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I have created a Synchronizer, the purpose of which is to read data from an XML source file and store the result in a DB.

I have different source types, for example Student.XML, School.XML, etc. These files are copied in my source directory, C:Source.

My Synchronizer watches the Source folder, and every time there is a new file, it should read it, map it to my domain class and write the domain class into the DB.

If C:Source folder contains Student.XML, it should read the content of the XML file and copy it in Student Table in the DB. If C:Source contains School.XML, it should read the file and copy the content to School Table.

To solve this, I have defined an ISyncer interface:

public interface ISyncer

 // Read input and synchronize destination, return error message if any
 string Sync();

Now all my Syncer types (e.g. StudentSyncer, SchoolSyncer, etc) should implement this interface:

public class StudentSyncer : ISyncer

 // simple XML reader, reads XML file into a list of List<XMLStudent>
 private XMLStudentReader _reader;

 public StudentSyncer(string file)
 
 _reader = new XMLStudentReader(file);
 

 public string Sync()
 
 // read the input
 List<XMLStudent> source = _reader.ReadAll();

 // using automapper map to domain object
 List<Student> dbStudent = Mapper.Map<List<XMLStudent>, List<Student>>(source);
 dbStudent.ForEach(s => s.IsCurrent = true); // set IsCurrent

 // write records to Student table, using Unit of Work patterns
 using (var context = new DbContext())
 
 UnitOfWork uow = new UnitOfWork(context);

 // set the existing records to not current
 var curSet = uow.Student.FindByTrackingChanges(s => s.IsCurrent == true).ToList();
 curSet.ForEach(s => s.IsCurrent = false);
 uow.Student.AddRange(dbStudent);
 uow.SaveChanges();
 

 return ""; // no error
 

I have a Windows service, which calls the DoSync() method every 30 seconds:

public void DoSync()

 foreach (string file in Directory.EnumerateFiles(@"C:Source", "*.xml"))
 
 // use syncer factory to initialize the correct instance of syncer based on input file name
 ISyncer syncer = _syncerFactory.CreateInstance(file);

 // do the synchronization task
 syncer.Sync();

 // Move file to processed folder
 MoveFile(@"C:Destination");
 

The Factory is a simple factory. It reads the source file name, e.g. Student.XML, School.XML and based on the file name. It initializes the correct Syncer, e.g. StudentSyncer, SchoolSyncer.

I am happy with the code, but it is bothering me because I feel it is not following the Single Responsibility Principle. My Syncer class is not doing 1 task, but it is doing 3 tasks: read input, map to domain class, write to DB.

How about extracting tasks common to all source types into an (abstract) base class that, in turn, implements your ISyncer interface?

I would also change the error reporting by using exceptions, rather than have the method return a string in case of error.

Edit, code example (C#-ish pseudo code)

abstract class SyncerBase : ISyncer

 sealed List<T> Map(List source, List target)
 
 // Mapping magic here
 

 sealed SaveToDB(List dataToSave, params ...)
 
 // Your database access here
 

Put utility methods and common stuff for all your synchronizers in that base class, and inherit it.

class StundentSyncer : SyncerBase

 // Constructor as in your code
 void Sync(string file)
 
 var XMLstudents = _reader.ReadAll();
 var students = Map(XMLstudents); // calling base class here!
 // Manipulate student list here as needed
 SaveToDB (students, database params here) // base class here, too