Abstract Method for a Base Class

Question

I've got a base class called DAL_Base for a large project that does most of the SQL lifting.

DAL_Base has fields for SELECT statements, a GetRecords() method, and a virtual FillData(IDataRecord) .

public class DAL_Base<T> where T : IDisposable, new() {

  private string connStr;

  public DAL_Base() {
    connStr = ConfigurationManager.ConnectionStrings["CompanyDatabaseConnStr"].ConnectionString;
  }

  internal string SP_GET { get; set; }

  internal SqlConnection m_openConn {
    get {
      var obj = new SqlConnection(connStr);
      obj.Open();
      return obj;
    }
  }

  internal virtual T FillDataRecord(IDataRecord record) {
    return new T();
  }

  internal TList<T> Get() {
    if (String.IsNullOrEmpty(SP_GET)) {
      throw new NotSupportedException(string.Format("Get Procedure does not exist for {0}.", typeof(T)));
    }
    var list = new TList<T>();
    using (var cmd = new SqlCommand(SP_GET, m_openConn)) {
      cmd.CommandType = cmd.GetCommandTextType();
      using (var r = cmd.ExecuteReader()) {
        while (r.Read()) {
          list.Add(FillDataRecord(r));
        }
      }
      cmd.Connection.Close();
    }
    return list;
  }

}

There is a lot more, but this should suffice for a single example.

TList is just a List<T> class:

internal class TList<T> : List<T> {
  public TList() { }
}

When one of my classes inherits from it, I wanted it to be able to override the base class's FillDataRecord(IDataRecord) .

For example, EmployeeDB ** inherits **DAL_BASE .

When I call EmployeeDB.GetEmployeeList() , it uses DAL_BASE to pull the records:

public class EmployeeDB : DAL_Base<Employee> {

  private static EmployeeDB one;

  static EmployeeDB() {
    one = new EmployeeDB() {
      SP_GET = "getEmployeeList",
    };
  }

  private EmployeeDB() { }

  internal override Employee FillDataRecord(IDataRecord record) {
    var item = base.FillDataRecord(record);
    item.Emp_Login = record.Str("Emp_Login");
    item.Emp_Name = record.Str("Emp_Name");
    item.Emp_Email = record.Str("Emp_Email");
    item.Emp_Phone = record.Str("Emp_Phone");
    item.Emp_Role = record.Str("Emp_Role");
    return item;
  }

  public static EmployeeList GetEmployeeList() {
    var list = new EmployeeList();
    list.AddRange(one.Get());
    return list;
  }

}

In the code above, when GetEmployeeList() calls the DAL_Base method Get() , only DAL_Base::FillDataRecord(IDataRecord) is called.

I really need EmployeeDB::FillDataRecord(IDataRecord) to be called, but I can't make DAL_Base::FillDataRecord(IDataRecord) abstract.

What is the way around this?

All I know of right now is to create an EventHandler , which is what I just thought of, so I'm going to work towards that.

If anyone knows of a better route, please chime in!

Answer 1

One solution is to pass a delegate for Derived.FillDataRecord to the base class via the constructor.

public class DAL_Base<T> where T : IDisposable, new() {

  private string connStr;

  public DAL_Base() {
    connStr = ConfigurationManager.ConnectionStrings["CompanyDatabaseConnStr"].ConnectionString;
  }
    private Func<IDataRecord, T> _fillFunc;

    public DAL_Base(Func<IDataRecord, T> fillFunc) : this() {
            _fillFunc = fillFunc;
    }

        // ... 
    internal TList<T> Get() {
    if (String.IsNullOrEmpty(SP_GET)) {
      throw new NotSupportedException(string.Format("Get Procedure does not exist for {0}.", typeof(T)));
    }
    var list = new TList<T>();
    using (var cmd = new SqlCommand(SP_GET, m_openConn)) {
      cmd.CommandType = cmd.GetCommandTextType();
      using (var r = cmd.ExecuteReader()) {
        while (r.Read()) {
          list.Add(_fullFunc(r));
}

and in the derived class:

public class EmployeeDB : DAL_Base<Employee> {
    public EmployeeDB() : base(r => FillDataRecord(r)) { }

  private Employee FillDataRecord(IDataRecord record) {
    var item = base.FillDataRecord(record);
    item.Emp_Login = record.Str("Emp_Login");
    item.Emp_Name = record.Str("Emp_Name");
    item.Emp_Email = record.Str("Emp_Email");
    item.Emp_Phone = record.Str("Emp_Phone");
    item.Emp_Role = record.Str("Emp_Role");
    return item;
  }
}