The key principle of the Domain layer pattern is to lay out the code in such a way that it maps to the business domain of the application. In a Lightning application, this is typically supported by Custom Objects. As such, it's important to clearly indicate which Domain layer class relates to which Standard or Custom Object:

• Avoid acronyms: As per the previous chapter, try to avoid these unless it makes your class names unworkably long.
• Class names: Use the plural name of your Custom Object for the name of your Domain class. This sets the tone for the scope of the record that the class deals with as clearly being bulkified, as described in the following subsection:
  • Some bad examples are Race.cls and RaceDomain.cls.
  • Some good examples are Races.cls and Teams.cls.
• Method names: Methods that relate to the logic associated with database operations or events should follow the onEventName convention. Other method names should be descriptive and avoid repeating the name of the class as part of the name:
  • Some bad examples are Races.checkInserts and Races.startRace.
  • Some good examples are Races.onBeforeInsert and Races.start.
• Parameter names and types: Much of what was described in the previous chapter applies here. Though passing in a list of records to the Domain class methods is not required, this is available as a class member variable to all the Domain class methods, as you will see later in this chapter:
  • Some bad examples are as follows:

Races.onBeforeInsert( 
  List<Race__c>racesBeingInserted) 
Races.start( 
  List<Id>raceIds) 

• • Some good examples are as follows:

Races.onBeforeInsert() 
Races.start()

• Inner classes and interfaces: Much of what was described in the previous chapter also applies here. As the data being managed is expressed in terms of the actual Custom Objects themselves and that information is available as a class member variable, there is typically less of a need for inner classes representing data to be passed in and out of a Domain class.

The following diagram shows how the Domain classes that are used in this chapter map to their respective Custom Objects:

Each Domain class receives the records that its methods act on in its constructor. The methods shown in the Domain classes are described in more detail as we progress through this chapter.