To ensure that the Food_Preference__c picklist field has a value every time a record is created or updated, marking the field as Required on the field definition is the optimal solution.
Option C: Mark the field as Required on the field definition
Universal Enforcement: Setting the field as required at the field level ensures that it must have a value regardless of how the record is created or updated (UI, API, data import).
Data Integrity: Prevents records from being saved without a value in the picklist field, maintaining data consistency.
No Additional Code: Achieves the requirement declaratively without the need for Apex code.
Reference:
Making a Custom Field Required
Why Other Options are Less Optimal or Incorrect:
Option A: Mark the field as Required on the object's page layout
UI Only: This setting only enforces the requirement when users interact with the record via the specific page layout.
Not Universal: Does not prevent records from being saved without a value through the API, data import, or other page layouts.
Option B: Set "Use the first value in the list as the default value" to True Default Value: Automatically populates the field on new records but does not prevent users from clearing the value.
No Enforcement on Updates: Does not enforce a value on record updates if the field is cleared.
Option D: Write an Apex trigger to ensure a value is selected
Unnecessary Complexity: Writing code for a requirement that can be met declaratively adds unnecessary complexity.
Maintenance Overhead: Triggers require testing and ongoing maintenance.
Best Practices: Prefer declarative solutions over programmatic ones when possible.
Conclusion:
Marking the Food_Preference__c field as Required on the field definition ensures that a value is always selected when a record is saved, across all contexts.
It is the most efficient and maintainable solution.