it works

Choosing the tool

Formula fields

• Read-only fields calculated each time the record is read; nothing is stored.
• Can reference fields on parent records through relationships (cross-object formulas), such as Account.Industry on Contact.
• Cannot reference child records; use a roll-up summary or code for that.
• Limits apply: a formula can hold up to 3,900 characters, and its compiled size is limited to 5,000 bytes.

A developer trap: after insert in Apex, a formula field on the in-memory record is not recalculated. Query the record again, or call Formula.recalculateFormulas(), to get the value.

Opportunity o = new Opportunity(Name = 'Q4', StageName = 'Prospecting',
    CloseDate = Date.today(), Amount = 100);
insert o;
System.debug(o.Margin__c);   // null: formula not recalculated in memory
o = [SELECT Margin__c FROM Opportunity WHERE Id = :o.Id];

Roll-up summary fields

• Defined on the master of a master-detail relationship.
• Functions: COUNT, SUM, MIN and MAX, with optional filter criteria on the child records.
• Recalculated automatically when detail records change, as part of the save order of execution.
• Not available on lookup relationships. For those, use a record-triggered flow or an Apex trigger that aggregates the children.

How governor limits shape the decision

Declarative automation is not free: record-triggered flows and Apex triggers run in the same transaction and share the same governor limits. A flow's Get Records element counts toward the 100 SOQL query limit, just like a query in a trigger.

A worked example

A company wants each Account to show the number of open Cases, and Case has a lookup to Account. A roll-up summary field is not possible, because roll-ups need master-detail and Case cannot be the detail of Account.

The options are a record-triggered flow on Case that recounts open cases for the parent, or an Apex trigger on Case that collects Account Ids in a Set<Id>, runs one aggregate query and updates the accounts in one DML statement. If the rest of the logic is simple, the flow is the declarative first choice; if the org already has a Case trigger framework or the volume is large, the trigger fits.

How the exam asks about this

• "Show the parent's field on the child record." A cross-object formula field.
• "Sum the amounts of detail records on the master." A roll-up summary field.
• "Count child records related by a lookup." Flow or an Apex trigger; roll-up summaries need master-detail.