Custom Fields
By the end of this lesson, you'll be able to:
- Add a custom field to either a standard or custom object conceptually
- Recognize common custom field data types
- Explain why a custom field also carries the __c suffix
Prerequisites: "Custom Objects"
Custom fields on a standard object
Account acc = new Account();
acc.Name = 'Acme Logistics';
acc.Fleet_Size__c = 45; // a custom field added to the standard Account objectAccount ships with fields like Name and Industry built in, but a logistics company might need to track Fleet_Size__c — a custom field an admin added specifically for their business, living right alongside the standard fields on the same object.
Common custom field data types
acc.Fleet_Size__c = 45; // Number
acc.Annual_Contract_Value__c = 250000.00; // Currency
acc.Is_Preferred_Vendor__c = true; // Checkbox (Boolean)
acc.Contract_Start_Date__c = Date.today(); // Date
acc.Account_Tier__c = 'Platinum'; // Picklist (stored as String in Apex)Custom fields map onto familiar Apex types — Integer/Decimal for Number/Currency, Boolean for Checkbox, Date for Date fields, and String for both Text and Picklist fields. In Apex, a Picklist value is just a String — Apex itself doesn't enforce which specific values are valid, that validation happens at the platform level.
Why __c applies to fields too
Just like custom objects, every custom field's API name ends in __c — Fleet_Size__c, not FleetSize. This means you can tell at a glance, reading Apex code, exactly which fields were built into the object by Salesforce (no suffix, like Name) and which were added specifically for this org (__c).
Exercise
Add three custom field assignments to this Account: a Number field Employee_Count__c, a Checkbox Is_Active_Customer__c, and a Date Onboarded_Date__c.
Show hint
Match each Salesforce field type to an Apex type: Integer, Boolean, Date.
Custom Fields Quiz
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Summary
A custom field extends an existing object — standard or custom — with additional business-specific data, following the same __c naming convention as custom objects.