The methods in the Selector classes encapsulate common SOQL queries made by the application, such as selectById, as well as more business-related methods, such as selectByTeam. This helps the developers who consume the Selector classes identify the correct methods to use for the business requirement and avoids replication of SOQL queries throughout the application.
Each method also has some standard characteristics, such as the SObject fields selected by the queries executed, regardless of the method called. The overall aim is to allow the caller to focus on the record data returned and not how it was read from the database.
By now, you're starting to get the idea about naming conventions. The Selector classes and methods borrow guidelines from other layers with a few tweaks. Consider the following naming conventions when writing the Selector code:
Class names: in naming a Selector class, it typically follows the same convention as a Domain...
