Implementing the custom query logic

If we take a look at the implementation of the fflib_SObjectSelector.selectSObjectById base class method (at the time of writing this book), it is quite simple and gives a template as to the way we can implement custom Selector methods; it also highlights other base class methods we can use:

public List<SObject> selectSObjectsById(Set<Id> idSet)
{
  assertIsAccessible();
  return Database.query(buildQuerySObjectById());
}
private String buildQuerySObjectById()
{ 
  return String.format(
    'SELECT {0} FROM {1} WHERE id in :idSet ORDER BY {2}', 
     new List<String> 
       {getFieldListString(),getSObjectName(),getOrderBy()}); 
}

The getFieldListString method calls the getSObjectFieldList and getSObjectFieldSetList methods implemented in the preceding code. It basically takes the SObjectField lists that result from these methods and builds a single comma-delimited list of fields ready to be inserted into the SOQL query string. Also, note...