3 Tier Development Data Retrieval Help

Member 11228069 wrote:

3 tier app: UI,CAR OBJECT,DATA ACCESS

Those are layers, not tiers -- layers are awesome.

Don't try to write one method that will perform all the data access; write a method for each operation that needs to be performed -- and use parameters to provide values to the statements.

Performance can be improved by reusing objects rather than throwing them out and recreating them. This, of course, assumes a system that does a lot of operations. It may not matter much in your current situation, but you could run into a situation in the future where it does matter, and developing good habits now will pay of later.

I recommend you not use DataAdapters, but if you do, remember that the adapter will open and close the Connection for you, so you needn't do that.

That catch is a very bad idea; not only does it not provide any benefit, it actually makes things worse. Either...
0) Simply remove the try/catch
1) Add some information to the Data property of the Exception -- e.Data [ "CommandText" ] = selectStr ;
and rethrow ; -- throw ;
2) If you want to throw a more informative Exception, then include the original Exception as the InnerException -- throw new UnableToFetchDataException(e.Message,e);
3) Both 1 and 2 (recommended)

Ok thanks for your help, here is my add method in the data access layer, does this look ok?

public void Add(carObject carObj)
      {
          try
          {
              string addString = @"INSERT INTO cars (MAKE,MODEL,COLOUR,YEAR,MILEAGE,CONDITION) VALUES (@Make,@Model,@Colour,@Year,@Mileage,@Condition)";

              OpenConnection();


              SqlCommand cmd = new SqlCommand(addString, Conn);

              cmd.Parameters.AddWithValue("@Make", carObj.Make);
              cmd.Parameters.AddWithValue("@Model", carObj.Model);
              cmd.Parameters.AddWithValue("@Colour", carObj.Colour);
              cmd.Parameters.AddWithValue("@Year", carObj.Make);
              cmd.Parameters.AddWithValue("@Mileage", carObj.Mileage);
              cmd.Parameters.AddWithValue("@Condition", carObj.Condition);


              cmd.ExecuteNonQuery();
              cmd.Dispose();
              CloseConnection();
          }
          catch (Exception e)
          {
              throw new Exception(e.Message, e);
          }
      }

and I call this function from the business layer (carobject)

public void addCarToDb()
     {
         carData.Add(this);

     }